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#LIBR'KfiY
Michigan State
University

 

 

 

This is to certify that the

dissertation entitled

Effect of Temperature on the
Behavior of Biradical Intermediates:

Conformational Control of Product Ratios

in Photocyclization React1ons
presented by

Ali Reza land

has been accepted towards fulfillment
of the requirements for

Ph.D. degreein Chemistry

9%

a rprofe“r
D te fl/o'y. “3/779

 

MS U i: an Affirmative Action/Equal Opportunity Institution 0-12771

PLACE ll RETURN BOX to remove thle checkout from your record.
TO AVOID FINES return on or before dete due.

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU le An Atflnnetlve AotlorVEquel Opportunity lnetltttton
mama-m

Effect of Temperature on the Behavior of Biradical Intermediates:

Conformational Control of Product Ratios in Photocyclization Reactions

by

Ali Reza Zand

A DISSERTATION

Submitted to
Michigan State University
In partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Chemistry

1996

Abstract

Effect of Temperature on the Behavior of Biradical Intermediates:
Conformational Control of Product Ratios in Photocyclization

Reactions
by

Ali Reza Zand

The photochemistry of several ketones at various temperatures was investigated.
Intramolecular 6-hydrogen abstraction by excited carbonyl groups results in formation of
1,5-biradicals which upon cyclization yield indanols as photoproducts. This investigation
probed the effect of temperature on the diastereoselectivity of cyclization with emphasis
on the role of intersystem crossing on product ratios.

a—Arylacetophenones show variable product ratios at various temperatures. The
Arrhenius plots are linear indicative of conformational equilibrium. The results show
nonenthalpic factors to be as important as enthalpic differences at determining
diastereoselectivity. The low diastereoselectivities observed for a—(2-benzylphenyl)-
acetophenones is attributed to benzylic conjugation which imparts rotational freedom to
both ends of the biradical intermediate. a-Aryl propiophenones show a large preference
for the a-methyl group and the phenyl to be trans in the 2-phenyl-2-indanol product. This
phenomenon seems to stem from the lowest energy “reactive ground state conformer” of

the ketones which always mirrors one of the biradical minima.

Irradiation of a-arylacetones results in formation of indanols and a-cleavage
products. Indanol formation involves a singlet state 5-hydrogen abstraction followed by
Yang cyclization while a-cleavage occurs from the triplet state. The fact that a-cleavage
is the predominant photoreaction at low temperatures has been attributed to a competition
between hydrogen abstraction which has a barrier and a barrierless intersystem crossing
process. a-Arylacetones show lower indanol diastereoselectivities than their
acetophenone analogs. This has been attributed to conformational control, rather than
ground state control, of diastereoselectivity. The low product quantum yields of or-
arylacetones have been attributed to a well known radiationless decay process which
competes with singlet state hydrogen abstraction.

o-tert—Butyl-a,a,a-trifluroacetophenone, like 0-tert-butylacetophenone, forms an
indanol and an unsaturated alcohol upon irradiation in benzene and methanol. The
unsaturated alcohol is the major product under all conditions. Capto-dative resonance
thus does not provide sufficient stabilization to allow the hydroxy end of the biradical to
twist out of benzylic conjugation to give higher indanol yields.

2-(2’-(2’,3’-Dimethyl)butyl)benzophenone forms three iSOmeric indanols and an
unsaturated alcohol upon irradiation in solution and in the solid state. Two different
reaction sites, isopropyl and methyl, seem to have comparable reactivity which shows the
insensitivity of hydrogen abstraction rates to orientational factors. Formation of the
unsaturated alcohol mimics the o-tert-butylacetophenone derivatives and could explain

the less than unity quantum yields previously observed for tert-amylbenzophenones.

This Thesis is Ded'
icated To My Grandmothers Who Passed away Bef I G
ore raduated

iv

Acknowledgments

The Author wishes to thank Dr. Peter J. Wagner for his help, guidance, sense of
humor and innumerable entertaining discussions during the course of this work.

The author is grateful to the National Science Foundation and Michigan State
University for financial support in the form of teaching, research assistantships and the
Hart fellowship. The author would also like to thank the Chemistry Department for the
use of its excellent facilities.

The author also owes special thanks to fi-iends in the Wagner research group.
Their help and support made my graduate career much more enjoyable. Last, but by no
means least, I would like to thank my family for their help, support and patience

throughout my graduate career.

Table of Contents

 

 

 

 

 

 

 

 

 

 

TABLE OF CONTENTS vi
LIST OF FIGURES viii
LIST OF TABLES x
LIST OF SCHEMES xii
LIST OF ABBREVIATIONS xiv
INTRODUCTION 1
I. MEASUREMENTS OF QUANTUM YlELDS AND EXCITED STATE LIFETIMES .................................................... 3
II. A-CLEAVAGE REACTIONS ............................................................................................................................ 5
III. HYDROGEN ABSTRACTION .............................................................................................. 8
A. Conformational Control of Photoreactivity ........................................................................................ II
B. Orientational Requirements of Hydrogen Abstraction ......................................................................... l 4
C. 6-Hydrogen Abstraction ....................................................................................................................... 21
D. Nature of the Excited State- Singlet vs. Triplet .................................................................................... 25
E. Eflect of Environment ........................................................................................................................... 28
F. Biradical Lifetime ................................................................................................................................. 30
G. Diastereoselectivity .............................................................................................................................. 34
H. Photoenolization of a—(2, 4, 6-tritsopropylphenyl)acetophenone ......................................................... 36
IV. GOALS OF RESEARCH ............................................................................................................................... 38
RESULTS 40
I. A-ARYLACETOPHENONES AND DERIVATIVES .............................................................................................. 40
A. General Preparation of the Ketones .................................................................................................... 40
B. Irradiation of Ketones .......................................................................................................................... 4]
C. Steady-State Photokinetics. .................................................................................................................. 60
II. A-ARYLACETONES ..................................................................................................................................... 62
A. General Preparation of the Ketones. ................................................................................................... 62
B. Irradiation of Ketones .......................................................................................................................... 62
C. Identification of Photoproducts ........................................................................................................... 63
D. Steady-State Photokinetics ................................................................................................................... 70
III. 2-TERT-BUTYL TRIFLOROACETOPHENONE ............................................................................................... 72
A. Preparation .......................................................................................................................................... 72
B. Irradiation Conditions .......................................................................................................................... 72
C. Identification of Photoproducts ........................................................................................................... 72
IV. 2'-(2,3-DlMETHYL-2-BUTYL)BENZOPHENONE .......................................................................................... 74
A. General Preparation ............................................................................................................................ 74
B. Irradiation Conditions .......................................................................................................................... 74
C. Identification of photoproducts. ........................................................................................................... 75
D. Steady-State Photokinectics ................................................................................................................. 78
V. SEMIEMPIRICAL CALCULATIONS ............................................................................................................... 79
DISCUSSION 90
I. CONFORMATIONAL CONTROL OF PRODUCT RATIOS FROM TRIPLET 1,5-BIRADICALS ................................ 90
II. PHOTOBEHAVIOR 0F A-ARYLACETONES- A COMPARISON OF SINGLET AND TRIPLET BIRADICAL
BEHAVIOR ........................................................................................................................ l 10
III. PHOTOENOLIZATIONS OF A-(2, 4 ,6-TRIISOPROPYLPl-IENYL)ACETOPHENONE AND ACETONE ................... l 15

vi

IV. PHOTOBEHAVIOR or O-TERT-BUTYLTRIFLUOROACETOPHENONE ......................................................... l 18
V. PHOTOBEHAVIOR or 2-(2’-(2’,3’-D1METHYLBUTYL))BENZOPHEN0NE - EFFECT or DIHEDRAL ANGLE ON

 

HYDROGEN ABSTRACTION RATES ............................................................................................................... 120
EXPERIMENTAL 131
I. GENERAL PROCEDURES ............................................................................................................................ l3l
II. PREPARATION OF STARTING KETONES .................................................................................................... I32
a-(Z-Ethylphenyl) -fl,,6,fl-trideuteropropiophenone (4 d3) ...................................................................... I 32
a—(Z-Ethylphenyvpropiophenone (4) ..................................................................................................... I37
a-(2-Ethylphenyl)acetone (I 0) ............................................................................................................... I38
a-Mesitylacetone ( l I )....; ....................................................................................................................... I40
a—(2—Benzylphenyl)propiophenone (7) .................................................................................................. l 42
a—(2, 4, 6- Triethylphenyl) -)3,fl,,6-tridueteropropiophenone (5 d 3) ........................................................... I45
a-(2, 4, 6-Triethylphenyl)propiophenone (5) .......................................................................................... I 50
a-(Z, 4, 6- Triethylphenyl)acetone (12) .................................................................................................... 150
a-(2, 4, 6- T ritsopropylphenyUacetone (I 3) ............................................................................................. I 52
a—(2, 4, 6- Trizsopropylphenyl)acetophenone (9) ..................................................................................... l 5 5
o-tert-Butyl-ma, a-trifluroacetophenone (l 4) ........................................................................................ 15 7
o-(2, 3-Dimethyl-2-buty1)bemophenone (15) .......................................................................................... I 60
III. PHOTOCHEMICAL EXPERIMENTS AND PROCEDURES ........................................................................ j ...... 166
A. Purification of Chemicals ................................................................................................................... I 66
B. Equipment and Procedures ................................................................................................................ l 6 7
C. Identification of Photoproducts ......................................................................................................... l 6 9
D. Quantitative Measurements ............................................................................................................... 219
REFERENCES: . 251

 

vii

List- of Figures

 

 

 

 

 

 

 

 

 

 

FIGURE 1. SIMPLIFIED JABLONSKI DIAGRAM .................................................................................................. 1
FIGURE 2.. ......................................................................................................... 15
FIGURE 3. ORIENTATIONAL REQUIREMENTS FOR H- ABSTRACTION ............................................................... 15
FIGURE 4. EFFECT OF DIHEDRAL ANGLE ON REACTIVITY .............................................................................. l7
HGURE 5. EFFECT OF DIHEDRAL ANGLE ON REACTIVITY .............................................................................. 18
FIGURE 6. CORRELATION DIAGRAM ............................................................. 27
FIGURE 7. MINIMUM ENERGY GEOMETRIES OF A- (2- ETHYLPHENYL)ACETOPHENONE .................................. 80
FIGURE 8. MINIMUM ENERGY GEOMETRIES OF A-(2 ,4 6-TRIETHYLPHENYL)ACETOPHENONE ....................... 80
FIGURE 9. LOWEST ENERGY CONFORMERS OF A-(2-ETHYLPHENYL)PROPIOPHENONE ................................... 81
FIGURE 10. LOWEST ENERGY GEOMETRIES OF A-(2,4,6-'IRIETHYLPHENYL)PROPIOPHENONE ....................... 82
FIGURE 1 1. MINIMUM GEOMETRIES OF A-(2-BEN2YLPHENYL)ACETOPHENONE ............................................ 83
FIGURE 12. LOWEST ENERGY CONFORMERS OF A-(2-BENZYLPHENYL)PROPIOPHENONE ............................... 83
FIGURE 13. LOWEST ENERGY GEOMETRIES OF A-MESITYLPROPIOPHENONE ................................................. 84
FIGURE 14. LOWEST ENERGY GEOMETRY OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETOPHENONE ................... 85
FIGURE 15. LOWEST ENERGY GEOMETRIES OF A-(2-E1HYLPHENYL)ACETONE ............................................. 85
FIGURE 16. LOWEST ENERGY CONFORMERS OF A-MESITYLACETONE ........................................................... 86
FIGURE 17. LOWEST ENERGY GEOMETRIES OF A-(2.4,6-TRIETHYLPHENYL)ACETONE .................................. 87
FIGURE 18. LOWEST ENERGY GEOMETRY OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETONE .............................. 87
FIGURE 19. LOWEST ENERGY GEOMETRY OF 2-TERT-BUTYLTRIFLOUROACETOPHENONE ............................. 88
FIGURE 20 ................................................................................................ 89
FIGURE 21. LOWEST ENERGY BIRADICAL CONFORMATIONS OF 2 ..... 96
FIGURE 22. LOWEST ENERGY GROUND STATE CONFORMATIONS OF 2 .......................................................... 97
FIGURE 23. LOWEST ENERGY BIRADICAL CONFORMATIONS OF 3 ......... ' ......................................................... 99
FIGURE 24. LOWEST ENERGY GROUND STATE CONFORMATIONS OF 8 ........................................................ 100
FIGURE 25. LOWEST ENERGY BIRADICAL CONFORMATIONS OF 8 ................................................................ 101
FIGURE 26. LOWEST ENERGY BIRADICAL CONFORMATIONS OF 5 ................................................................ 105
FIGURE 27. LOWEST ENERGY GROUND STATE CONFORMATIONS OF 5 ........................................................ 107
FIGURE 28. LOWEST ENERGY BIRADICAL CONFORMATIONS OF 4 ................................................................ 108
FIGURE 29. LOWEST ENERGY GROUND STATE CONFORMATIONS 0F 4 ........................................................ 109
FIGURE 30. LOWEST ENERGY BIRADICAL CONFORMATIONS OF 10 .............................................................. 1 14
FIGURE 31. LOWEST ENERGY GROUND STATE AND BIRADICAL CONFORMERS OF 9 AND 13 ....................... l 16
FIGURE 32 ................................. 121
FIGURE 33. VARIABLE TEMPERATURE NMR OF A-(2, 4, 6- -TRIETHYLPHENYL)-B, B, B- TRIDEUTERIO-
PROPIOPHENONE IN ACETONE- D6 ....................................................................................................... 149
FIGURE 34. lH NMR OF A-(2-ETHYLPHENYL)ACETOPHENONE BEFORE AND AFTER IRRADIATION IN
TOLUENE (A > 290 NM) ...................................................................................................................... 171
FIGURE 35. ‘H NMR SPECTRA OF A-(2,4,6-1RIETHYLPHENYL)ACETOPHENONE BEFORE AND AFTER
IRRADIATION IN TOLUENE (A>290 NM) .............................................................................................. 175
FIGURE 36. 'H NMR SPECTRA OF A-(z-ETHYLPHENYL)PROPIOPHENONE BEFORE AND AFTER IRRADIATION
IN TOLUENE (A>290 NM) .................................................................................................................... 182
FIGURE 37. 'H NMR SPECTRA OF A-(2,4,6-TRIETHYLPHENYL)PROPIOPHENONE BEFORE AND AFTER
IRRADIATION IN TOLUENE (A>290 NM) ......... - .......................................................... 186
FIGURE 38. 'H NMR SPECTRA OF A-(2-BENzYLPHENYL)ACETOPHENONE BEFORE AND AFTER IRRADIATION
IN TOLUENE (A>290 NM) .......................................................................................... 191
FIGURE 39. ‘H NMR SPECTRA OF A- MESITYLPROPIOPHENONE BEFORE AND AFTER IRRADIATION IN
TOLUENE (A>290 NM) ....................................................................................... 195
FIGURE 40. ‘H NMR OF A-(2, 4 6-1111lSOPROPYLPHENYL)ACETOPHENONE AFTER IRRADIATION IN TOLUENE
(A > 290NM) -- ................................................................................................. 197
FIGURE 41. 'H NMR OF THE lNDANOL MIXTURE FROM A-(2- -ETHYLPHENYL)ACETONE IN BENZENE .......... 203

viii

FIGURE 42. III NMR OF THE METHYL REGION OF THE INDANOL MIXTURE FROM A-(Z-ETHYLPHENYL)-

ACETONE IN BENZENE ........................................................................................................................ 207
FIGURE 43. 1H NMR OF THE METHYLENE REGION OF THE lNDANOL MIXTURE FROM A-(2-

ETHYLPHENYL)ACETONE IN BENZENE ................................................................................................ 208
FIGURE 44. 1H NMR OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETONE AFTER IRRADIATION IN TOLUENE (A >

290 NM, T= 297 K) ..................................................................................... 213

ix

List of Tables

 

 

 

 

 

TABLE 1. A-SUBST'ITUENT EFFECT ON o-TOLYLACETOPHENONE DERIVATIVES ............................................ 24
TABLE 2. DIASTEREOSELECTTVITY IN PHOTOCYCLOADDITION OF BENZALDEHYDE TO CYCLOALKENES ....... 35
TABLE 3. CHEMICAL YIELDS OF PHOTOPRODUCTS OF A-(2-ETHYLPHENYL)ACETOPHENONE IN TOLUENE AT
VARIOUS TEMPERATURES (A > 290) ..................................................................................................... 43
TABLE 4. CHEMICAL YIELDS OF PHOTOPRODUCTS OF A-(2,4,6-TRIETHYLPHENYL)ACETOPHENONE IN
TOLUENE AT VARIOUS TEMPERATURES (A >290) - ................................. ..45
TABLE 5. CHEMICAL YIELDS OF PHOTOPRODUCTS OF A-(o-TOLYL)PROPIOPHENONE IN TOLUENE AT VARIOUS
TEMPERATURES (A >290) ..................................................................................................................... 46
TABLE 6. CHEMICAL YIELDS OF PHOTOPRODUCTS OF A—(2-ETHYLPHENYL)PROFIOPHENONE IN TOLUENE AT
VARIOUS TEMPERATURES (A >290 NM) .......................................................................... 49
TABLE 7. CHEMICAL YIELDS OF PHOTOPRODUCTS OF A—(2, 4 ,6-TRIETHYLPHENYL) PROPIOPHENONE IN
TOLUENE AT VARIOUS TEMPERATURES (A > 290 NM) ......................................................................... 50
TABLE 8. CHEMICAL YIELDS OF PHOTOPRODUCTS OF A-(2- BENZYLPHENYL)ACETOPHENONE IN TOLUENE AT
VARIOUS TEMPERATURES (A > 290 NM) ................................................................ 53
TABLE 9. CHEMICAL YIELDS OF PHOTOPRODUCTS OF A-MESITYLPROPIOPHENONE IN TOLUENE AT VARIOUS
TEMPERATURES (A > 290 NM) .............................................................................................................. 55
TABLE 10. MOLAR ABSORPTTVIT'Y COEFFICIENTS (M‘CM") OF 9 AND ITS ENOL AT VARIOUS WAVELENGTHSS7
TABLE 1 1. PRODUCT QUANTUM YIELDS OF 9 As A FUNCTION OF CONVERSION AND WAVELENGTH ............. 58
TABLE 12. PRODUCT RATIOS OF IRRADIATION OF 9 UNDER VARIOUS CONDmONS ...................................... 59
TABLE 13. LIFETIMES OF TRIPLET ACETO- AND PROPIOPHENONES IN BENZENE ........................................... 60
TABLE 14. QUANTUM YIELDS OF PHOTOPRODUCTS FROM ACETO- AND PROPIOPHENONES IN BENZENE ...... 61
TABLE 15. CHEMICAL YIELDS OF PHOTOPRODUCTS FROM A-(2-ETHYLPHENYL)ACETONE IN TOLUENE AT
VARIOUS TEMPERATURES (A > 290 NM) .............................................................................................. 65
TABLE I6. CHEMICAL YIELDS OF PHOTOPRODUCTS FROM A-MESITYLACETONE IN TOLUENE AT VARIOUS
TEMPERATURES (A > 290 NM) .............................................................................................................. 67
TABLE 17. PRODUCT CHEMICAL YIELDS OF A-(2,4,6-T‘RIETHYLPHENYL)ACETONE IN TOLUENE AT VARIOUS
TEMPERATURES (A >290 NM) ............................................................................................................... 68
TABLE 18. PRODUCT CHEMICAL YIELDS OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETONE As A FUNCTION OF
CONVERSION AND TEMPERATURE ........................................................................................................ 70
TABLE 19. TRIPLET LIFETIMES OF A-ARYLACETONES IN BENZENE AT ROOM TEMPERATURE (A= 313
NM) ....................................................................................................................................................... 71
TABLE 20. QUANTUM YIELDS OF PHOTOPRODUCTS OF A-ARYLACETONES IN BENZENE AT ROOM
TEMPERATURE (A=313 NM) .................................................................................................................. 71
TABLE 21 . EFFECT OF TEMPERATURE AND MEDIUM ON PRODUCT RATIOS OF 15 .......................................... 77
TABLE 22. TRIPLET LIFETIMES AND PRODUCT QUANTUM YIELDS OF 2-(2'-(2',3'-DIMETHYL)BUTYL)-
BENZOPHENONE AT ROOM TEMPERATURE (A= 313 NM) ...................................................................... 78
TABLE 23. EFFECT OF TEMPERATURE ON THE lNDANOL RATIOS OF A-ARYLACETOPHENONES ..................... 91
TABLE 24. ARRHENIUS DATA FROM GRAPH 2 ............................................................................................... 92
TABLE 25. ARRHENIUS DATA FROM GRAPH 3 ............................................................................................. 103
TABLE 26. EFFECT OF TEMPERATURE ON PRODUCT RATIOS FROM A-ARYLACETONES ............................... l 1 1
TABLE 27 . EFFECT OF TEMPERATURE AND MEDIUM ON PRODUCT RATIOS OF 15 ........................................ 124
TABLE 28. DETAILS OF GLOBAL MINIMIZATIONS FOR COMPOUNDS 1-9 ...................................................... 221
TABLE 29. DETAILS OF GLOBAL MINIMIZATIONS FOR COMPOUNDS 10-15 .................................................. 222
TABLE 30. GRID OF ENERGIES FOR THE GROUND STATE OPTIMIZATION OF A-(2-ETHYLPHENYL)
ACETOPHENONE ........................................................................................................................ . ......... 223
TABLE 31. GRID OF ENERGIES FOR GLOBAL MINIMIZATION OF THE TRIPLET BIRADICAL OF A-(2,4,6-
TRIETHYLPHENYL)ACETOPHENONE .................................................................................................... 224
TABLE 32. GRID OF ENERGIES FOR GLOBAL MINIMIZATION OF THE TRIPLET BIRADICAL OF A-(2-
TOLYL)PROPIOPHENONE ..................................................................................................................... 225

 

 

 

 

 

TABLE 33. GRID OF ENERGIES FOR GLOBAL MINIMIZATION OF THE TRIPLET BIRADICAL OF A-(2-
ETHYLPHENYL)PROPIOPHENONE ................................................ 226
TABLE 34. GRID OF ENERGIES FOR GLOBAL MINIMIZATION OF THE TRIPLET BIRADICAL OF A-(2, 4, 6-
TR]ETHYLPHENYL)PROPIOPHENONE ................................................................... 227
TABLE 35. GRID OF ENERGIES FOR GLOBAL MINIMIZATION OF THE TRIPLET BIRADICAL OF A-
MESITYLPROPIOPHENONE ................................................................................................................... 228
TABLE 36.GRID OF ENERGIES FOR GLOBAL MINIMIZATION OF THE TRIPLET BIRADICAL OF A-(2-
ETHYLPHENYL)ACETONF .................................................................................. 229
TABLE 37. GRID OF ENERGIES FOR GLOBAL MlNlMlZATlON OF THE SINGLET BIRADICAL OF A-(2-
ETHYLPHENYL)ACETONE ................................................................................ 230
TABLE 38. GRID OF ENERGIES FOR GLOBAL MINIMIZATION OF THE TRIPLET BIRADICAL OF A- (2, 4, 6-
T‘RIISOPROPYLPHENYL)ACETONE ............................................................................. 23 1
TABLE 39. PRODUCT QUANTUM YIELDS OF A-(2-ETHYLPHENYL)ACETOPHENONE IN BENZENE .................. 234
TABLE 40. PRODUCT QUANTUM YIELDS OF A-(2,4,6-TRIETHYLPHENYL)ACETOPHENONE IN BENZENE ...... 235
TABLE 41. PRODUCT QUANTUM YIELDS OF A-(2-BENZYLPHENYL)ACETOPHENONE IN BENZENE ............... 236
TABLE 42. PRODUCT QUANTUM YIELDS OF A-(2-ETHYLPHENYL)PROPIOPHENONE IN BENZENE ................. 237
TABLE 43. PRODUCT QUANTUM YIELDS OF A-(2,4,6-TRIETHYLPHENYL)PROPIOPHENONE IN BENZENE ...... 238
TABLE 44. PRODUCT QUANTUM YIELDS OF A-(2-ETHYLPHENYL)ACETONE IN BENZENE ............................ 239
TABLE 45. PRODUCT QUANTUM YIELDS OF A-MESITYLACETONE IN BENZENE ........................................... 240
TABLE 46. PRODUCT QUANTUM YIELDS OF A-(2,4,6-TRIETHYLPHENYL)ACETONE IN BENZENE ................. 241
TABLE 47. PRODUCT QUANTUM YIELDS OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETOPHENONE IN BENZENE242
TABLE 48. PRODUCT QUANTUM YIELDS OF A-(2-BEN2YLPHENYL)PROPIOPHENONE IN BENZENE ............... 243
TABLE 49. PRODUCT QUANTUM YIELDS OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETONE IN BENZENE .......... 244
TABLE 50. PRODUCT QUANTUM YIELDS OF 2-(2’-(2’,3 ’-DIMETHYL)BUTYL))BENZOPHENONE ................... 245
TABLE 51. QUENCHING OF THE INDANOL FORMATION IN A-(2-ETHYLPHENYL)ACETOPHENONE WITH 2,5-
DIMETHYL-Z ,4-HEXADIENE AT 313 NM IN BENZENE ................................. 246

TABLE 52.

 

 

QUENCHING OF THE INDANOL FORMATION IN A- (2, 4 ,6-TRIETHYLPHENYL) ACETOPHENONE WITH

2, 5- DIMETHYL- 2, 4- HEXADIENE AT 313 NM IN BENZENE .................................................................... 246

TABLE 53.

QUENCHING OF THE INDANOL FORMATION IN A-(2-BENZYLPHENYL)ACETOPHENONE WITH 2,5-

DIMETHYL-2,4-HEXADIENE AT 313 NM IN BENZENE .......................................................................... 247

TABLE 54.

DIMETHYL-2 ,4-HEXADIENE AT 3 I3 NM IN BENZENE .......................................

TABLE 55.

QUENCHING OF THE INDANOL FORMATION IN A-(2-ETHYLPHENYL)PROPIOPHENONE WITH 2,5-
247
QUENCHING OF THE INDANOL FORMATION IN A-(2, 4 ,6-TRIETHYLPHENYL) PROPIOPHENONE WITH

 

2, 5- DIMETHYL-Z, 4-HEXADIENE AT 313 NM IN BENZENE .................................................................... 248

TABLE 56.

QUENCHING OF THE INDANOL FORMATION IN 2'-(2, 3- DIMETHYL-2- -BUTYL)BENZOPHENONE WITH

 

2, 5-DIMETHYL-2, 4- HEXADIENE AT 313 NM IN BENZENE .......................................... 248
TABLE 57. QUENCHING OF THE DIARYLETHANE FORMATION IN A- -(2-ETHYLPHENYL)ACETONE WITH 2, 5-
DIMETHYL-z ,4-l-IEXADIENE AT 313 NM IN BENZENE .......................................................................... 249
TABLE 58. QUENCHING OF THE DIARYLETHANE FORMATION IN A-MESITYLACETONE WITH 2,5-DIMETHYL-
2,4-HEXADIENE AT 313 NM IN BENZENE ............................................................................................. 249
TABLE 59. QUENCHING OF THE DIARYLETHANE FORMATION IN A-(2,4,6-TRISIOPROPYLPHENYL) ACETONE
WITH 2,5-DIMETHYL-2,4-HEXADIENE AT 313 NM IN BENZENE ........................................................... 250

xi

List of Schemes

 

 

 

SCHEME 1. A-CLEAVAGE REACTION ................................................................................................................ 5
SCHEME 2. A-CLEAVAGE OF PIVALOPHENONE ................................................................................................. 5
SCHEME 3. CAGE AND NON-CAGE REACTIONS ................................................................................................ 6
SCHEME 4. A-CLEAVAGE IN CYCLIC KETONES ................................................................................................ 7
SCHEME 5. ORBITAL REQUIREMENTS OF TYPE 11 CLEAVAGE ............... . ......................................................... 10
SCHEME 6. ROLE OF BACK TRANSFER IN DETERMINATION OF QUANTUM EFFICIENCIES ............................... 1 1
SCHEME 7. CONFORMATIONAL, ROTATIONAL AND GROUND STATE CONTROL OF REACTIVITY .................... 12
SCHEME 8. CONFORMATIONAL CONTROL OF REACTIVITY ............................................................................. 12
SCHEME 9. GROUND STATE CONTROL OF REACTIVITY .................................................................................. 13
SCHEME 10. ROTATIONAL CONTROL OF REACTIVITY -. .......................................................... 14
SCHEME 1 1. PHOTOCYCLIZATTON OF 2,4,6-TRIISOPROPYLBENZOPHENONES ................................................. 17
SCHEME 12. BOAT-LIKE TRANSITION STATE FOR HYDROGEN ABSTRACTTON ............................................... 19
SCHEME 13. COMPETITION BETWEEN H-ABSTRACITON AND CYCLIZATION EFFICIENCIES ............................ 21
SCHEME 14. A-HYDROGEN ABSTRACTION IN OTBBP .................................................................................... 22
SCHEME 15. PHOTOBEHAVIOR OF OTAMBP ................................................................................................. 23
SCHEME 16. PHOTOCHEMISTRY OF BENzOIN ETHERS .................................................................................... 29
SCHEME l7. PHOTOCHEMISTRY OF HEXAETHYLBENZIL ................................................................................ 29
SCHEME 18. CRYSTALLINE STATE vs. SOLUTION PHOTOCHEMISTRY ............................................................ 30
SCHEME 19. PHOTOCYCLOADDmON OF BENZALDEHYDE TO CYCLOALKENES .............................................. 35
SCHEME 20. ISC CONTROL OF DIASTEREOSELECTIVITY ................................................................................ 36
SCHEME 21. PHOTOTAUTOMERIZATION OF ENOL TO KETONE ................................................................. ' ...... 37
SCHEME 22. PHOTOBEHAVIOR OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETOPHENONE ...................................... 37
SCHEME 23. CHEMICAL SHIFTS OF METHYLS TRANS AND CIS T0 PHENYL IN FIVE-MEMBERED RINGS ........ 42
SCHEME 24. PHOTOCHEMISTRY OF 1 .............................................................................................................. 43
SCHEME 25. PHOTOCHEMISTRY OF 2 .............................................................................................................. 44
SCHEME 26. PHOTOCHEMISTRY OF 3 .............................................................................................................. 46
SCHEME 27. PHOTOCHEMISTRY OF 4 .............................................................................................................. 48
SCHEME 28. PHOTOBEHAVIOR OF 5 ................................................................................................................ 50
SCHEME 29 ................................................................................................................................ 51
SCHEME 30. PHOTOBEHAVIOR OF 6 ................................................................................................................ 52
SCHEME 31. PHOTOBEHAVIOR OF 7 ................................................................................................................ 54
SCHEME 32. PHOTOCHEMISTRY OF 8 .............................................................................................................. 55
SCHEME 33. PHOTOBEHAVIOR OF 9 ................................................................................................................ 57
SCHEME 34. PHOTOPRODUCTS OF 10 ............................................................................................................. 65
SCHEME 35. PHOTOCHEMISTRY OF 1 1 ............................................................................................................ 66
SCHEME 36. PHOTOBEHAVIOR OF 12 .............................................................................................................. 68
SCHEME 37. PHOTOCHEMISTRY OF 13 ............................................................................................................ 69
SCHEME 38. PHOTOBEHAVIOR OF 14 .............................................................................................................. 73
SCHEME 39. PHOTOCHEMISTRY OF 15 ............................................................................................................ 76
SCHEME 40 ..................................................................................................................................................... 90
SCHEME 41 .................................................................... . ................................................................................ 95
SCHEME 42. LOWEST ENERGY BIRADICAL CONFORMATIONS OF 6 .............................................................. 104
SCHEME 43. REACTTVE GROUND STATE CONFORMATIONS OF 10 ................................................................ 1 15
SCHEME 44 ............................... ................................................................................ 1 19
SCHEME 45 ................................................................................................................................................... 1 l9
SCHEME 46 ................................................................................................................................................... 120
SCHEME 47 ................................................................................................................................................... 123
SCHEME 48 ................................................................................................................................................... 125
SCHEME 49 ................................................................................................................................................... 126

xii

SCHEME 50..

SCHEME 5 l.
SCHEME 52.
SCHEME 53.
SCHEME 54.
SCHEME 55.
SCHEME 56.
SCHEME 57.
SCHEME 58.
SCHEME 59.
SCHEME 60.
SCHEME 61.
SCHEME 62.
SCHEME 63.
SCHEME 64.
SCHEME 65.
SCHEME 66.
SCHEME 67.
SCHEME 68.
SCHEME 69.
SCHEME 70.
SCHEME 71.
SCHEME 72.
SCHEME 73.
SCHEME 74.
SCHEME 75.
SCHEME 76.
SCHEME 77.

 

 

................................................................................................................................................. 127
SYNTHESIS OF A-(2-ETHYLPHENYL)PROPIOPHENONE .............................................................. 132
SYNTHESIS OF A-(2-ETHYLPHENYL)ACETONE .......................................................................... 138
SYNTHESIS OF A-MESITYLACETONE ........................................................................................ 140
SYNTHESIS OF A-(2-BENZYLFHENYL)PROPIOPHENONE ......... - ................... 142
SYNTHESIS OF A-(2,4,6-TRIETHYLPHENYL)-B,B,B-TRIDEUTEROPROPIOPHENONE .................... 145
SYNTHESIS OF A-(2,4,6-TRIETHYLPHENYL)ACETONE .............................................................. 150
SYNTHESIS OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETONE ........................................................ 152
SYNTHESIS OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETOPHENONE ............................................. 155
SYNTHESIS OF o-IERT-BUTYLTRIFLUROACETOPHENONE ......................................................... 157
SYNTHESIS OF 2-(2'-(2',3'-D1METHYL)BUTYL)BENZOPHENONE ................................................ 161
PHOTOPRODUCTS OF A-(2-ETHYLPHENYL)ACETOPHENONE ..................................................... 169
PHOTOPRODUCTS OF A-(2,4,6-TRIETHYLPHENYL)ACETOPHENONE .......................................... 172
PHOTOPRODUCTS OF A-TOLYLPROPIOPHENONE .......................................... .. 176
PHOTOPRODUCTS OF A.(2-ETHYLPHENYL)-B,B,B-TRIDEUTEROPROPIOPHENONE ..................... 178
PHOTOPRODUCTS OF A~(2,4,6-TRIETHYLPHENYL)B,B,B-TRIDEUI'ERO PROPIOPHENONE .......... 183
PHOTOPRODUCTS OF A-(2-BENZYLPHENYL)ACETOPHENONE ................................................... 188
PHOTOPRODUCTS OF A—(2-BENZYLPHENYL)PROPIOPHENONE ................................................. 190
PHOTOPRODUCTS FROM A-MESITYLPROPIOPHENONE .............................................................. 193
PHOTOPRODUCTS OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETOPHENONE ................................... 196
PHOTOCHEMISTRY OF TRIMETHYLSILYLENOL ETHER OF 9 ...................................................... 200
PHOTOPRODUCTS OF A-(2-ETHYLPHENYL)ACETONE ............................................................... 202
PHOTOPRODUCTS OF A-MESITYLACETONE .............................................................................. 206
PHOTOPRODUCTS OF A-(2,4,6-TRIETHYLPHENYL)ACETONE .................................................... 210
PHOTOPRODUCTS OF A-(2,4,6-TRIISOPROPYLPHENYL)ACETONE ............................................. 212
PHOTOPRODUCTS OF O-TERT-BUTYLTRIFLUROACETOPHENONE ............................................... 214
PHOTOPRODUCTS OF o-TERT-AMYLBENZOPHENONE ................................................................ 216
PHOTOPRODUCTS OF 2-(2'-(2',3'-DIMETHYL)BUTYL)BENZOPHENONE ...................................... 218

xiii

OTBBP

OTAMBP

ISC

SOC

nOe

CMC

PTLC

List of Abbreviations

o-tert-Butleenzophenone
o-tert-Amleenzophenone
Intersystem Crossing

Spin-Orbit Coupling

Nuclear Overhauser Enhancement
Critical Micellar Concentration

Preparative Scale Thin Layer Chromatography

xiv

Introduction

Many chemical reactions require the input of considerable energy to proceed. This
energy is usually introduced as heat. Photochemical methods, however, provide an
alternative way to add energy to reactants. The light absorbed by the photoactive portion
of the molecule, the chromophore, provides energy to the system. Absorption of
electromagnetic radiation by a molecule depends on a correspondence between the
radiation energy and the energy of certain molecular transitions. The energy associated
with ultraviolet and visible light is required to excite electrons in molecules. The first step
in a photochemical reaction is excitation of a molecule through absorption of a photon.
Whether this excited molecule leads to a chemical reaction or returns to the original
ground State depends upon competition between various intramolecular and

intermolecular interactions within the system.

81
T" "\
k. . T1
k
hv {i kr

Products
Products

 

 

 

 

Figure 1. Simplified Jablonski Diagram

The photophysical and photochemical processes of molecules can best be
described with the Jablonski diagram (Figure 1).1 Absorption of a photon promotes a
molecule from the ground state to the Singlet excited state. The excited state molecule can

decay to the ground state via emission of light (fluorescence) or radiationless decay. Rate
. . 6 9 -l 5
constants for fluorescence and radiationless decay are on the order of 10 -10 s , and 10 -

s -l , . . . . .
10 s respectively.2 ’3 Photochemical reactions are also pOSSible from the exc1ted Singlet.

The excited Singlet can undergo intersystem crossing to an excited triplet state. Typical

, , 7 II -1
rate constants for intersystem crossmg (kisc) are on the order of 10 -10 s .2’3 ’4 ’5 ‘6 ‘7 The

excited triplet can decay via radiative deactivation (phosphorescence) with a rate
I 6 -l . . .
constant, kp, of 10 —10 s .2 It can also undergo radiationless decay and chemical

reaction. Quenching'of the excited triplet by energy transfer and/or charge transfer can

occur with a rate constant as high as the rate of diffusion in a given solvent
I0 -I -1 s

(<10 M S )..

Photochemistry of the carbonyl group has been a major target of research for
many decades. Aliphatic and aromatic ketones undergo similar photochemical reactions.
However, the excited states leading to these reactions are somewhat different for the two.
The reactive excited state of aliphatic ketones is the n,1t* state. On excitation, an electron
from the oxygen nonbonding orbital is transferred to the 1r*-antibonding orbital of the
carbonyl group, creating an electron deficient oxygen. The Singlet is initially formed, but
. . - - 3 II -I 2,3.4.5.6.7
intersystem crossmg to the triplet occurs With rate constants of 10 -10 s . Both

Sl (lowest excited Singlet) and TI (lowest excited triplet) exhibit reactivity for aliphatic

'r
't

I“

w«..

i...

’l

N)».

.Tm

sob

ketones. The chemical behavior of the n,1t* triplet state is similar to that of an alkoxy
radical. (II—Cleavage, hydrogen abstraction, and charge transfer from an electron donor

are the reactions frequently observed.9 "0 "1

Phenyl ketones have two low lying triplets,
an n,1r* triplet and a 7t,1t* triplet, whose energy levels are affected by ring substituents
and solvents. The 1r,rr* triplet arises from promotion of an electron from a n-bonding to a
m-antibonding orbital. This results in a Shift of electron density from the aromatic 1:-
system to the carbonyl oxygen, generating an electron rich oxygen, and makes the 1r,1t*
triplet much less reactive than the n,rr* triplet. Ketones with a Tt,1t* lowest triplet state do
undergo typical n,1t* triplet reactions, but at a much slower rate, which reflects the

population of the reacting 11,1” State at equilibriumn'” .14

A wide variety of reactions
have been reported in ketone photochemistry. Those relevant to this work are

summarized below.

1. Measurements of Quantum Yields and Excited State Lifetimes

Quantum yields of photoreactions are defined as the molecules of product formed
per photon of light absorbed. Thus, quantum yields can be obtained by measuring the
product concentration and the light absorbed during the course of the reaction. The latter
is usually measured using actinometers, which are compounds with known quantum
efficiencies.

The quantum yield for any photochemical reaction can be expressed as the

product of probabilities. Thus, for a triplet hydrogen abstraction,

(D = cDisc kH TP Br
1/1 = kH + kd

PBr = kI/(kr+kBt)
Equation 1

where (Disc is the intersystem crossing quantum yield, k“ is the rate constant for hydrogen
abstraction, kd is the rate constant for triplet decay other than hydrogen abstraction, r is
the triplet lifetime, and P3, is the probability that the intermediate will go to products. In

the presence of an external quencher 1 decreases and mathematically becomes:

1/1 = kH + k, + kq[Q]
Equation 2

where kq is the bimolecular quenching rate constant. The Stem-Volmer equation is a
mathematical relationship between quantum efficiencies in the absence (<D°) and presence

((1)) of quencher and is written as:

CD°/(D= 1 +qu [Q]
Equation 3

Thus a plot of (D0 / (D versus [Q] Should give a straight line with an intercept of 1 and a
slope of qu. In most cases, the rate of energy transfer quenching by dienes is diffusion
controlled. For example, kq is known to equal 5-6 x 109 M'ls'l in benzene at room

8,15

temperature. Thus, the triplet lifetime can be calculated from the slope of the Stem-

Volmer plot.

II. a—Cleavage reactions

Photoexcited carbonyl compounds can undergo a-cleavage reactions (Scheme 1).
These reactions are commonly referred to as Norrish type-I reactions of the carbonyl

16
compounds.

0 O
R hV I o . . . . .
__.. O + R _. Products (disproportionation, coupling)

Scheme 1. a-Cleavage Reaction
The reaction's rate constant is dependent on the nature of the excited state, the
relative stability of the alkyl radicals formed, and the degree of steric crowding in the
reactant ketone. The reaction has been generally recognized to occur from an n,1t* excited
state. The cleavage occurs due to the weakening of the (Jr-carbon bond by overlap with

l7.l8,l9

the vacant n orbital which also happens in alkoxy radicals. When the excited state

configuration is 1r,1r*, no such overlap is possible and the reaction does not occur.
Pivalophenone, which has a lowest n,1r* triplet, cleaves with a rate constant of 107 8'],
whereas p-methoxypivalophenone, with a It,1t* lowest triplet, cleaves much slower with a
rate constant on order of 105 s'I .20

O O

O .. 0 '*

Pivalophenone

Scheme 2. a-Cleavage of Pivalophenone

The (II—bond that produces the more stable carbon radical cleaves preferentially in
unsymmetrically substituted ketones. Lewis has Shown that the products obtained from
the a—cleavage of ketones can be accounted for according to a mechanism shown in
Scheme 3.21 The resulting radicals can recouple or disproportionate in the cage or diffuse

apart and be trapped by other radicals, solvent or additives.

T) /
Ph/“>< Ph Ph/l KP h) _..\[/ +PhCHO

 

 

PhCOCOPh + Eh I[ } Ph PhCHO+RSSR +Y

Ph

Scheme 3.8Cage and Non-cage Reactions

Baum22 reported a similar study with 2-phenyl-1-indanone and 2,6-diphenyl-1-
indanone. Although 2-phenyl-l-indanone cleaves efficiently to isomeric products, 2,6-
diphenyl-l-indanone affords little product. This observation is consistent with the fact
that 2-phenyl-1-indanone has an n,1r* lowest energy triplet and 2,6-diphenyl-l-indanone

has a 1r,1r* lowest energy triplet.

O
R R CHO
hv
O. .. #(w
— Ph

R= H, 2-phenyl- l -indanone
R= Ph, 2,6-diphenyl-l-indanone

Scheme 4. (II-Cleavage in Cyclic Ketones

The photochemical ring opening reactions of 2-hydroxyindan-1-ones have been
reported to involve an initial Norrish type I cleavage followed by a 1,4-hydrogen transfer
from a benzylic carbon.23 ’24 The possibility of 1,6-hydrogen transfer from the OH was
ruled out when photolysis in methanol-d4 resulted in no deuterium incorporation in the
aldehyde.

In aliphatic ketones, where both singlet and triplet states can be populated, the

25 .26
Turro and co-workers have

triplet cleaves about 100 times faster than the singlet.
estimated the n,1r* singlet and triplet reactivities towards a-cleavage in several cyclic
ketones. Their experimental results indicate that the triplet rate constant was larger than

-I 25

5x1010 5", while the singlet rate constant was smaller than 2.5 x 108 s . Yang has

reported that the triplet state of di-tert-butyl ketone cleaves with a rate constant of 7-

-1

9x109 S , while the cleavage rate constant for the Singlet is only 6x107s'l.26 Phenyl
ketones undergo (ii-cleavage at much Slower rates than aliphatic ketones. For example,
triplet aliphatic t-butyl ketones a—cleave about 4000 times faster than triplet

pivalophenone.27

Electron donating groups on the a—phenyl ring enhance the reaction, indicating an
early transition state with some ionic character.21 Other a—substituents also Speed up the
reaction, however, the rate constant for the reaction is dependent on the steric congestion
in the ground state and was found to be independent of the stability of the resulting

. 21
radicals.

 

III. Hydrogen Abstraction

Photoexcited carbonyl compounds may undergo a characteristic hydrogen shift to

the carbonyl oxygen from hydrogen donors.”29

This process, known as hydrogen
abstraction, can Occur between an excited carbonyl and an external donor molecule
(intermolecular hydrogen abstraction) or internally within the same molecule
(intramolecular hydrogen abstraction). AS for the a—cleavage reaction, hydrogen
abstraction may occur from both Singlet and triplet states in aliphatic ketones whereas the
abstraction process occurs solely from the triplet excited state in the aromatic ketones.
For aromatic ketones, the intersystem crossing of the initially formed Singlet excited state
is so fast (~10ll s") that reactions Of the S, state are usually not observed. 30

The reactive excited state for hydrogen abstraction is the n,1r* state. Carbonyl

compounds with a It,1t* lowest excited state abstract hydrogen at much slower rates (from

a thermally populated n,1t* state, or from the 1t,7r* state)”14 This inefficiency is

attributed to a relatively high electron density on the oXygen atom in the 1r,n* state. By
comparison, the oxygen atom in the n,1t* state is more reactive toward hydrogen donors
because of its radical like character. Hydrogen abstractions by triplet carbonyls are
similar to those by alkoxy radicals.“ The n,7r* triplets, like alkoxy radicals have such a
high electron demand that the transition states for hydrogen transfer are stabilized by
charge transfer. Therefore, electron withdrawing groups near reactive hydrogens Slow
down the reaction.”48
Intramolecular hydrogen abstraction is the subject of this research and the
material that follows will focus on this subject. Intramolecular hydrogen abstraction from
the y—carbon atom is favored but will occur from other positions when there are no
hydrogens at the 7 position and the molecular conformations allow other Sites to come
into close proximity to the excited carbonyl group. In acyclic systems the rate of
abstraction from these Sites is intrinSically lower Since the transition state involves more
strain and there is a lower probability that the molecule will attain the required
conformation.32 '48
The y-hydrogen abstraction yields a 1,4-biradical. Depending on the conformation

of the initially formed 1,4-biradical, two different pathways are possible: (1) If the p
orbitals of the radical centers can overlap, a cyclobutanol is the product. (2) If the p
orbitals of the radical centers are parallel to the B-bond, this bond will cleave to yield an
enol and an alkene (Scheme 5). These cyclization and cleavage reactions are termed the

Norrish Type II reaction. The requirement that the orbitals be parallel to the B-bond is

equivalent to the need for a planar transition state. This is illustrated in the reaction of a-

10

cyclohexyl-cyclohexanone in which the a,B-carbon-carbon bond must be axial in both
rings for a cleavage conformation and, because of the limitations on this conformation,

the cyclization process is preferred from both Singlet and triplet states.30 (Scheme 5)

hv

 

 

OH OH

 

Cyclization [Cleavage

M

Scheme 5. Orbital Requirements of Type II cleavage

OH

 

 

 

 

One of the mOSt important reactions of the intermediate biradicals is
disproportionation to give back the starting ketone or back transfer. Quantum efficiencies
for cyclization and cleavage are determined by the extent of the back transfer (Scheme 6).

Quantum yields in Lewis base solvents are generally higher than in hydrocarbons
Since the former can hydrogen bond to the resulting hydroxybiradical and prevent the

back transfer.33

11

O
M ' hV J\/\ k /“\/\
Ph CHZR ——_’ Ph CHzR'A.’ Ph CHZR‘

Ph OH ¢Cyc=(¢isc-kH)TPCyc
LCHR' PCYC= kCyc/(kCyc+k-H+ kCleav)

kCleav kw RH: k-H/(kCy¢+kCle.av'+'k-H)
h - (D = Quantum Yield
OH

* + H2C=CHR' ELTQH r= Lifetime of the triplet
Ph CH2 P= probability of any

R.
biradical reaction

1”?

Scheme 6. Role of Back Transfer in Determination of Quantum Efficiencies

A. Conformational Control of Photoreactivity

The efficiency of hydrogen abstraction is dependent on the preferred ground state
geometry, particularly since excited states can be very Short-lived. Intrarnolecular
hydrogen abstraction requires the carbonyl oxygen and the abstractable hydrogen to
approach each other in such a way that proper orbital overlap and reaction can occur. This
requirement makes photochemical intramolecular hydrogen abstractions sensitive to
conformational equilibria, since competitive photochemical reactions can occur at rates
faster than conformational motions.34 The competition between conformational change,
reaction, and decay (Scheme 7) provides three boundary conditions: 35 (1)
Conformational equilibrium (kl, k_, >> k,, kd) (2) Ground state control (kl, k,l << k,, kd)

(3) Rotational control (k1~ kd, k,,< k,).34

12

x Y *x Y
h .

k-l k1

 

 

 

V l

 

)(vvvvvvvvvver hv . X Y kd Decay

 

 

 

Scheme 7. Conformational, Rotational and Ground State Control of Reactivity

Wagner and Meador have reported that a—(o-alkylphenyl)acetophenones undergo
efficient 5-hydrogen abstraction followed by cyclization to yield 2-indanols.36 In their
investigation, the rate of hydrogen abstraction by triplet a-mesitylacetophenone was
found to be 7 times faster than that of triplet a—(o-tolyl)acetophenone. The slower
hydrogen abstraction rate of or—(o-tolyl)acetophenone was attributed to a conformational

equilibrium between the reactive syn and the unreactive anti conformers (Scheme 8).

 

Anti (unreactive) Syn (reactive)

 

Scheme 8. Conformational Control of Reactivity

13

In molecules where conformational changes are comparable or Slower than
photoreactions, either ground state control or rotational control may occur.

Several benzoylcyclohexane derivatives have provided the most clear-cut
examples of ground state control in photoreactions. Lewis37 investigated conformational
effects in the photochemistry of l-methylcyclohexyl phenyl ketone and a number of
substituted analogs. Lewis found that for l-methylcyclohexyl phenyl ketone, there exist
two different ketone triplets, each leading to different photoproducts (Scheme 9). The
ketone conformer with the benzoyl group in an axial position undergoes y-hydrogen
abstraction followed by cyclization to the corresponding 6-hydroxy-l-methyl-6-
phenylbicyclo-[3.1.l]-heptane. The ketone conformer having the benzoyl group in an
equatorial position cannot undergo hydrogen abstraction Since the carbonyl group is
oriented away from those hydrogens. Instead, it undergoes acyl cleavage giving rise to
benzaldehyde as well as other products expected from the benzoyl and 1-

methylcyclohexyl radicals.
0 Ph 0 Ph . Ph H O ph
9: H ‘ 1 bp
.. CH3 “V \CH f , CH3 , ,. CH3
3 f V—

Scheme 9. Ground State Control of Reactivity

 

 

 

 

 

14

Lewis found that the ratio of the products from the two different pathways is entirely
dependent upon the ground state population of each ketone conformer.
An example of rotational control of photoreactivity is provided in the

35 33 . .
The anti rotamer is much less

photoenolization of o-alkylphenylketones (Scheme 10).
reactive than the syn rotamer. The lack of an H/D isotope effect on the rate of decay of

the anti triplet led to the conclusion that the rate determining step was bond rotation and

not hydrogen abstraction.35

O

*3
hV / I R
CHZR ICHzR: CH2 R \ CHZR

 

. H |OH
/ / /’ \\
HR \ “CHR

Scheme 10. Rotational Control of Reactivity

B. Orientational Requirements of Hydrogen Abstraction

One unresolved point that has been subject of much debate during the past twenty
years has been the preferred transition state geometry for hydrogen abstraction process. In
1968, Turro reported that irradiation of cyclohexane solutions of cis- and trans-2m-
propyl-4-t-butylcyclohexanones results in strikingly different photochemistry (Figure

2).39 Photolysis of the cis precursor resulted in the formation of 4-t-butylcyclohexanone,

15

while photolysis of the trans isomer gave the Cis compound as the major product,
presumably as the result of (II-cleavage followed by reclosure with epimerization. Based
on these results, Turro suggested that the striking contrast in the photochemistry of cis
and trans isomers results from a stereoelectronic requirement for the Type II reaction,
namely that the hydrogen on the y—carbon to be extracted must be directed toward the

half-vacant n orbital of the carbonyl oxygen atom.39

   

C is Trans
Figure 2

Scheffer has studied the Type II reaction in the crystalline state where the reactant

geometry is fixed and measurable by x-ray diffraction methods.‘OS

d
>120 ,2 m

X -0...

d S 2713 cu: 0° v= 90-1200 1] = 180°
Figure 3. Orientational Requirements for H-Abstraction
In analyzing their reactivity, he considered the following ground state parameters,

as depicted in Figure 3, to be the most important in determining the reactivity: d, the

16

distance between 0 and H; r], the O-H-C angle, v, the C=O-H angle; and a), the dihedral
angle that the O-H vector makes with respect to the nodal plane of the carbonyl pi
system. In several ketones, for which x-ray crystal structures were obtained, the value of
d ranged from 2.3-3.1 A, n from 85-120°, v from 74-103°, and a) from 0-620.”105 ‘40 ‘4'

Scheffer suggests the theoretically “ideal” values for these parameters to be those shown
in Figure 3. The distance of 2.7 A is the sum of the H and 0 van der Waals radii. Scheffer
points that when hydrogen is this close in the ground State, minimal molecular motion is
required for hydrogen abstraction in the crystal. Molecular flexibility can, however, allow
hydrogen abstraction to occur at longer distances. The deviations from ideality in case of
n and a) have long been known from the reactivity of many steroidal ketones. ”’48

Morrison and coworkers reported ab initio studies (3-210 basis set) for hydrogen
abstraction from methane by triplet formaldehyde.42 The calculated saddle point for the
reaction had the following parameters: (1: 1.18 A, V: 109°, (0:90, n=176°.

Sugiyama has reported that in some bridged polycyclic ketones (Figure 4),
photolysis results in no hydrogen abstraction, although the hydrogens are extremely close
to the carbonyl oxygen.‘13 He attributed this to the unfavorable dihedral angle between the
hydrogens and the C-C=O plane. An alternative explanation could be that the abstraction
is indeed occurring, but the biradical does not cyclize and instead disproportionates to the
Starting material. This seems reasonable since cyclization will put additional strain on an

already strained ring system.

17

R = H, OH
Figure 4. Effect of Dihedral Angle on Reactivity

Photochemical studies of solid complexes of desoxycholic acid and acetophenone
derivatives provide examples of intermolecular hydrogen abstraction from the
perpendicular direction of the carbonyl plane, but it was concluded that molecular
motions within the crystal lattice permitted approach of the reactive hydrogen to the locus

of the n orbital of the excited ketone.44

Matsuura suggested. that photocyclization of 2,4,6-triisopropylbenzophenones

(Scheme 11), where abstractable hydrogens lie between 55-600 out of the plane of the
carbonyl group, occurs from the 1r,1t* state.45 This was because the reaction from the n,1r*
state requires rotation about several bonds and therefore, is topochemically unfavorable in

the solid state.

 

J\ h .J\OH LOH C'l' .
%% ”WI 5 © ; \. _L.
\2 ' \/ ’ |/J

Scheme 11. Photocyclization of 2,4,6-Triisopropylbenzophenones

Sauers and co-workers designed polycylic ketones that contain hydrogen atoms

fixed in the plane of the 1: system (Figure 5) with the aim of setting limits on reactivity

18

based on out of plane angles.46 They reported that even when theoretical models did not
reveal any barriers attributable to unusual steric strain, no reaction occurred. The short
triplet lifetimes of these ketones were attributed to a reversible Norrish type I cleavage
that generates very Short lived biradicals.47

 

 

 

 

 

 

 

 

 

 

 

 

A. R = H, Phenyl B. X = H. CH3,C1, Br

Figure 5. Effect of Dihedral Angle on Reactivity

Wagner suggested that the ease of 1,5-hydrogen transfers in acyclic systems
reflects primarily a torsion free, chair-like, six-membered cyclic transition state such that
the C-H-O angle is tetrahedral;48 This angle is much less than the linear arrangement
calculated by theoretical models. It was also proposed that the torsional strain present in
the cycloheptane-like transition state for 1,6-hydrogen transfers is responsible for the
slower rate of O—hydrogen abstraction in straight chain systems. Wagner also suggested

that coplanar hydrogen abstraction is not a strict requirement for the Type II process and

proposed a coszco dependence for abstraction.l

 

19

Scheffer has reported a boat rather than a chair transition state for hydrogen
abstraction in a few cases (Scheme 12). 49 His studies further reinforced the notion that

hydrogen and the carbonyl need not be coplanar for the abstraction process to take place.

H
O
hv ° OH
——'> ____, Products
Ar . '
Ar

H-

H . H, 0 Projection down the equatorial carbon-carbon bond
of ketone

Scheme 12. Boat-Like Transition State for Hydrogen Abstraction

Houk noted that a chair-like cyclohexane transition state requires a severely
nonlinear geometry for hydrogen transfer.50 He carried out both ab initio molecular
orbital calculations and force field modeling which predict the six-membered transition
structure for y—hydrogen abstraction (butoxy radical) resembles a five membered ring of
heavy atoms, having an envelope Shape like that of a cyclopentane, but with one long

bond (2.5 A) between Ca and O.50 The seven-membered cyclic transition structure for 6—

hydrogen abstraction (pentoxy radical) also had a chair form much like that of
cyclohexane, but with one long bond. In both transition structures the CH0 angle was
nearly linear. Based on their calculations, Houk and co-workers have suggested that the
preference for a six-membered over a seven-membered transition state iS the result of a
more favorable entropy of activation for the six-membered transition state.50 Similar
transition state geometries were calculated for the y- and 5—hydrogen abstractions of

triplet butanal and pentanal, respectively.“

20

 

Sauers and co-workers found a correlation between the overall reaction and the
transition state steric energy. Using computational methods, they calculated the transition
structure energies for intramolecular hydrogen abstraction at 7 vs. 8 positions for triplet

52 '53 In the lowest energy conformation of cyclodecanone, a y—hydrogen

cyclodecanone.
lies close (2.54 A) to the carbonyl group. The e-hydrogen, on the other hand, is not only

remote (4.12 A), but is on the wrong side of the molecule. However, another low energy

conformation was found in which the e-hydrogen lies close (2.48 A) to the carbonyl

moiety.53 The out of plane angles are 560 and 90.20 for the y and e hydrogens in the two
structures, respectively. lrradiations in cyclohexane are reported to yield only lO-decalols,
products of e-hydrogen abstraction. Computed transition structure energies Show a clear

preference for reaction via a 6-membered ring, over an 8-membered ring.

 

Static Energy-21.4 keallmol Static Energy=23.8 keel/mot

The reason for this apparent paradox lies in the ratio of cyclization vs. disproportionation

rates, since there would be a large difference in ease of formation of the two ring systems:

21

decalin vs. bicyclo[6.2.0]decane (Scheme 13).53 This hypothesis was confirmed with the
observation that irradiation in tert-butanol produced 1-hydroxybicyclo[6.2.0]decane as
the major product. This is due to stabilization of biradical by H-bonding to the solvent

which will increase the biradical lifetime and the amount of cyclization.

 

OH 0*3 OH
.. —>'“
H
H k-8 'hv
k-v
kccyc O kycyc
0..

OH

Scheme 13. Competition Between H-Abstraction and Cyclization Efficiencies

The above mentioned studies Show that in most cases the transition state for
hydrogen abstraction deviates from ideality. Furthermore, the dependence of reactivity on

the value of a) is not clearly understood. This point will be addressed later in this thesis.

C. S-Hydrogen Abstraction

Intrarnolecular hydrogen abstraction by the carbonyl function occurs from sites
other than the y—position when this position has no hydrogens or when the chemical or
geometrical features of the molecule allow for effective competition from other
positions. In 6—methoxy-valerophenone, for example, B—hydrogen abstraction has the
same rate as the y—abstraction due to activation of the 5—position and deactivation of the

y-position by the methoxy group.30 The biradicals produced from these 5-abstractions,

22

however, cannot undergo simple cleavage to give electron paired products and in some
cases cyclize very efficiently.

Wagner reports that irradiation of o-tert-butylbenzophenone (OTBBP) as a solid
or in solution results in its quantitative cyclization to 1-phenyl-3,3-dimethyl-l-
indanol.54 ’55 ’56 A large solvent effect was also reported on the quantum efficiency and
the lifetime of the 1,5-biradical (Scheme 14).

CH3 '

“304,0 0 .
es."

     

k... > 109 M'1 S'1 at 25°; Ea: 2.5 kcal/mole ; log A= 10.6
biradical lifetime = 43 ns in methanol, 4ns in toluene
(”benzene: 0-04 mmethanol= 1-00

Scheme 14. S-Hydrogen Abstraction in OTBBP

The large value of kH for OTBBP is attributed to an ideal conformation for
hydrogen abstraction. The x-ray structure Shows that one of the tert-butyl hydrogens is
2.46 A from the carbonyl oxygen (HA, (1): 40°), while another is 2.67 A away (H3,

m=90°).

 

23

In order to determine which hydrogen is attacked, an unsymmetrical analog, 0-
tert-amylbenzophenone was investigated. o-tert-Amylbenzophenone (OTAMBP) was
reported to yield a 60:40 ratio for hydrogen abstraction from methyl (1E and 12) and
ethyl (2E and 22) groups of the tert—amyl unit when irradiated in benzene at ambient
temperatures (Scheme 15).57 Furthermore, solid state irradiation of OTABP resulted in

abstraction from ethyl and methyl positions at a ratio of 70:30.

 

Scheme 15. Photobehavior of OTAMBP

This was an interesting result Since the primary and secondary hydrogens in
OTABP adopt different positions in the crystal. The x-ray structure Shows the closest
ethyl hydrogen is 2.63A from the oxygen (co= 45°), while the methyl hydrogen is 2.53A

away but with a different dihedral angle (m=95°).

 

24

,The abstraction of methyl hydrogens in the crystal is engaging Since theoretically these
hydrogens should not be abstracted.

It was mentioned earlier that a—(o-alkylphenyl)acetophenones undergo efficient
cyclization to 2-indanols. Introduction of an a-substituent not only decreases the
efficiency of indanol formation but also introduces (at-cleavage as an alternative pathway
for triplet relaxation (Table 1).58

This phenomenon was explained in terms of the starting geometry of ketones. In
the unsubstituted acetophenones, the most stable conformer is the one with the a-aryl
group eclipsing the carbonyl. This geometry is very close to the reactive geometry. For
the a-substituted acetophenones, however, the a-alkyl substitutent eclipses the carbonyl
and the a-aryl group is twisted away, thus creating a poor geometry for hydrogen
abstraction. As Shown in Table 1, as the rate of hydrogen abstraction drops, due to a poor

starting geometry, reactions such as a-cleavage begin to compete.

Table l. a-Substituent Effect on o-Tolylacetophenone Derivatives

 

 

 

 

 

 

Ketone chm e..." III, 108 SI
a-(o-Tolyl)acetophenone 1 .0 0 1 .2
a-(o-Tolyl)propiophenone 0.05 0.28 0.6
a-(o-Tolyl)isobutyrophenone 0 0.38 0.5
a-(o—Tolyl)valerophenone 0.014 0.032l 2 .2
0.34b

 

 

 

 

 

a) Type I cleavage b) Type II cleavage

25

D. Nature of the Excited State- Singlet vs. Triplet

One of the most intriguing questions in organic photochemistry is whether the
differences in Spin multiplicity between singlet and triplet states will be reflected in their
reactivity in primary photochemical processes. Yang has shown that in aliphatic ketones
the rate of cleavage from the triplet is about 100 times faster than the Singlet.26
Dialkylketones are known to undergo hydrogen abstraction in both the T, and S.

59 ,60 .28
states.

Photolysis of the optically active ketone (S)-(+)-5-methyl-2-heptanone
Showed that photoracemization occurs from the triplet state, suggesting the existence of a
triplet biradical sufficiently long lived to allow racemization at the y—carbon.“ The
results obtained with the optically active ketone shOwed that the total quantum yield of
observed events from T1 is only 0.14.61 Since (Disc was determined to be 0.11 and the
quantum yield for reaction from S, is 0.07, the remaining quantum yield of 0.79 must
represent non radiative decay from S,.‘51 This decay appears to lead to no racemization
and is not affected by changes in the solvent, which implies that if it does involve
formation of a Singlet biradical and subsequent back hydrogen transfer, then the biradical
must be extremely short-lived. Stephenson, et al., have also presented evidence which is
2

consistent with the intermediacy of a singlet biradical in the type II reaction.‘5

It has also been suggested that the type II reaction from 81 state may occur via a

concerted pathway.28 Heller has proposed that the electronic energy might be transferred

into vibrational stretching energy of a C-H bond, with further partitioning into a pair of

26

radicals (or biradical) or to a relaxed ground state.63 Hammond has also postulated that
chemical reactions of the excited states are special forms of radiationless decay.64

Salem has calculated the activation energies and surface crossings for singlet and
triplet state hydrogen abstractions.65 He showed that Simple symmetry considerations
indicate that the n,rr* singlet of the carbonyl correlates with the Singlet diradical product,
whereas the ground state correlates with a zwitterionic species.65 Since the plane of
symmetry is not maintained in most hydrogen abstractions, an avoided crossing between
the excited and ground state surfaces occur (Figure 6). Hydrogen abstraction therefore
requires a radiationless decay which can occur easiest at the point of the smallest energy

11.65

difference between the two surfaces. Conversion of the electronic energy into

vibrational energy populates the ground state at a maximum, from which relaxation to

diradical product or to ground state reactant can occur.”65

In other words, Singlet
hydrogen abstraction is inherently inefficient.

Scaiano et al. have studied fluorescence quenching of acetone by several
hydrogen donors.66 They report the excited singlet of acetone to be 2-10 times more
reactive than the triplet toward hydrogen donors. They have ascribed this to a more
exothermic reaction from the singlet (singlet being higher in energy than triplet) which
results in a lower activation energy for hydrogen abstraction. Furthermore, the lower
quantum yield for product formation from the singlet relative to triplet was attributed to a
lower efficiency of photoreduction from the singlet, i.e., the actual rate of transfer for the

60,63

hydrogen atom to the excited singlet is lower than in the triplet. The authors attribute

27

this inefficiency to deactivation of the excited state to yield the reactants from an avoided

crossing (Figure 6 ) before a radical pair is reached.

 

Correlation Diagram [x Y]

 

 

0
A + H-SnBu; A + .SIIBII3

Figure 6. Correlation Diagram

 

 

 

It was concluded that the interaction of the singlets with hydrogen donors is not a
chemical reaction but a physical quenching mechanism, where the hydrogen donor causes
deactivation by accepting part of the electronic excitation energy as vibrational energy

. . . 60.65
and promoting internal conversron from S, to SO. '

Turro recently reported that a—(o-tolyl)acetones undergo S-hydrogen abstraction
followed by cyclization to yield 2-indanols.67 Quenching studies indicate that O-hydrogen
abstraction occurs from the singlet while a-cleavage occurs form the triplet. The rate

constants of hydrogen abstraction and intersystem crossing from the singlet in tolylbenzyl

28

ketone were reported to be 2 x109 and 5 x 108 s", respectively.67 a-(o-
Tolyl)acetophenone, in contrast, does not cleave but undergoes an efficient (<D=1.0) 5-
hydrogen abstraction followed by cyclization from the triplet.87 The rate constant for
intramolecular hydrogen abstraction of a-(o-tolyl)acetophenone was reported to be

1.6x108 3",” ten-times lower that the singlet abstraction rate reported by Turrom.

 

 

R = Me, 06H. ,, CHzPh

E. Effect of Environment

Turro has studied the photochemistry of a,or-dimethylvalerophenone in several
zeolites.68 Product distribution varied depending on the zeolite cavity size. Type I
cleavage is the main photoreaction when the cavities are too small to allow
conformational changes necessary for the Type II reaction. (The cage effect precludes
observation of Type I products unless the resulting radicals rearrange or disproportionate
while coupling.)

Turro has also studied the photochemistry of a—(o-tolyl)acetones in aqueous
surfactant solution.67 He has Shown an increase in cyclization product (indanol) yields in

micelles compared to solution. This is due to the well-known cage effect.8|

29

DeMayo studied the photochemistry of benzoin ethers, which only a-cleave in

solution, on Silica.69 He reported an 85:15 ratio of Type 1/ Type 11 products and attributed

this to a more reactive ketone geometry and reversibility of cleavage due to poor

translational mobility on the Silica surface. (Scheme 16)

 

 

 

H‘ OCHR2

Scheme 16. Photochemistry of Benzoin Ethers

The crystalline and amorphous solid states can provide unique behavior and
product stereoselectivity. Wagner and coworkers have reported that irradiation of solid

2,4,6,2’,4’,6’-hexaethylbenzil (Scheme 17) has resulted in a three-fold ZzE increase over

. . 70
solution chemistry.

 

Benzene 2

Solid 5

Scheme 17. Photochemistry of Hexaethylbenzil

30

Perhaps, the most striking results in crystalline state photochemistry can be found
in Scheffer’s work. He has shown that when a compound crystallizes in a chiral space
group the crystalline state irradiation, in most cases, will result in high enantio- and/or
diastereoselective photoproducts. For example, the achiral ketone or—(3 -methyladamant-
1-yl)acetophenone crystallizes in a chiral space group.71 Irradiation in crystal results in a
70% yield of a single cyclobutanol in 82% enantiomeric excess with the configuration
depending on the configuration of crystal. The solution photochemistry, however, results

in a racemic mixture of products (Scheme 18).72 ’73

Ar OH
H3C ,,

Solid Benzene

 

 

 

 

Scheme 18. Crystalline State vs. Solution Photochemistry

F. Biradical Lifetime

Triplet biradicals must undergo intersystem crossing (ISC) to form singlet
products. The rate of triplet biradical decay is thus determined by the rate of ISC, since
the chemical reactions of the singlet biradicals presumably are so fast that ISC is
effectively irreversible. Scaiano has postulated that singlet biradicals maintain
conformational memory of their triplet precursor and undergo no conformational change
because they react so rapidly.74 The long lifetimes of triplet biradicals, coupled with
generally fast bond rotations, assure that the biradicals usually attain conformational

equilibrium before ISC. Different biradical conformations may or may not have the same

Ann
‘Ikil

[Ii

’3,
in

3‘

1.1

11“

3.

\fr:

31

ISC rate. Several interesting questions can thus be raised. What causes ISC? What
conformational factors enhance the rate of ISC? When does ISC occur?

Salem and Rowland proposed that three factors are important in determining the
ISC rates. These include: orthogonality of the axes of the two p orbitals, distance between
two biradical centers and ionic (zwitterionic) character of the singlet state.75 These factors
influence spin-orbit coupling which is the predominant cause of ISC in short biradicals.

Recently Michl has performed calculations similar to those of Salem and Rowland
to determine the factors that result in Spin-orbit coupling (SOC).76 His results show that
in order for SOC between singlet and triplet to be large, (a) the most localized orthogonal
orbitals A and B singly occupied in triplet must interact covalently through a non-zero
resonance integral and/or be sufficiently different in energy for one to have electron
occupancy near two in the Singlet (b) the biradical contains one or more atoms (heavier
than hydrogen) at which one p orbital contributes to A and another to B (through bond
contributions) and (c) the contributions from these p orbitals must add rather than cancel.

Scaiano has studied solvent effects on biradical lifetimes. Lewis bases tend to
increase the quantum yields of product formation in hydroxy biradicals.77 It was
interesting to see whether a lifetime increase would parallel an increase in quantum yield
due to suppression of a major chemical path, namely disproportionation back to Starting
ketone. Scaiano, however, showed that lifetime and quantum yield increases are not
Correlated.78 For example, the lifetimes of y-methylvalerophenone in wet acetonitrile79
(76 ns) and pyridine (121 ns) differ by almost a factor of two, while the quantum yield for

PFOduct formatiOn remains essentially unity. Similarly, 2% water in acetonitrile is

32

sufficient to achieve or closely approach the maximum quantum yield of unity, while
lifetimes keep increasing until the concentration of water reaches ~20%.79

Wagner has proposed that the concept of “conformational memory” in singlet
biradicals is only relevant in 1,4-biradicals since they can form products from most
conformations. He has suggested that for 1,5- and longer biradicals, ISC and the chemical
reaction (cyclization) are coupled.80 Both singlet and triplet surfaces rise in energy as
movement along the reaction coordinate develops electronic and steric strain. The singlet
surface, however, is soon stabilized by the developing bond while the triplet keeps rising
in energy. This will lead to surface crossing at points that represent low activation
energies (Graph 1). Since-the biradical ends approach each other as the reaction proceeds,
the ISC at this point benefits from large spin-orbit interactions as well as state

degeneracy.

ENERGY

 

 

 

reaction coordinate
Graph 1. Triplet-Singlet Interconversion

Turro suggests that spin multiplicity cannot change during the elementary

chemical step of bond formation or bond cleavage because the rate of spin motion is too

33

slow relative to the time scale for an elementary step.81 He indicates that hyperfine and
exchange interactions are important factors leading to ISC in (ii-cleavage reactions and
that when the two radical centers are close, strong exchange interactions inhibit spin
inversions.

Closs argued that a triplet biradical goes through a large number of conformations
in which triplet and singlet are nearly degenerate and its wave function is a rapidly
oscillating mixture of singlet and triplet character, with triplet dominant at all times.82
He proposed that ISC will take place only when the biradical reaches a geometry in
which two surfaces separate in energy, with a probability given by the average weight of
singlet character in the wave function.

Michl’s calculations suggest that SOC will be strong in those geometries in which
there is a significant covalent interaction between the two radical centers.76 This
interaction stabilizes SO and destabilizes T1. He suggests that a small but a non-zero
activation energy is needed fOr the triplet to reach the best geometries for ISC and that
after ISC the molecule should find itself part way down a steep path in the So surface
leading to products. He thus concludes that ISC in triplet biradicals Should be concerted
with the formation of a new bond.76

Wagner has also suggested that if ISC occurs discretely, the solvent and structural
effects at early stages of reaction can be treated as entropic factors.80 For example,

lifetime increase in hydroxybiradicals in the presence of Lewis bases can be explained in

terms of a biradical having a lower probability of finding an ISC path since a major path

34

for reaction and ISC has been eliminated. Thus, ISC is disfavored entropically and

lifetime increases.

G. Diastereoselectivity

Unlike singlet reactions, pure steric arguments alone can not explain or predict
product stereoselectivities in triplet reactions. Triplets must first intersystem cross to the
singlet surface before they can form products. An interesting question can be raised. Do
bond rotations occur after ISC and before product formation or does the singlet react so
fast that it does not undergo any conformational change from its triplet precursor? Since
rate constants for Singlet biradical reactions have not been measured, one cannot answer
this question with any degree of certainty. However, most investigators have ignored
bond rotations in the singlet biradical and have assumed that product stereoselectivities
are determined on the triplet surface. Even with such an approximation, prediction of
product stereoselectivities from the triplet surface is not trivial Since one must also
consider ISC. It was mentioned earlier that different biradical conformations may have
different ISC rates. Thus one must consider both the population of various conformers
and their relative intersystem crossing rates to address product stereoselectivities.
Griesbeck has recently attempted to attribute the observed diastereoselectivities in 2+2
photocycloaddition of benzaldehyde to cyclic olefins in terms of relative rates of ISC

. . . 83.84
from various reactive conformations (Scheme 19).

By excluding non-reactive
conformers (although the author doesn’t mention this point), he assumes ISC to be

coupled to the reaction, in agreement with Wagner, Closs and Michl. Griesbeck has

35

observed good endo selectivity between aromatic aldehydes and unsubstituted

cycloalkenes while methyl groups at position 1 or 2 on the cycloalkene lower the amount

of endo oxetane.

The biradical conformer’s A and B (Scheme 20) were considered in the reaction

between benzaldehyde and cycloalkenes, with conformer A, which forms the endo

product, being more populated due to fewer steric interactions.

Table 2. Diastereoselectivity in Photocycloaddition of Benzaldehyde to Cycloalkenes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

X R, R2 Endo/Exoa
CH2 H H 61 :39
CH2 CH3 H 16:94

O H H 88: 12

0 CH3 H 65:35

a) For the major product only
R2 R2 R2 Ph
PhCHO fl—O
\ R 11" r X W—k + / O
I
X Ph X i

R2 R2

Major Minor

Scheme 19. Photocycloaddition of Benzaldehyde to cycloalkenes

36

Methyl substitution at position 1, however, forces the oxygen bridge to twist
toward the middle of the cycloalkene ring due to steric interactions between the methyl
and phenyl or hydrogen of the aldehyde. Thus, conformer D, being more populated due to
fewer steric interactions, leads to an increase in the amount of exo product. The author
emphasizes that these conformers are not real minima on the triplet surface and that they
merely represent geometries for rapid ISC, due to orthogonality of the p-orbitals at radical

centers.

Ph H
Q *FE’ flH+Q§prh

El'ldO EXO
H 0 ph O
U 6.6.6 bé
X CH3 hv Ph CH3 + Q CH3
X x
C1 D 1
Endo Exo

Scheme 20. ISC Control of Diastereoselectivity

H. Photoenolization of a—(2,4,6-triisopropylphenyl)acetophenone

Hart has reported that. irradiation of 1,2,2-trimesitylethenol gives 1,2,2-
trimesitylethanone, as an intermediate, en route to formation of enol ethers (Scheme

21).85 ’86 Thus a precedence for phototautomerization of enol to ketone was established.

37

O
Mes: :OH 11V Mes h Mes OMes
V __
Mes : <
Mes Mes O H Mes
+
Mes Mes

H OMes

1M3== “III;

Scheme 21. Phototautomerization of Enol to Ketone

Wagner and Meador reported that irradiation of (Jr—(2,4,6-

triisopropylphenyl)aceto- phenone results in formation of its enol and an indanol in a 10:1

and 1:1 ratios in dioxane and benzene, respectively (Scheme 21 ).36”
CH3
CH3 OH
0» .____.. ‘ o . ., «r—m \ .
V H
HO Ph

Scheme 22. Photobehavior of a-(2,4,6-triisopropylphenyl)acetophenone

An interesting question can be raised. Is the indanol formed by O-hydrogen
abstraction followed by cyclization from the ketone or as a result of a rearrangement from
the enol? The authors suggested that the enol photoreverts to ketone and acts merely as an
internal filter, lowering the quantum yield for cyclization.87 We have performed
experiments to test this hypothesis. The results of our investigation are given in this

thesis.

38

IV. Goals of Research

1) Triplet biradicals must intersystem cross to the singlet surface in order to form
products. When two biradical conformers lead to formation of different products. ISC
must play a key role in determining the product ratios. Furthermore, certain biradical
geometries have been postulated to cause more efficient ISC.75‘76 The effect of
temperature on product ratios from a-(o-alkylphenyl) and (1-(2,4,6-
trialkylphenyl)acetophenones, and propiophenones has been investigated. The results of
these studies have been rationalized in terms of population and reaction rates, which
encompass ISC rates of various biradical conformers.

2) The singlet state reactions have been postulated to occur via either a concerted
path or very short-lived biradical intermediates that do not allow equilibration (bond

. I 1.60.61.62,63
rotation).

We have studied the photobehavior of several a-(o-alkylphenyl) and
a-(2,4,6-trialkylphenyl)acetones at various temperatures to gain a better understanding of
the factors that control Singlet state and/or singlet biradical reactivity. These results in
conjunction with the results of acetophenones have been used to compare and contrast
singlet vs. triplet reactivity.

3) As mentioned earlier, four ground state parameters: (1, the distance between O
and H; T], the O-H-C angle, v, the C=O~H angle; and (1), the dihedral angle that the O-H
vector makes with respect to the nodal plane of the carbonyl have been considered to be
the most important in determining the rate and efficiency of hydrogen abstraction. To

examine the influence of these factors, in particular the dihedral angle, we have

investigated the photochemistry of o-(2’-(2’,3’-dimethy1)butyl)benzophenone. The results

39

of this investigation along with semiempirical calculations have been used to explain the

importance of dihedral angle on reactivity.

Results

1. a-Arylacetophenones and derivatives

A. General Preparation of the Ketones
a-(o-Alkylphenyl)acetophenones and or-(2,4,6-trialkylphenyl)acetophenones had
been prepared by Park88 and were used without any further purification.
or-(o-Alkylphenyl)propiophenones and a-(2,4,6-tiialkylphenyl)propiophenones were
similarly prepared from o-arylacetonitriles by a-methylation with LDA and methyl iodide
followed by coupling with phenyl Grignard or phenyl lithium reagents. As a result, the
following compounds were prepared and/or used in this study.

\
Ph

 

1 2 3
CH3 (CD3) CH3 (CD3) Ph
Ph P“ Ph
0 . 0 ° 0 .
4, 4d3 5,5d3 6
Ph
Ph Ph Ph
. 0 . o .
O \
7 8 9

40

41

B. Irradiation of Ketones

NMR scale irradiations were carried out on 0.01 M solutions of ketones in
deuterated solvents. In order to achieve n,rr* excitation, the ketones were irradiated
through Pyrex (>290 nm) or Uranium glass (>334 nm) filters. For solid state irradiations,
crytals were packed in capillary tubes and irradiated. The resulting solid (crystal) was
then dissolved in CDC13 and analyzed by NMR. The irradiation sources included a
medium pressure mercury arc lamp and a Rayonet reactor. The ketones were irradiated at
-72°, 0°, room temperature (24°) and 110°C to determine the effect of temperature on
product ratios. The desired temperatures were attained by dry ice-ethanol. ice-water,
water (at RT) and heated Silicon oil baths, respectively. Irradiation solvents included
deuterated benzene, toluene and methanol. In most cases the starting ketones disappeared
after 30-40 minutes of irradiation with the corresponding appearance, of diastereomeric
mixtures of 2-phenyl-2-indanols. In all cases material balances were > 95%. In the cases
of compounds 3, 4 and 7, type I cleavage products were also formed. Irradiation of
compound 4 at -72°C, however, did not result in type I cleavage. For compound 9, longer
wavelength irradiation (366 nm) was necessary to determine the quantum efficiency,
Since the enol product absorbs strongly between 300 and 340 nm. Chemical yields were
measured by irradiating 0.01 M solutions of ketones in benzene-d6 or toluene-d3 at room
temperature (24°C), with methyl benzoate as an internal standard. The resulting mixtures
were then analyzed by NMR or GC or both. Chemical yields at other temperatures were
calculated based on product ratios and overall chemical yield at room temperature. The

values at high temperature were checked by heating samples that had been irradiated at

42

room temperature to 110°C for three hours. Subsequent analysis gave the same product
yields as before, indicating that dehydration was not effecting the product ratios.

The structural assignments of indanols were straightforward in most cases. Methyl
doublets at 0.6-1.5 ppm were most informative because it is generally accepted that a
methyl cis to the phenyl is significantly shielded relative to one trans, as previously

. 89 .90
observed in a number of such products.

For example, in photoproducts from 0-
ethoxybenzophenone, the chemical Shift of methyl group of E isomer was Shifted much
more upfield than that of Z isomer, as Shown in Scheme 23.91

o ./

4.58 ppm

  
   

”Ill/CH3
s“ OH \
Ph 0.83 ppm
E-isomer Z-isomer

Scheme 23. Chemical Shifts of Methyls Trans and Cis to Phenyl in Five-Membered
Rings

a. a-(o-EthylphenyDacetophenone (I)

Irradiation of 1 in benzene or methanol resulted in formation of isomeric 2-

phenyl-2-indanols, previously identified by Park.”88

Preparative scale irradiation of l in
benzene followed by preparative scale TLC (PTLC) using 3% ethyl acetate in hexane as
eluent resulted in separation of the two products which were identified as two isomeric 2-

phenyl-Z-indanols (lindZ and lindE) by their NMR Spectra in CDCl3 (Scheme 24). The

signal of the trans methyl appears at 1.16 ppm, while that of the cis methyl appears at

43

0.72 ppm. It is also noteworthy that the methine hydrogen cis to the OH is more Shielded

than one cis to phenyl.

 
 

Ph ,
\W __h\_'__. H
O Toluene

/

      

H ”CH3 H3C 0H\
3.32 ppm 0.72 ppm 1.16 ppm 3.47ppm
1 "ME lindZ

Scheme 24. Photochemistry of 1

Quantitative analysis of product ratios at several temperatures was achieved by
irradiating 0.01 M solutions of l in toluene-d3 through a Pyrex filter followed by NMR
analysis. GC analysis of the mixtures showed Similar product ratios as NMR.
Quantitative results of temperature studies for compounds 1-8 are listed in Table 23.
Irradiation of crystalline 1 at 0°C resulted in formation of lindZ and lindE in a ratio

>30: 1. The chemical yields are listed in Table 3.

Table 3. Chemical Yields of Photoproducts of a-(2-Ethylphenyl)acetophenone in
Toluene at Various Temperatures (A > 290)

 

 

 

 

 

 

Temperature (0 C) lindZ lindE
-72 92.5% 3.5%

0 91% 5%

24 90% 6%

I 10 88% . 8%

 

 

 

 

44

. b. a-(2,4,6-Triethylplienyl)acetophenone (2)

Irradiation of a 0.01 M solution of 2 in benzene-d6 resulted in formation of two
isomeric 2-phenyl-2-indanols (2indZ and 2indE, Scheme 25) previously identified by
Park.“88 Preparative scale irradiation of 2 in benzene followed by PTLC, using 5% ethyl
acetate in hexane as eluent, resulted in isolation of the photoproducts, which were
identified from their corresponding NMR spectra in CDCI3. Each isomer showing a
methyl doublet, a methine quartet and an AB quartet signal with coupling constants

87.88

similar to previously identified indanols. The NMR Signal of the trans methyl appears

at 1.25 ppm while that of the cis methyl appears at 0.70 ppm.

 

Ph
hv
O Toluene

 

3.39 ppm 0.70 ppm 1.25 ppm 3-60 PDT"

2 ZindE ZindZ

Scheme 25. Photochemistry of 2

The product ratios were determined by integration of the methyl doublet signals
of each isomer and by GC analysis. Photolysis of crystalline 2 resulted in 2indZ as the

only detectable photoproduct. Chemical yields are listed in Table 4.

45

Table 4. Chemical Yields of Photoproducts of a-(Z,4,6-Triethylphenyl)acetophenone
in Toluene at Various Temperatures (1. >290)

 

 

 

 

 

 

Temperature (0 C) ZindZ ZindE
-72 97% 3%
0 96% 4%
24 95% 5%
l 10 94% 6%

 

 

 

 

c. a-(o-Tolyopropiophenone (3)

Photochemistry of 3 was previously studied by Wagner and Zhou.58 However, in
our effort to study the effect of temperature on product ratios we reinvestigated its
photochemistry. Preparative scale irradiation of 3 in methanol followed by PTLC resulted
in isolation of eight products, identified by their NMR spectra in CDCl3 as two isomeric
2-phenyl-2-indanols (3indZ and 3indE), two isomeric l-phenyl-2-tolyl-1-propanols
(photoreduction products- 3red), two isomeric diarylethanes (or-cleavage products-
3cleav), B-tolylpropiophenone and benzaldehyde. Isolation of two indanol isomers was
surprising since the previous investigators had reported the formation of only the Z-
isomer.58 The two indanols isolated had the same spectroscopic data as those isolated
from 1. The signal of the trans methyl appears at 1.16 ppm while that of the cis methyl
appears at 0.72 ppm. Table 23 contains the product ratios of irradiation of 3 at various

temperatures. Chemical yields are listed in Table 5.

46

Table 5. Chemical yields of Photoproducts of a-(o-Tolyl)propiophenone in Toluene
at Various Temperatures (1 >290)

 

 

 

 

 

 

Temperature (°C) 3indZ 3indE B—Phenylpropiophenone a-Cleavage
-72 48% 1% - l 7%
0 36% 2% 8% 3 1%
24 30% 2% 8% 35%
l 10 20% 2% 12% 44%

 

 

 

 

 

Ph
hv
0 Toluene

   

3imfl 3indE

0.95 and 1.30 ppm

     

1.0 and 1.20 ppm

3cleav-Two isomers

3red-Two isomers

Scheme 26. Photochemistry of 3

 

47

d. a—(o-Ethylphenyl)propiophenone (4, 4d,)

Irradiation of 4 at room temperature in benzene or methanol results in formation
of a mixture of products, most of which were previously identified by Park.88 Preparative
scale irradiation of 4 in methanol followed by PTLC, using 3% ethyl acetate in hexane,
resulted in isolation of these photoproducts. The products were identified (by their NMR
spectra in CDC13) as two isomeric 2-phenyl-2-indanols (4indZZ and 4indZE), two
isomeric diethylphenylbutanes (oz-cleavage products- 4c1eav), two isomeric l-pheny1-2-
(o-ethylphenyl)-1-propanols (photoreduction products- 4red) and benzaldehyde. The
symmetric ZZ-indanol had a doublet signal at 1.19 ppm corresponding to both methyls
while the ZE isomer had two distinct methyl doublet signals, the methyl trans to phenyl
appearing at 1.3 ppm, and the methyl cis to phenyl at 0.74 ppm. Furthermore, the
spectrum of the 22 isomer shows only one methine signal due to the symmetry of the
structure while that of the ZE isomer shows two distinct methine signals. Product ratios
were determined by NMR integration and GC analysis. The ratio of the two isomeric
indanols (4indZZ and 4indZE) from 4 were 5:1 and 1:1 in benzene and methanol
respectively.

It was important to know which methyl group ends up cis to phenyl in the ZE
isomer. Irradiation‘of the oc—trideuteriomethyl 4 showed that only the ethyl methyl ends
up cis to phenyl in the ZE isomer, Since the ZE-indanol had a methyl doublet Signal at
0.74 ppm but not one at 1.3 ppm (Scheme 26). The 2H NMR spectra of the 22 and the

ZE-indanols Show broad singlets at 1.29 and 1.4 ppm, respectively. These chemical shifts

48

are 0.1 ppm higher than those from the fully protonated 4. The difference could be due to

using the DMSO-dg sample rather than CDC], as the reference.

3.5 ppm 0.74 ppm
1.19 ppm 3-23 PPm \
\ \ \ \
H C

\ Ph

‘ hv
/' 0 Toluene

 

1.19 ppm 3.5 ppm 1.30 ppm 3.90 ppm
4 4rmrzz mar:
325 ppm 3.20 and 3.26 ppm

   

   

3 5 3 28 ppm
. ppm \ /0.74 ppm
OH
'V’I’Ph
C03 \
3.90
3.5 ppm 1.40 ppm PPm
1.29 ppm
mam, Mums-d.

Scheme 27. Photochemistry of 4

49

An interesting solvent effect was observed in the photolysis of compound 4.
Irradiation in toluene-d3 results in a 1:9 ZZ/ZE ratio at -72°C (Table 23). However,
irradiation at ~72°C in methanol results in formation of 4indZE as the exclusive
photoproduct. Type I cleavage products were not observed in the low temperature
irradiation mixtures. Irradiation of crystalline 4 was unsuccessfirl Since the crystals
melted during photolysis. IndanolS were the only products observed in the oil obtained
from crystal irradiations, in a 1:2 ZZ/ZE ratio. Low temperature irradiation of crystals at

0 and -72°C resulted in no reaction. Chemical yields are listed in Table 6.

Table 6. Chemical Yields of Photoproducts of a—(2-Ethylphenyl)propiophenone in
Toluene at Various Temperatures (1. >290 nm)

 

 

 

 

 

Temperature (0 C) 4indZZ 4indZE a-Cleavage
-72 9% 91% -
O 27% l 8% 47%
24 4 l % 7% 46%
iiiiiii l l 0 3 7% 4% 5 6%

 

 

 

 

 

 

e. a-(2,4,6—Triethylphenyopropiophenone (5)

Irradiation of 0.01 M solutions of 5 in benzene-d6 and methanol-d4 at room
temperature results in formation of two isomeric 2-phenyl-2-indanols (SindZE and
SindEZ, Scheme 28) previously identified by Park.88 Preparative s‘cale irradiation of 5 in

toluene followed by PTLC, using 7% ethyl acetate in hexane, results in isolation of

50

photoproducts which were identified by their corresponding NMR spectra in CDC13.

Chemical yields are listed in Table 7.

Table 7. Chemical Yields of Photoproducts of a—(2,4,6-Triethylphenyl)
propiophenone in Toluene at Various Temperatures (A > 290 nm)

 

 

 

 

 

 

Temperature (° C) SindZE 5indEZ
-72 86% l 4%
0 60% 40%
24 54% 46%
I 10 40% 60%

 

 

 

 

 

3.45 ppm 0.86 ppm

5 5mm SindEZ
Scheme 28. Photobehavior of 5
The structural assignment for the isomeric indanols 5indZE and 5indEZ was a

difficult task in the fully protonated species since both isomers had NMR signals

corresponding to methyl doublets cis and trans to the phenyl ring. (Scheme 29)

51

 

3.45 ppm

1.29 ppm

5indZE-d3 SindEZ-d3
Scheme 29

In the ZE isomer, the trans methyl signal appears at 1.47 ppm while that of the cis
methyl appears at 0.86 ppm. In the EZ isomer, the trans methyl Signal appears at 1.29
ppm while that of the cis methyl appears at 0.82 ppm. Introduction of an a—CD3 group in
place of or—CH3 made the assignments much easier, Since the ZE isomer displayed only
the methyl doublet signal cis to phenyl, while the EZ isomer had one trans to phenyl. The
2H NMR spectra of the ZE and the EZ-indanols Show singlets at 1.48 and 0.82 ppm
(CDC13 reference), respectively. Low temperature irradiation at -72°C in toluene and
methanol resulted in 6:1 and 12:1 ZE/EZ ratios, respectively. Irradiation of crystalline 5
results in formation of 5indZE as the only observable product (5% conversion).
Irradiation of crystal for 22 hours resulted in an oil, the NMR of which indicated the
presence of both indanols 5indZE and 5indEZ in a 17 to 1 ratio. Irradiation of 5 on silica
resulted in a 10:1 ZE/EZ ratio of indanols. Table 23 contains the product ratios of

irradiation of 5 at various temperatures.

52

fl a-(o-BenzylphenyDacetophenone(6)

Irradiation of 6 in benzene resulted in formation of two isomeric 2-phenyl-2-
indanols (6indZ and 6indE, Scheme 30) previously identified by Park.88 Preparative
scale irradiation in toluene followed by PTLC, using 5% ethyl acetate in hexane, resulted
in isolation of the photoproducts which were identified by their corresponding NMR
spectra. Stereochemical assignment of the two isomers was made using nuclear
Overhauser enhancement (nOe) experiments. Irradiation of the doubly benzylic methine
signal at 4.61 ppm in the E-isomer in benzene-d6 resulted in enhancement of the OH
signal at 2.45 ppm (5%), while Similar irradiation in the Z-isomer resulted in no such
enhancement. The signal at 2.45 ppm disappeared upon addition of two drops of D20 to
the solution. The product ratios were determined by NMR and GC analysis. For the NMR
analysis, the ratio of the AB quartet signals of the Z-isomer, which appears at 3.4 and
3.65 ppm, to that of the E-isomer, which appears at 3.3 and 3.85 ppm, was used. Table 8
contains the product ratios of irradiation of 6 at various temperatures. Irradiation of 6 in
methanol resulted in a 1:1 ratio of indanols. Irradiation of cystalline 6 also results in a 1:1

Z/E indanol ratio. Chemical yields are listed in Table 8.

Ph

Ph
0 Toluene

   

Scheme 30. Photobehavior of 6

53

Table 8. Chemical Yields of Photoproducts of a-(Z-Benzylphenyl)acetophenone in
Toluene at Various Temperatures (1. > 290 nm)

 

 

 

 

 

 

Temperature (° C) 6indZ 6indE
-72 41% 59%
O 50% 50%
24 55% 45%
I 10 60% 40%

 

 

 

 

g. a-(o-Benzylph enprropiophenone (7)

Irradiation of a 0.01 M solution of 7 at room temperature in benzene-d6 resulted in
formation of a mixture of products. Preparative scale irradiation in toluene followed by
PTLC, using 3% ethyl acetate in hexane, resulted in isolation of photoproducts which
were identified by their NMR spectra (in CDC13) as two isomeric 2-phenyl-2-indanols
(7indZZ and 7indZE), two isomeric di(benzylphenyl)butanes (OI-cleavage products-
7cleav) and benzaldehyde (Scheme 31). Although the chemical shift of the methyl
doublet Signals from both indanols indicated a trans configuration relative to the 2-
phenyl, the stereochemical orientation of the 3-phenyl groups in the two isomers was
ambiguous. NOe experiments were performed. Irradiation of the benzylic methine signal
of one isomer at 4.50 ppm resulted in a small enhancement (0.47%) of the methyl doublet
at 1.30 ppm. However, irradiation of the benzylic methine signal of the other isomer at

4.95 ppm did not result in signal enhancement of the methyl doublet at 1.25 ppm. Thus,

54

the former was assigned as the 213 while the latter was assigned as the Z2 isomer.
Irradiation of 7 at -72°C resulted in formation of both type I and type 11 products. Two
indanols were formed in a 1:1 ratio at all temperatures studied. The chemical yields were
measured by NMR analysis and were 55% and 35% for indanols and d-cleavage products

at room temperature, respectively.

 

Ph
Ph
hv
O Toluene
7 4.5 ppm
7indZE
320 ppm 1.10 ppm

   

1.10 ppm

7cleav-Two isomers

Scheme 31. Photobehavior of 7

h. a-Mesitylpropiophenone (8)

The photochemistry of compound 8 was previously studied by Wagner and
Zhou,58 but temperature effects on the diastereoselectivity of the biradical closure were

not studied. Irradiation of 8 in benzene results in formation of two isomeric 2-phenyl-2-

55

indanols (8indZ and 8indE, Scheme 32). Preparative scale irradiation followed by PTLC.
using 3% ethyl acetate in hexane, resulted in isolation of photoproducts which were
identified by their NMR spectra in CDCl;,. Analysis of product ratios by NMR was
simple since the methyl doublet signal from the Z-isomer appeared at 1.36 ppm while that
for the E-isomer appeared at 0.7 ppm. The product ratios were determined by both NMR
and GC analysis. Table 23 contains the product ratios at various temperatures. Chemical

yields are listed in Table 9.

Table 9. Chemical Yields of Photoproducts of a—Mesitylpropiophenone in Toluene
at Various Temperatures (1» > 290 nm)

 

 

 

 

 

 

Temperature (0 C) 8indZ 8indE
-72 96% 4%
0 94% 6%
24 9 1 % 9%
I 10 82% l 8%

 

 

 

 

Ph
hv
O Toluene

 

Scheme 32. Photochemistry of 8

56

i. a-(2,4,6-Triilsopropylphenyl)acetophenone (9)

The photochemistry of 9 (Scheme 33) was previously studied by Wagner, Meador
and Zhou.87 Here, a systematic study of product ratios as a function of temperature and
conversion is presented. Irradiation of 9 at -72 °C in both methanol and toluene forms
only enols (9ean and 9enlE), together with 5-10% benzaldehyde. Only Z-enol was
observed in toluene at low temperature, while a 4:1 Z/E enol ratio was observed in
methanol. The Z-enol was identified by the following NMR signals in toluene: a vinylic
CH signal at 6.1 ppm, an OH signal at 4.8 ppm and methyl doublet signals at l.2-1.30
ppm. The E—enol has a vinylic CH signal at 6.4 ppm, an OH signal at 4.75 ppm and
methyl doublet Signals at 1.1-l.2 ppm (in toluene-d3). The vinylic CH signal of the Z-
isomer is further upfield than that of the E-isomer presumably due to partial shielding by
the phenyl group. The enols are stable for days at room temperature in the dark, but
tautomerize completely to ketone within 5 hours at 90 °C. Upon irradiation at 313 nm at
room temperature they revert to 9, whereas the Z-trimethylsilyl enol ether of 9,
synthesized by treating 9 with KH and trimethylsilylchloride, affords only the E-isomer.
The Z:E enol ratio in toluene decreases as irradiation time increases, ranging from 10:] to
2:1. A study of product yields as a function of conversion, temperature, and excitation
wavelength (Table 12) indicated that indanol (9ind) builds up very slowly following
several interconversions between ketone and enol at 313 nm excitation but is obtained in
a constant quantum yield at 366 nm (Table 11), where the enol does not absorb (Table
10). Irradiation of 9 at 366 nm thus results in a constant 8:1 enol/indanol ratio. Irradiation

of crystals of 8 produces only Z-enol up to 20% conversion.

57

Table 10. Molar Absorptivity Coefficients (M'lcm'l) of 9 and its Enol at Various
Wavelengths

 

 

 

 

 

Compound 83,3 833,, 8366

9 79 70 = 6.2
Enol of 9 1230 22 0
Z-Trimethylsilylenol ether of 9 1912 98 0

 

 

 

 

 

6.40 m
ppl 4.75 ppm
\ Ph H \
hv OH
0 Toluene , ——
/ "’1 + 0 Ph

1.29 ppm (in CDCl 3)

 

0.78 ppm (in CDCI 3)
9 9ind 9enlE

1.95 ppm (in CDCI 3)
6 1 P131“ 4 79 ppm (in CDCl 3)

/

H3C
H H/ 110;me
—_:\75+ ppm

9ean 9alc

Scheme 33. Photobehavior of 9

Table 11. Product Quantum Yields

58

of 9 as a Function of Conversion and

 

 

 

 

 

 

 

 

 

Wavelength
1. (nm) °/oConversion [Enol] (Dem, ' [Indanol] (bindmo, "b
3 I 3 6 0.0065 0.35 - -
313 15 0.013 0.234 0.003 0.062
313 19 0.014 0.15 0.006 0.059
313 24 0.014 0.09 0.009 0.052
366 10 0.13 0.64 - -
366 18 0.18 0.64 0.024 0.085
366 25 0.24 0.64 0.034 0.085

 

 

 

 

 

 

a) Quantum yields were measured by NMR (b) Quantum yields were measured by GC

[Ketone]= 0.0143 M (GC studies), [Ketone]= 0.0983 M (NMR studies)

[Valerophenone]= 0.024 M (GC studies), [Valerophenone]= 0.1165 M (NMR studies)

[C20 standard]= 0.0033 M (GC studies), [Methyl benzoate-standard]= 0.03 M (NMR

Studies)

 

59

Table 12. Product Ratios of Irradiation of 9 Under Various Conditions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T (° C) 1. (nm) Solvent % Conv. 9ind 9(2an 9enlE Cleavage
-72 >290 Toluene >95 0 90 0 1 0
-72 >290 Methanol >95 0 72 1 8 10
24 >290 Benzene 40 20 73 7 0
24 >290 Benzene 50 28 62 7 3
24 >290 Benzene 64 30 53 7 1 0
24 >290 Benzene 70 50 16 8 26
24 >334 Benzene 17 29 71 - -
24 >3 34 Benzene 3 23 24 63 1 3 -
24 >3 34 Benzene . 46 26 59 15 -
24 >3 34 Benzene 66 20 53 24 23
24 >334 Benzene >95 55 0 0 45
90 >290 Toluene 24 1 7 66 1 7 0
90 >290 Toluene 38 3 5 52 l 3 0
90 >290 Toluene 70 69 25 6 0
90 >290 Toluene >95 1 00 0 0 0

 

 

 

 

 

 

 

 

 

60

C. Steady-State Photokinetics.

The quantum yields were measured by irradiation of degassed solutions of ketones
(0.025-0.04 M) in tubes containing a fixed amount of internal Standard parallel to
valerophenone actinometer. For quenching studies, these tubes also contained varying
amounts of 2,5-dimethyl-2,4-hexadiene quencher. Product yields at 5-18% were measured
using CC or NMR and were converted to quantum yields. Stern-Volmer plots were linear
with slopes equal to qu. The kinetic data are listed in Table 13 and Table 14. Triplet
lifetimes, based on a kq value of 6x109 M'ls'l, are also listed.30 The errors represent deviation

of 2-4 measured values from the average.

Table 13. Lifetimes of Triplet Aceto- and Propiophenones in Benzene

 

 

 

 

 

 

 

Ketones kqt’ M" “1, 1098-1
1 8.04 i 0.4 0'75
""""" 2 6.95 i 0.3 0'86
"""""" 4 17.40 i 0.8 0'34
............. 5 7.98 i 0.4 0.75
............. 6 3.99 i 0.2 1.5

 

 

 

 

61

Table 14. Quantum Yields of Photoproducts from Aceto- and Propiophenones in
Benzene

 

 

 

 

 

 

 

 

 

Ketones (Dcyc (DCleavage
1 0.48 i 0.02 -
2 0.48 i 0.02 -
4 0.064 i 0.004 0.43 i”. 0.02
5 0.27 i 0.015 -
6 0.40 i 0.011 -
7 0.10 i’ 0.005 0.06 i 0.005
9 0.055, 0.0853 i 0.003 -

 

 

 

 

a) Quantum Yield measured at 366 nm.

62

II. a-Arylacetones

A. General Preparation of the Ketones.

a-Arylacetones were prepared by chloromethylation of the appropriate arylbenzene,
cyanation with sodium cyanide, hydrolysis with concentrated hydrochloric acid, and coupling
with methyllithium. AS a result, the following compounds were prepared and/or used in this

Study.

B. Irradiation of Ketones

NMR scale irradiations were carried out using 0.01 M solutions of ketones in
deuterated benzene and toluene. The solutions were irradiated through a Pyrex filter
(>290 nm). The ketones were irradiated at -72°, 24° and 110°C to determine the effect of
temperature on product ratios. In most cases, the starting ketones disappeared after 24

hOurs of irradiation with corresponding appearance of mixtures of 2-methyl-2-indanols

63

and (Jr-cleavage products. In the case of compounds 10 and 12, two isomeric indanols
were detected after irradiation. The isomeric ratios of these indanols were determined by
GC and/or NMR. Chemical yields were measured by irradiating 0.01 M solutions of
ketones in benzene-d6 at room temperature (24°C) using methyl benzoate as an internal
standard. The resulting mixtures were then analyzed by NMR or GC or both. Chemical
yields at other temperatures were calculated based on product ratios and overall chemical
yield at room temperature. The values at high temperature were checked by heating the
solution, which had been irradiated at room temperature, to 110°C for three hours
followed by analysis to ensure that dehydration of indanols was not affecting the product
ratios. In most cases material balances were > 95%. Stem-Volmer quenching experiments
using 2,5-dimethyl-2,4-hexadiene as quencher, Show a quenchable a-cleavage reaction
while no quenching of indanol formation was observed. Our experiments thus indicate
that 8—hydrogen abstraction occurs from the singlet while a-cleavage occurs from the

triplet in a-alkylphenylacetones, in agreement with Turro’s67 results.

C. Identification of Photoproducts

a. a-fl-Ethylphenybacetone (10)

The behavior of 10 is temperature and environment dependent. Irradiation of 10 in
benzene resulted in formation of a mixture of compounds. Preparative scale irradiation
followed by PTLC, using 3% ethyl acetate in hexane, resulted in separation of
Photoproducts which were identified as two isomeric 2-methyl-2-indanols (10indZ and

lOindE, Scheme 34) and 1,2-di-(o-ethylphenyl) ethane (or-cleavage product- l0cleav).

64

Analysis of product ratios in benzene by NMR was not easy due to overlapping peaks,
thus irradiations were performed in toluene which gave much better peak separations. The
structural assignment for the isomeric indanols 10indZ and 10indE proved to be a
difficult task since all methyl Signals appeared in close proximity to each other in the
NMR Spectrum. The NMR spectra of the cis and trans l-methyl-2-indanols were
previously reported in literature92 , however, the presence of the methyl group at the 2-
position Should change the chemical Shifts, so comparisons are not reliable. The structural
assignments of the indanols were based on the use of shift reagents and nOe experiments.
Addition of Rondeau’s reagent, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethy1-3,5-
octanedionato) praseodymium, to 0.01 M solutions of each indanol in CDC13 caused an
upfield shift of all proton signals. The methine Signal at 3.08 ppm of the minor isomer
moved upfield (to 2.97 ppm) twice as much as its methyl signal at (1.19 ppm to 1.16
ppm), while the upfield shift of both methyl (1.28 to 1.0 ppm) and methine (2.97 to 2.68
ppm) signals of the major isomer were comparable. Addition of europium shift reagent
caused a similar downfield shifi of the signals but caused peak broadening which made
assignments difficult. Furthermore, irradiation of the methine signal in the minor isomer
caused an nOe enhancement of the OH signal. These data strongly suggest that the minor
isomer has E-stereochemistry. The product ratios and indanol diastereoselectivities were
measured by NMR analysis. The Z:E indanol ratio was determined by the ratio of the
methyl doublet signal of the Z-isomer at 1.12 ppm to that of the E-isomer at 1.0 ppm in
toluene-d8. Irradiation of 10 resulted in 20:80, 50:50 and 60:40 indanol/diarylethane

ratios at -72°C, 24°C and 90°C, respectively. Furthermore, the ratio of the two isomeric

 

65

indanols (10indZ: 10indE) were 3.2:1, 2.521 and 1.421 at 0°C, 24 °C and 90 °C .
respectively. Irradiation of 10 inside sodium dodecylsulfate micelles (0.4 g in 100 m1 of
water, 14 mM, critical micellar concentration (CMC) = 10 mM)93 at 24°C resulted in a

75:25 indanol/ci—cleavage ratio, while the lOindE: 10indZ ratio remained 2.5:]. Chemical

yields are listed in Table 15.

Table 15. Chemical Yields of Photoproducts from a-(2-Ethylphenyl)acetone in
Toluene at Various Temperatures (1. > 290 nm)

 

 

 

 

 

 

Temperature (° C) 10indZ lOindE l0cleav
-72 20%” -3 80%
0 34% 1 1% T 47%
24 33% 13% 48%
1 10 28% 28% i 39%

 

 

 

 

 

a. Only the Z-indanol was observed in the product mixture irradiated at -72°C, the E-
isomer might have been present in trace amounts but could not be detected by NMR.

   

C I \ / H CH3
1-23 131"“ 2.97 ppm 3‘08 ppm
10 101ng 10MB 10cleav

Scheme 34. Photoproducts of 10

66

b. a-Mesitylacetone (11)

Irradiation of compound 11 (Scheme 35) in toluene-d8 resulted in formation of
two products which were identified as an indanol (llind) and a diarylethane (1 lcleav) by
their NMR Spectra. Preparative scale irradiation in toluene followed by PTLC, using 3%
ethylacetate in hexane, resulted in separation of photoproducts. The product ratios were
determined by comparing the NMR integration of the AB quartet signal of the indanol at
3.0 ppm to that of the methylene Signal of the diarylethane at 2.8 ppm. Irradiation of 11 at
-72 °C, 24°C and 110°C resulted in a 0:100, 60:40, and 70:30 indanol/diarylethane ratio,
respectively. No reaction takes place upon irradiation of crystals. Chemical yields are

listed in Table 16.

 

1.30 ppm (in CDC13) 2-80 ppm (in CDCI 3)

1‘ llind llcleav

Scheme 35. Photochemistry of 11

67

Table 16. Chemical Yields of Photoproducts from a-Mesitylacetone in Toluene at
Various Temperatures (1. > 290 nm)

 

 

 

 

 

Temperature (0 C) llind llcleav
-72 0 i 98%
24 56% 42%
l 10 69% 29%

 

 

 

 

c. a-(2,4,6-Triethylphenybacetone (12)

Irradiation of compound 12 in benzene-d6 or toluene-d3 resulted in formation of a
mixture of two isomeric indanols(12indZ and 12indE) and a-cleavage products, 12cleav
and acetaldehyde (Scheme 36). Preparative scale irradiation in benzene followed by
PTLC, using 5% ethyl acetate in hexane, resulted in separation of the indanols as a
mixture from the diarylethane. The indanol/diarylethane ratios were measured by NMR
analysis to be 20:80, 70:30, and 85:15 at -72°C, 24°C, and 110°C, respectively. They
were determined from the ratio of the methyl signal of the Z-indanol at 1.26 ppm to that
of the methylene of the diarylethane at 2.5 ppm. The ratio of the two isomeric indanols,
measured by NMR and GC, was 10:1 in favor of the Z-isomer for irradiations at 24°C in
benzene. The indanol ratios were determined by NMR integration of the methyl doublet
signal of the Z-indanol at 1.19 ppm to that of the E-indanol at 1.11 ppm in C6D6. The
peaks for the two isomeric indanols overlap and separation is difficult. The Z-
Stereochemistry for the major indanol was based on the comparison of the peaks to that of

the Z-indanol of o-(ethylphenyl)acetone. Chemical yields are listed in Table 17 .

 

68

Table 17. Product Chemical Yields of a-(2,4,6-Triethylphenyl)acetone in Toluene at
Various Temperatures (1. >290 nm)

 

 

 

 

Temperature (°C) 12indZ 12indE 12cleav
-72 l 7% ~2%a 7 l %
24 5 8% 6% 27%
1 l 0 71 % ~6%a l 2%

 

 

 

 

 

a) The yield of the 12indE was estimated based on the 12indZ yield and a constant 10:1

indanol ratio, since ratios at other temperatures were hard to determine due to overlapping

   

peaks.
\ l-
\
i / 0 H H
/ 2.50 ppm
1.19 m 1.11 m
99 2.72 ppm 99 2.56 ppm
12 IZInfl 121:1 dE 12cleav

Scheme 36. Photobehavior of 12

d. a-(2,4,6-Triisopropylphenyl)acetone (13)

The photobehavior of 13 (Scheme 37) at room temperature is conversion
dependent. At low conversions the Z-enol (Ben!) is the major photoproduct. It was
identified by the following NMR signals in benzene: an allylic methyl at 1.8 ppm, a
vinylic CH at 5.4 ppm and a OH at 4.4 ppm. The Z-stereochemistry was assigned based

on its stability relative to the E-isomer and by comparison of its NMR data to the

69

literature values (Z-enol of phenylacetone is reported to have a vinylic CH signal at 5.0
ppm in benzene).94 At high conversions an indanol (13ind) and a diarylethane (13cleav)
are the only observable photoproducts. The indanol is identified by the following NMR
signals in benzene-d6: three methyl singlet signals at 1.10 at 1.30 and 1.36 ppm, an OH
Signal at 1.8 and an AB quartet signal at 2.95 at 2.99 ppm (in CDC13). Formation of the
enol is interesting since it mimics the behavior of the acetophenone analog. The enol of
13, however, is not as Stable as acetophenone enols and tautomerizes back to ketone in a
few hours in the dark at 24°C, and in a few minutes at 110°C. The behavior of 13, like its
analogs, is also temperature dependent. At -72°C, only cleavage products are formed
while at 110°C indanol is the only photoproduct. At room temperature Z-enol, indanol
and cleavage products are formed but no reaction takes place upon irradiation of crystals.
Table 18 lists product chemical yields as a function of conversion and temperature. The
product ratios are determined by NMR integration of the vinylic CH signal of the enol,

the methyl singlet signal of the indanol and the methylene singlet signal of the

        

 

diarylethane.
5.2 ppm
1.36 ppm(CDCl 3) /
l hv
/ O “'CH
.\ C 6D 6 3 + H H
H30 CH3 ‘
\ l
1.10 and 1.30 ppm(CDC13)
2.90 ppm(CDCI 3)
l3 131m! 1301! 13cleav

Scheme 37. Photochemistry of 13

70

Table 18. Product Chemical Yields of a-(2,4,6-Triisopropylpheny1)acetone as a
Function of Conversion and Temperature

 

 

 

 

 

 

 

 

 

Temperature(°C) Solvent %Conversion 13¢:an 13ind 13cleav
-72 Toluene >95 0 0 100
24 Benzene 36 46 40 14
24 Benzene 55 33 45 22
24 Benzene 74 23 47 30
24 Benzene 80 1 7 48 3 5
l 10 Toluene >95 0 100 0

 

 

 

 

 

 

D. Steady-State Photokinetics.

The quantum yields were measured by irradiation of degassed solutions of ketones

(0.02-0.03 M) in tubes containing a fixed amount of internal standard parallel to a

valerophenone actinometer. For quenching Studies, these tubes also contained varying

amounts of 2,5-dimethyl-2,4-hexadiene quencher. Product yields at 5-18% were measured
using GC or NMR and were converted to quantum yields. Stern-Volmer plots were linear
with Slopes equal to kq‘t. The kinetic data are listed in Table 19 and Table 20. Triplet

lifetimes, based on a kq value of 6x109 M'ls'l, are also listed.30 The errors represent deviation

of 2-4 measured values from the average.

 

71

Table 19. Triplet Lifetimes of a-Arylacetones in Benzene at Room Temperature
(1.= 313 nm)

 

 

 

 

 

Ketones k4, M'l UT 11 109 s'1
10 ' 6.7 i 0.3 0.89
11 31.4i1.5 0.31
' 13 107.1 i 5 0.009

 

 

 

Table 20. Quantum Yields of Photoproducts of a-Arylacetones in Benzene at Room
Temperature (A=313 nm)

 

 

 

 

 

 

Ketones (DC,c (Dwarykmm
10 0.0128 i 0.0005 0.0156 i 0.0005
11 0.085 i 0.003 0.054 i 0.002
12 0.036 i 0.003 0.018 t 0.002
13 0.012 ((DEno, = 0.028) 0.005 i 0.0002

 

 

 

 

 

72

III. 2-tert-Butyl trifloroacetophenone

A. Preparation

2-tert-Butyl trifloroacetophenone (14) was prepared by nitration of the tert-
butylbenzene followed by bromination, reduction of nitro group, formation and reduction of

diazonium salt, formation of Grignard and reaction with ethyl triflouroacetate.

“j: HNo3 2
-, V/ 11.50 H2304
Ag2504

B. Irradiation Conditions

1. BuLi
2. CF3COOEt

 

   

NMR scale irradiations were carried out using 0.01 M solutions of 14 in
deuterated benzene, methanol or toluene. The solutions were irradiated through a Pyrex
filter. The starting ketone disappeared after 2 hours of irradiation with corresponding
appearance of mixtures of 3,3-dimethyl-1-triflouromethyl-1-indanol (14ind)and 1-{2’-(3-
(2”—methyl)propargyl)-phenyl}triflouromethylethanol (l4alc). Material balance was

> 95%.

C. Identification of Photoproducts

Large scale irradiation was performed in benzene. The products were isolated by

PTLC using 30% ethyl acetate in hexane solution as eluent. The products are an

73

unsaturated alcohol and an indanol and are formed in a 10:1 ratio (Scheme 38). The
unsaturated alcohol was the predominant photoproduct in both methanol and hydrocarbon
solvents (benzene). The unsaturated alcohol is identified by the following NMR signals:
an allylic methyl Signal at 1.8 ppm, an OH Signal at 2.4 ppm (d, J=4.8 Hz), an AB quartet
signal at 3.4 ppm, two vinylic CH signals at 4.5 and 4.8 ppm and a methine (dq, J=4.8,
6.8 Hz) signal at 5.3 ppm (in CDC13). Furthermore, l9F NMR of the alcohol showed a
doublet (J=6.8 Hz) signal at -2.0 ppm relative to ethyl trifluoroacetate standard. The
indanol had two methyl singlet Signals at 1.37 and 1.42 ppm and an AB quartet at 2.2 and
2.45 ppm (in CDC13). A weak w-type coupling was observed in the indanol between the
CF, group and the trans hydrogen on the five-membered ring (2.2 ppm). Chemical yields
were measured by irradiating 0.01 M solutions of 14 in benzene-d6 at room temperature
in the presence of a methyl benzoate standard. NMR analysis of the resulting mixture

showed it to consist of 88% Male, and 9% Mind.

 

4.88 ppm
1.8 ppm 4.5 ppm
2.20 ppm \ 5-3 1’1""
0 H
H
H
CF3 hV
CF3
OH \
I 2.8 ppm
2.42 ppm
14 Mind 14alc

Scheme 38. Photobehavior of 14

74

IV. 2'-(2,3-Dimethyl-2-butyl)benzophenone

A. General Preparation

0-(2,3-Dimethyl-2-butyl)benzophenone was prepared by addition of isopropyl
Grignard to acetone, treatment of the resulting alcohol with concentrated HCl, Friedel-Crafts
alkylation of benzene with the resulting alkyl chloride, nitration, bromination, reduction of
nitro group, formation and reduction of diazonium salt, formation of Grignard and coupling

to benzoyl chloride.

 

 

 

>‘Br 1 Mg L7<_fl:_l_’ HC6H6
2. (CI-I co /'
3h FeCl3 OW H2504

Br H2
HCl PtO
2.PhCOCl 2. “31,02 2
NHZ

B. Irradiation Conditions

Brz
H2304
A82504

 

 

NMR scale irradiations were carried out using 0.01 M solutions of 2'-(2,3-

dimethyl—2-butyl)benzophenone in deuterated benzene, methanol and toluene. The

75

solutions were irradiated through a Pyrex filter. In most cases the starting ketone
disappeared after 30 minutes of irradiation with corresponding appearance of mixtures of
isomeric indanols (lSindmZ, lSinde, lSindip, lSalc). The quantum efficiencies were
higher in methanol than in benzene. Chemical yields were measured by irradiating 0.03
M solutions of 15 in benzene and methanol with methyl benzoate as a standard. The
resulting solutions were then analyzed by NMR. In all cases, material balances were

>95%.

C. Identification of photoproducts.

The indanol products were difficult to isolate because of rapid dehydration on
silica gel. An unsaturated alcohol similar to those obtained from irradiation of o-tert-
butylaceto- and trifloroacetophenones was also observed as a photoproduct.

o-(2,3-Dimethyl-2-butyl)benzophenone (0.011 M) in deuterated benzene was
irradiated with Pyrex-filtered light from a medium pressure mercury arc lamp. The
reaction was complete within 1.5 hours of irradiation and four products formed (Scheme
39). The reaction mixture had to be analyzed immediately after irradiation because
photoproducts dehydrated rapidly. 15inde, lSindmZ and lSalc (Scheme 39) measure
abstraction of a primary methyl hydrogen while 15indip measures abstraction of a tertiary
hydrogen. This reaction was repeated in several solvents and product ratios were
determined by NMR. The stereochemical assignments of lSinde and lSindmZ were
made by comparison of the NMR data to those of E- and Z-3-ethyl-3-methyl-1-phenyl-l -

indanol (tamlE and tale), photoproducts of OTAMBP.” The NMR data of tamlE

76

and tale in benzene indicate that the methyl group of the ethyl substituent appears at
0.6 ppm in the E-isomer with a methyl singlet signal at 0.90 ppm which are, respectively,

upfield and downfield relative to the signals in the Z-isomer (0.5 and 1.10 ppm

 

    

    

respectively).
0.62 ppm 0.78 ppm
CH3 \
CH3 0.85 ppm
0 ..~\‘CH3 \\
\ hV . ..~“ CH3
C D
| Ph 6 6 1.40 ppm +
/ "9,! 3'”
HO P“ HO Ph
15
15mm lSinde
1.10, 1.16, 1.18, 1.45 ppm 3.26 ppm (collapsed AB quartet)
OH
+ Ph
/ \
0.92 and 0.95 ppm 5.92 ppm
lSindip ‘50“,

Scheme 39. Photochemistry of 15

0'5 ppm ”0 PM“ 0.9 ppm 0.6 ppm

 

77

Thus, the isomer with the isopropyl doublet signals at higher field and the methyl
singlet signal at lower field was assigned the E-stereochemistry. lSindmZ has two
isopropyl doublet signals at 0.62 at 0.78 ppm and a methyl singlet signal at 1.40ppm
while the isopropyl and methyl signals of lSinde appear at 0.76, 0.85 and 1.10 ppm,
respectively. Identification of 15alc by NMR was also simple, since lSalc shows similar
NMR signals to the unsaturated alcohol of 14 with two vinylic CH signals appearing at
4.47 and 4.84 ppm, a bibenzylic OH signal at 5.92 ppm, an AB quartet signal at 3.26 ppm
and two isopropyl doublet signals at 0.92 and 0.95 ppm. The reaction proceeds in solid as
well as solution similar to tert-amylbenzophenone Table 21 shows the chemical yield in
benzene and methanol at room temperature along with product ratios under various

conditions.

Table 21. Effect of Temperature and Medium on Product Ratios of 15

 

 

 

 

 

 

 

Reaction T (°C) 15indmZ 15inde 15alc lSindip
medium
Benzene 24 27 52 7 l4
Methanol 24 32 32 l 3 23
Toluene 1 10 22 29 8 41
Toluene -72 3 3 48 5 1 4
solid 24 23 27 - 50

 

 

 

 

 

 

 

78

D. Steady-State Photokinectics

The quantum yields were measured by irradiation of degassed solutions of ketones
(0.15 M) in tubes containing a fixed amount of internal standard parallel to valerophenone
actinometer. For quenching studies, these tubes also contained varying amounts of 2,5-
dimethyl-2,4-hexadiene as a quencher. Product yields at 5-18% were measured using GC or
NMR and were converted to quantum yields. Stem-Volmer plots were linear with slopes
equal to kq'c. The kinetic data are listed in Table 22. Triplet lifetimes, based on a 1(q value of

6x109 M'ls'l, are also listed.30 The errors represent deviations from the average.

Table 22. Triplet Lifetimes and Product Quantum Yields of 2-(2'-(2',3'-
Dimethyl)butyl)—benzophenone at Room Temperature (k= 313 nm)

 

 

 

 

501%!“ ME MI “T X 109 S" (DlSindlnl-Z <Disindmz (DMalc (Dmndip

Benzene 20.8 i“ 0.9 0.29 0.052 i 0.026 i 0.0060 i 0.010 i
0.003 0.001 0.0003 0.005

Methanol - - 0.130 i 0.120 i 0.061 i 0.110 i
0.007 0.006 0.003 0.005

 

 

 

 

 

 

 

 

79

V. Semiempirical Calculations

In order to gain a better understanding of our experimental results, we performed
calculations on the ground state as well as triplet biradical geometries of all of our
compounds. The results of our triplet biradical calculations are presented and discussed in
the discussion part of this thesis. The results of our ground state calculations are
presented below:

Global minimizations (semiempirical- AMI level) with dihedral drivers around
phenyl-a-carbon and a-carbon-carbonyl bonds have shown that the lowest energy
geometry of 1 does not have the phenyl group eclipsing the carbonyl (Figure 7).
However, geometry (1B) exists as a local minimum 0.8 kcal/mole higher than global
minimum. In geometries 1B (d=2.32 A, w=48°) and 1C (d=2.77 A, (0:620) but not in IA,
hydrogens are close enough for abstraction. MMX minimizations had shown 1C to be the
lowest energy geometry.87 The reason for the discrepancy between molecular mechanics
and semiempirical results is attributed to the inability of molecular mechanics to account

for electronic interactions such as torsional interactions and resonance.

 

1A. Lowest Energy Geometry of 1 IE. 0.5 kcal/mole less stable than 1A

80

 

1C. 0.8 kcal/mole less stable than 1A
Figure 7. Minimum Energy Geometries of a-(2-Ethylphenyl)acetophenone

Similar minimizations (AMI) reveal that 2 has two energy minima within 0.7
kcal/mole of each other (Figure 8). In both 2A (d=2.72 A, m=110°) and 2B (two
hydrogens are available for abstraction, one pointing up one down, dup=2.42 A, coup=67°,

ddown=2.7 l A, mdown=96°) hydrogens are close enough for abstraction.

 

2A. Lowest Energy Geometry of 2 2B. 0.7 kcal/mole less stable than 2A
Figure 8. Minimum Energy Geometries of a-(2,4,6-Triethylphenyl)acetophenone

The lowest energy geometry of 4 is calculated to be the one in which the methyl
eclipses the carbonyl (Figure 9). In this geometry, however, the methylene hydrogens are

too far to be abstracted since the carbonyl is twisted away from them. Global

81

minimizations with dihedral drivers (10° increments) around the benzene-a-carbon bond
reveal two other minima; in both, methylene hydrogens are close enough to be abstracted.
These conformers are 1.4 and 2.4 kcal/mole higher in energy than the global minimum. In
the lower energy conformer (d=3.0 A, w=86.8°), ethyl derived methyl is pointing down
and the a-phenyl is eclipsing the carbonyl, while in the higher energy conformer (d1=2.5

A, col=61.5°, d2=2.7 A, wz=99.45°), ethyl derived methyl is relatively coplanar with the 0.-

phenyl and a-methyl eclipsing the carbonyl.(Figure 9)

 

4C. 2.4 kcal/mole less stable than 4A

Figure 9. Lowest Energy Conformers of a-(Z-Ethylphenyl)propiophenone

82

The lowest energy geometry of 5 is has the a-methyl eclipsing the carbonyl
(AMI). In this geometry, the closest methylene hydrogen is 2.2 A away and makes a
dihedral angle of 50° with the carbonyl 0 plane. Another geometry, SB, which lies 1.8
kcal/mole above the global minimum with the phenyl and methyl gauche to each other. In
this geometry the closest hydrogen is 2.8 A from the carbonyl oxygen and makes a

dihedral angle of 103° with the carbonyl nodal plane.(Figure 10)

 

5A 5B. 1.8 kcal/mole less stbale than 5A
Figure 10. Lowest Energy Geometries of a-(2,4,6-Triethylphenyl)propiophenone

Semiempirical calculations show that in the lowest energy geometry of 6 the a-
hydrogen eclipses the carbonyl (6A, Figure 11). In this geometry, the benzylic hydrogens
are too far away for abstraction. In another geometry (6B) both benzylic hydrogens are

close enough for abstraction (dup=2.46 A, mup=l61.8°, ddown=2.68 A, mdown=142.2°).

83

   

6A. Lowest Energy Geometry of 6 68. 0.4 kcal/mole less stable than 6A
Figure 11. Minimum Geometries of a-(2~Benzylphenyl)acetophenone

Global minimizations reveal that in the lowest energy geometry of 7 (7A, Figure
12) benzylic hydrogens are too distant for abstraction (d= 4.8 A). Another minimum
(7B,d=2.32 A, m=48°) higher in energy than 7A by' 2.0 kcal/mole, has hydrogens close

enough for abstraction.

 

7A. Lowest Energy Geometry of 7 7B. 2.0 kcal/mole less stable than 7A

Figure 12. Lowest Energy Conformers of a-(2-Benzylphenyl)propiophenone

84

The minimum energy geometry of 8 has an cat-methyl group eclipsing the carbonyl
(AMI, 8A, Figure 13). In this geometry, two hydrogens on the same methyl group are
close enough for abstraction (dup=2,45 A, mup=122.7°, ddown=2.67 A, wdown=84.4°). There
is another geometry (8B) 2.1 kcal/mole higher in energy than 8a in which methyl and
phenyl are gauche to each other. In this geometry closest hydrogen is 2.7 A from carbonyl

oxygen and makes a dihedral angle of 105° with the nodal plane of carbonyl.

 

8A. Lowest Energy Geometry of 8 88. 2.1 kcal/mole less stable than 8A

Figure 13. Lowest Energy Geometries of a-Mesitylpropiophenone

The lowest energy geometry of 9 has the a-phenyl eclipsing the carbonyl. In this
geometry, the benzylic hydrogen closest to the carbonyl is 2.85 A from oxygen. (Figure

14)

85

 

Figure 14. Lowest Energy Geometry of a-(2,4,6-Triisopropylphenyl)acetophenone

Molecular mechanics and semiempirical calculations were performed on 10. In its
lowest energy geometry (10A) , no hydrogens are close enough for abstraction. Global
minimizations with dihedral drivers (10° increments) around benzene-a-carbon and or-
carbon-carbonyl bonds reveal another minimum (10B, 0.6 kcal/mole higher than global

minimum) in which methylene hydrogens are close enough to be abstracted (d=2.64 A,

to: 63°, Figure 15)

 

10A. Lowest Energy Geometry of 10 10B. 0.6 kcal/mole less stable than 10A

Figure 15. Lowest Energy Geometries of a-(2-Ethylphenyl)acetone

86

Global minimizations show that hydrogen abstraction in 11 must occur from a

geometry (11B, d=2.9 A, w=58°) other than its global minimum (11A, d=3.26 A), since

no hydrogens are close enough for abstraction in the latter (Figure 16).

 

1 1A. Lowest Energy Geometry of 11 113. 0.4 kcal/mole less stable than 11A
Figure 16. Lowest Energy Conformers of a—Mesitylacetone

The lowest energy geometry of 12 is one with an a-hydrogen eclipsing the
carbonyl (Figure 17). In this geometry, however, the methylene hydrogens are too far to
be abstracted. Global minimizations with dihedral drivers (10° increments) around
benzene-ct-carbon and a-carbon-carbonyl bonds reveal another minimum in which
methylene hydrogens are close enough to be abstracted (d=2.7 A, w=60°). This conformer

is 2.0 kcal/mole higher in energy than the global minimum (Figure 17).

87

 

12A. Lowest Energy Geometry of 12 12B. 2.0 kcal/mole less stable than 12A
Figure 17. Lowest Energy Geometries of a.(2,4,6-Triethylphenyl)acetone

Semiempirical calculations were performed on 13 to show the lowest energy
geometry is one with the (at-phenyl eclipsing the carbonyl. In this geometry, the benzylic

hydrogens closest to the carbonyl is 3.14 A from the oxygen. (Figure 18)

 

Figure 18. Lowest Energy Geometry of a-(2,4,6-Triisopropylphenyl)acetone

Molecular mechanics calculation reveal that in its minimum energy geometry, 14
like OTBBP, has hydrogens on two methyl groups close enough for abstraction. (Figure

19)

88

 

Figure 19. Lowest Energy Geometry of 2-tert—Butyltriflouroacetophenone

Semiempirical calculations at AMI level were performed on 2'-(2,3-Dimethyl-2-
butyl)benzophenone. The lowest energy geometry was calculated to be the one with the
isopropyl group pointing up with its hydrogen pointing over the benzene ring. There are
two hydrogens at an abstractable distance from the carbonyl oxygen, but with different
dihedral angles. The isopropyl hydrogen is closer and better aligned (=2.28 A, m=42.8°)
than the methyl hydrogen (d=2.46 A, (D = 96.4°). Minimizations (semiempirical-AMI
level) were also performed with a dihedral driver (10° increments) for rotation around the
benzene-t-hexyl bond to detect conformations with methyl hydrogens better aligned for
abstraction. The calculations revealed another minimum 1.0 kcal/mole higher in energy
than the global minimum In this conformation, only methyl hydrogens are close enough

for abstraction (d=2.31 A, m=78.9°, Figure 20).

89

 

15A. Lowest Energy Geometry of 15 15B. 1.0 kcal/mole less stable than 15A

Figure 20

Discussion

1. Conformational Control of Product Ratios from Triplet 1,5-

Biradicals

The high diastereoselectivity observed in the photocyclization of a-(o-
alkylphenyl) and a-(2,4,6-trialkylphenyl)acetophenones was attributed to differences in

energy of two hydroxy-biradical rotamers by Park and Wagner.”88

For example, the
observed 20:1 indanol ratio in the photocyclization of a-(o-ethylphenyl)acetophenone

was attributed to a 20:1 population of biradical conformers Brlz and Br”; (Scheme 40).

 

 

 

 

Scheme 40

90

91

Our temperature studies along with semiempirical calculations, however, indicate

that not only activation enthalpies, but also the entropies (the A factors in the Arrhenius

-Ea/RT

equation, k= Ae ), which may reflect the intersystem crossing rates of the biradical

rotamers, are responsible for the observed diastereoselectivities.

Table 23. Effect of Temperature on the Indanol Ratios of a-Arylacetophenones

 

 

 

 

 

 

 

 

 

 

T (°C) solvent 12:“: 22:2E 32:31:? 4ZZ:4ZE 5ZE:5ZE 6Z:6E 82:8E
-72 Toluene 26:1 31:1 44:1 1:9 6:1 0.68:1 23:1
-72 Methanol - - - 0:100 15 :1 - -

0 Toluene 16.5:1 24:1 20:1 1.6:1 1.5:1 1.04:1 16:1
24 SiOz - >30:l >30:] 1:2.5 10:1 1:1 16:1
24 Methanol 2:1 - 5:1 1:] 12:1 - -
24 Crystal >30:l 100:0 - - 100:0 1 :1 -
24 Toluene 14.5:1 21:1 15:1 5:1 1.2:1 1.3:1 10:1
110 Toluene 11.5:1 16:1 10:1 10:1 111.5 1.5:] 4.5:1

 

 

 

 

 

 

 

 

 

 

92

 

4 ITI I rjII I I I I I I l—I I I I l I ITI

lnk

 

 

 

15 #Jlljllllllllllljllllll

2.5 3 3.5 4 4.5
1000/1‘ 5

 

1( ), 2(9) . 3(A), 8(0)

Graph 2. Arrhenius Plot 1

Table 24. Arrhenius Data from Graph 2

 

 

 

 

 

 

Ketone Az/AE AE,, Kcal/mole
I Az/AE = 4.6 EE-EZ = 0.69
2 AZ/AE = 8.2 EE-Ez = 0.55
3 Az/AE = 2.0 EE-EZ = 1.2
8‘l AE/AZ = 7.0 I EE-EZ = 2.4

 

 

 

 

a) from the three lowest points
Product ratios are influenced by the energies and hydrogen abstraction rates of

reactive excited state conformers as well as interconversion and cyclization rates of

93

biradical rotamers. Energies of reactive triplet conformers mirror those of reactive ground
state minima since the only significant change in geometry due to ma" excitation is a
slight lengthening of the C-0 bond.107 The hydrogen abstraction rates are dependent on
the orientation of the abstractable hydrogen relative to the nodal plane of the carbonyl
group95 and are assumed to be similar for various conformers. These factors control the
product ratios only when cyclization is faster than interconversion of biradical rotamers
(ground state control). When biradicals interconvert faster than they cyclize, which is the
case for most triplet biradicals due to their long lifetime, only energies and cyclization
rates of various conformers influence product ratios (conformational control). Thus, in
cases where the photocyclization is conformationally controlled, the product ratios can be
calculated using Equation 4,

me = (xz/XE).(chy./k%y.)
Equation 4

where X2 and XE are the populations of the biradicals leading to Z and E indanols and
kzcyc and kECyc are the rates of the cyclizations for different conformers. The populations
of different rotamers are determined by the difference in their free energies which are
presumed to be dominated by enthalpies. There are several known mechanisms for ISC of
biradicalsg° In short biradicals, ISC is mainly driven by spin-orbit coupling, which is
known to be very much dependent upon the distance and orientation of radical

76.97 ,98 .99
centers.

The observed diastereoselectivities can, thus, be explained by the
calculated energies, which reflect the conformational population, and cyclization rates

which contain the intersystem crossing term. Semiempirical calculations have been

94

performed on the conformational distribution of the hydroxybiradical from 1. In these
calculations, only the biradicals with the methyl at the S-radical site trans to the
hemipinacol radical moiety were considered, since the syn isomer was found to lie 4
kcal/mole above the trans. There are only two minima within 5 kcal/mole of the global
minimum (Brlz). Only one of these conformers (BrlE), which lies 0.5 kcal/mole above the
global minimum, can cyclize directly. The other conformer (Brlx) requires a rotation
around the ethylphenyl ring to achieve a cyclizable geometry. Brlx can form Brlz and
Br”; by small rotations around bonds a and b, respectively. Analysis of the minimization
map reveal that these interconversions have similar barriers such that Br,z (2.3 kcal/mole)
and Br”; (3.1 kcal/mole) are formed in a 3:1 ratio from Brlx. This results in almost the
same population ratio expected form a 0.5 kcal/mole energy difference. Thus, even
though Brlx can not cyclize directly, it acts as a transitional geomtery from which either
one of the two reactive (cyclizable) geometries can be formed. It was also observed that
the rotamer with the hydroxyl group pointing toward the central benzene ring is more
stable (about 1.0-2.0 kcal/mole) than the one with the hydroxy group pointing away. This

100.101 .
and IS

phenomenon represents hydrogen bonding of the OH to the benzene ring
prevented by Lewis base solvents. The large solvent effects on the photobehavior of 1
strongly support such a stabilizing effect in the biradical. In Brm, the two singly occupied
p orbitals are almost orthogonal but not pointed at each other as they are in Brlz. These
different orbital orientations seemingly lead to less triplet-singlet mixing in Br“; and to

less efficient intersystem crossing, which appears as a lower pre-exponential factor for

cyclization (Scheme 41).

95

 

 

 

 

Scheme 41

If we assume that intersystem crossing is independent of cyclization and that at
each minimum the system intersystem crosses to the singlet surface, then we must
determine what happens to Brlx after it becomes a singlet. Since Brlx cannot cyclize
directly, it must convert into either Brlz or BrlE. The calculated rotational barriers noted
above suggest that Brlx can form Brlz 3-times more efficiently than it can BrIE. Boltzman
population ratios of Brlz, Brlx and Br”; are 0.42, 0.42 and 0.16, respectively. If we
assume that Brlz intersystem crosses faster than Brlx and Brlg, due to a better orbital
orientation, the ratio of intersystem crossing rates at room temperature can be measured,
as follows, from the product ratios.

15 =(0-42(kisc1/kisc2)+ 0.28)/(0.16+0.14) thus kiscl/kisc2= 10
Where km, and kisc2 are the intersystem crossing rates of Brlz and Brlx or BrlE,
respectively. This ratio seems too high to arise simply from different orbital orientations.

Thus, it is believed that Brlx converts into Brlz and Br”; prior to intersystem crossing.

96

The fact that 1 yields only Z-indanol in the crystal confirms that Brlz is the
predominant initial biradical geometry and rotations around the hydroxyradical site are
necessary for formation of E-indanol.

Similar explanation can be offered for the photobehavior of 2 at various
temperatures. The Arrhenius plot is linear which indicates that the biradical conformers
are equilibrated at all temperatures. Semiempirical minimizations reveal the presence of
two minima (2A and 2B) within 1.2 kcal/mole of each other. The global minimum 2A is
in the pro-Z geometry while 2B is in the pro-E geometry. The calculated enthalpic

difference between the two biradical rotamers is twice the measured value (Table 24).

 

2A 28. 1.2 kcal/mole less stable than 2A

Figure 21. Lowest Energy Biradical Conformations of 2

It was thought that ground state control might be operative. Global minimizations
of the ground state ketone show the presence of two minima (2C and 2D) within 0.6

kcal/mole of each other, with the global minimum 2C in the pro-Z geometry. However,

97

analysis of the lowest energy rotational path for the interconversion of the two biradical
conformers did not reveal significant barriers (4-5 kcal/mole). Thus, biradical minima can
interconvert and ground state control can not be operative. It is believed that reactivity is
rotationally controlled, with the discrepancy between the calculated and measured values
attributable to over estimation of calculated pro-E energy. The large difference in the A
factors may be attributed to: 1) the pro-Z biradical cyclizing faster than the pro-E
biradical and 2) a larger entropic loss for the pro-E relative to pro-Z biradical due to

phenyl and methyl ending up cis to each other in the E-isomer.

 

2C 2D. 0.6 kcal/mole less stable than 2C
Figure 22. Lowest Energy Ground State Conformations of 2

Arrhenius data for 3 indicate that the conformation leading to 32 should be 1.2
kcal/mole more stable than that one leading to 3E. Our minimizations, however, reveal
the presence of 5 minima within 2 kcal/mole of each other. Three of these (3A, 3B and
3D) are in a pro-Z and the other two (3C and 3E) are in a pro-E geometry. The global
minimum (3A) has the hydroxyradical end twisted away from the benzylic radical such

that cyclization requires a rotation around tolyl-a-carbon bond. Conformations 3B, 3C

98

and 3D are respectively 0.1, 1.0 and 1.3 kcal/mole higher in energy than 3A. The highest
energy conformer (3D) is 2.0 kcal/mole higher than 3A and will not contribute much to
the overall yield of 3indE. Thus, the observed product ratios in case of 3 are the result of
products stemming form three conformations. In all reactive conformers (3B, 3C, and
3D), the two singly occupied p orbitals are orthogonal and are pointing toward each other.
Thus, the A factor ratio simply represents the ratio of number of conformers leading to Z
and B (Table 24). It is worth noting that the measured 1.2 kcal/mole enthalpy difference
reflects an 88:12 ratio of pro-Z: pro-E conformers at RT. This ratio is also achieved by
the Boltzman population of the three calculated conformers [3B(76%), 3C(15%),

3D(9%)].

 

3C. 1.0 kcal/mole less stable than 3A 3D. 1.3 kcal/mole less stable than 3A

 

3E. 2.0 kcal/mole less stable than 3A
Figure 23. Lowest Energy Biradical Conformations of 3

The Arrhenius plot of 8 is curved. It was thought that the curvature could be
associated with the dehydration of indanols at high temperatures, thus leading to
erroneous product ratios. However, control experiments revealed that dehydrations do not
occur during the timeline of irradiations. This curvature can, however, be explained by
one of the following:
1) A curved Arrhenius plot means a change in the mechanism of the reaction. Thus the
curvature can be attributed to a change in the factors that control the reactivity. The
measured isomeric ratio at -72°C is much less than the expected value predicted by the
line through the other three points. Therefore, it is reasonable to assume that a mechanism
other than conformational control is operative. The stereoselectivity of 8 depends on
geometric variations at the a-hydroxy radical site. Rotation of the mesityl ring is too slow

3°g"°2 If rotations around the a-

to compete with biradical decay at low temperatures.
carbon-hydroxyradical site are also slow (semiempirical calculations show a 6.0
kcal/mole barrier), then the biradical must react from the geometry in which it is formed

and ground state control becomes operative. Semiempirical minimizations have revealed

the presence of two reactive ground state minima; with the low energy minimtun in a pro-

100

Z and the high energy one in the pro-E geometry. The difference in energy of 2.1
kcal/mole, however, warrants a Z:E ratio of 250:1, much greater than the 25:1 observed
ratio. The 10-fold contrast between calculated and measured ratios can, however, be
attributed to the difference in partitioning of the resulting biradicals, with the pro-E
biradical cyclizing 10-times more efficiently than the pro-Z. Indeed, the ratio of A factors

shows that the pro-E biradical cyclizes 7-times more efficiently than the pro-Z biradical.

 

8A. Lowest Energy Geometry of 8 SE. 2.1 kcal/mole less stable than 8A
Figure 24. Lowest Energy Ground State Conformations of 8

2) Global minimizations on the hydroxybiradical from 8 reveal the presence of 4 minima
within 1.0 kcal/mole of each other. Three of these conformations (8C, 8D, 8E) are in a
pro-Z geometry. Of these conformations, 8E has the hydroxyradical end twisted away
from the benzylic radical such that cyclization requires 180° rotation around the mesityl-
a-carbon bond. It was mentioned earlier that this rotation is too slow to compete with
biradical decay at low temperatures, as seen from variable temperature NMR which
shows coalescence of the ortho-methyl groups of 8 near 0°C. Thus, even though

cyclization is possible from SE and 8G above 0°C, it can not happen at -72°C which

101

should lead to a lower than expected Z:E ratio at this temperature. This explanation,
however, can be disregarded if one considers the rotational map that shows the
interconversion of these conformers. Conversion of 8C, which is essentially the initial
biradical geometry, to the other conformers suffers from relatively high barriers (6-9 '
kcal/mole). This means that at low temperatures biradical interconversion can not

compete with cyclization which in turn means that ground state control is operative.

 

SE. 0.7 kcal/mole less stable than 8C 8F. 0.8 kcal/mole less stable than 8C

Figure 25. Lowest Energy Biradical Conformations of 8

102

 

 

 

 

32
30 _ '
E {l u
g 23 _
¢ ' . .I _ 'i -
fi 25 _ .- -. '1' ".1 ‘1'.
V . | I; ,|' .3
2 - '. '2‘ n _
I-l-l . ' .h . '1'.
22 - ' ' '
8E '. /' " 8D
20 r 1 r r A
-4 -2 0 2 4 6 8
Lowest Energy Rotational Path

Photobehavior of 8 at higher temperatures is assumed to be conformationally
controlled. The Arrhenius data indicate the pro-Z biradical to be 2.4 kcal/mole more
stable than the pro-E. This gives a 2: E population ratio of 98:2. Our calculations,
however, indicate a lower population ratio of 85:15 based on the energies of cyclizable
minima 8C, 8D and BF. This discrepency may be attributed to competition between
ground state and biradical controls at 0°C (since it is not clear at what point the plot starts
to curve, one can not be sure of such competition). The difference in the A factors is

attributed to a more efficient cyclization of the pro-E conformer.

103

 

3 I I I r TI I I I l I I I I I I I I I I I I I I

N
IIIIlIIII
;[>
1/
i

Ink
0

 

 

 

3llllllllllllllllllllllll
-

 

2.5 3 3.5 4 4.5
1000/T 5
4 (0). 5(A), 6(X)
Graph 3. Arrhenius Plot 2

Table 25. Arrhenius Data from Graph 3

 

 

 

 

 

Ketone Az/AE AF.” Kcal/mole
4a All/A25 = 2325 Ezs'Ezz = 4.0
5 AEZ/AZE= 18.8 EEZ'EZE = 1.88
6 AZ/AE = 3.7 Ez-EE = 0.67

 

 

 

a) from the best-fit line
The lack of stereoselectivity in photocyclization of 6 is similar to earlier results

from the Wagner group.5°"°3 The two biradical geometries with phenyl tilted up or down

 

104

are very similar in energy but have different orbital orientations which leads to different

cyclization rates (Scheme 42).

 

Scheme 42. Lowest Energy Biradical Conformations of 6

Arrhenius data for 5 indicate the pro-ZE precursor to be enthalpically more stable
than the pro-EZ one by 1.88 kcal/mole. Global minimizations on the biradical from 5
reveal the presence of 3 minima within 0.5 kcal/mole of each other. The global
minimum(5A) is in a pro-EZ while the other two (SB and 5C) are in a pro-ZE geometries.
The fact that the global minimum has a pro-EZ geometry contrasts with the Arrhenius
data. Another interesting observation is that the Arrhenius plot of 5, unlike 8, is not
curved. The curvature in the plot of 8 was rationalized in terms of either 1) ground state
control or 2) lack of cyclization of several biradical conformations. Option 2 is not valid
for 5 since the next closest minimum is 2.4 kcal/mole higher in energy than 5A and will
not contribute much to the product ratios. This suggests that photobehavior of 5 is ground

state controlled. The rotational energy map for interconversion of 5A to SB indicates an

105

11 kcal/mole barrier. This barrier is much too large for the interconversion of these
biradical conformers to compete with cyclization. Thus, ground state control of reactivity

must be operative.

 

5C. 0.5 kcal/mole less stable than 5A

Figure 26. Lowest Energy Biradical Conformations of 5

Semiempirical minimizations on the ground state of 5 revealed two minima (5E
and SF) within 1.8 kcal/mole of each other. If bond rotations are slow as expected and
ground state control is operative, then these geometries should give the products in the

correct ratios. Arrhenius data predict the two reactive geometries to be different in energy

106

by 1.88 kcal/mole (good agreement with calculated results) with the lower energy
geometry resulting in the ZE-isomer. Indeed, the global ground state minimum is in the

pro ZE-geometry.

eelc_energy
7.08 to
18.98 keel .tnole

5A 53

Energy (kcalJ mole)

 

 

Lowest Energy Rotational Path

The difference in the A factors is attributed to the difference in rotational
entropies of the two conformers. The pro-ZE conformer has a higher rotational. fieedom
than the pro-EZ conformer since in the latter phenyl and methyl are cis (gauche) to each
other. Thus, for the ground state control of reactivity, interconversion of the pro-EZ
conformer to the pro-ZE one is entropically favored while the reverse is entropically

disfavored. The fact that quantum efficiencies of formation for the ZE (0.14) and El

107

indanols (0.12) are similar indicates that the pro-EZ biradical is cyclizing more

efficiently.

 

5E 5F. 1.8 kcal/mole less stable than 5E

Figure 27. Lowest Energy Ground State Conformations of 5

The photobehavior of 4 is striking in that the ZE isomer, the minor indanol
formed at room temperature, is the predominant product at low temperatures in
hydrocarbon solvents and is the only product at low temperature in methanol. The
Arrhenius plot of 4 ,similar to that of 8, is curved. Furthermore, the Arrhenius data
obtained from the best fit line have unrealistic values of AB, and A for an equilibrated
system. The data would indicate the pro-ZE biradical to be more stable than the pro-ZZ
by 4.0 kcal/mole. Global minimizations on the biradical of 4, however, show the global
minimum to have a pro-ZZ geometry, with the closest cyclizable pro-ZE biradical (4D)

1.5 kcal/mole higher in energy.

108

 

4C. 0.5 kcal/mole less stable than 4A 4D. 1.5 kcal/mole less stable than 4A
Figure 28. Lowest Energy Biradical Conformations of 4

The curvature in the plot is believed to involve competition between bond rotation
and cyclization in the hydroxybiradical at low temperatures. The lowest energy rotational
map for interconversion of these biradical conformers shows 4-10 kcal/mole barriers. At
low temperatures slow bond rotation in the biradical can not compete with cyclization, as

in S and 8, and ground state control is operative. As temperature increases, the rotation

109

becomes faster and competes with cyclization. At or near room temperature, rotation

becomes faster than cyclization and conformational control takes over.

30

 

 

 

 

23 ~

25 _.
i 24 ~
5
E 20 L
'5 18 P

16 l- _

m
,4 4n 3‘3 . 4B
0 5 1o 15 20
LowestEmgyRombmlPath

The ZE:ZZ ratio of 9:1 at -72°C thus must be the result of the ground state
control. Global minimizations on ground state of 4 reveal the presence of two minima
within 1.0 kcal/mole of each other, with the lower energy one being in the pro-ZE
geometry. It is thus believed thatithese two conformers are responsible for the observed

9:1 ZE:ZZ ratio at -72°C.

 

4E 4F. 1.0 kcal/mole less stable than 4E

Figure 29. Lowest Energy Ground State Conformations of 4

110

The low quantum efficiency for cyclization (0.06) in 4 is attributed to a competing on-
cleavage reaction and an efficient back transfer which occurs at geometries along the
rotational path of interconversion of calculated minima.

Finally, the absence of the EZ-isomer from photoproducts of 4 can be explained
by considering that the lowest energy biradical conformer leading to El lies 2.2

kcal/mole above the global minimum and thus is scarcely populated.

 

4G. Pro-EZ biradical

H. Photobehavior of a-Arylacetones - A Comparison of Singlet and

Triplet Biradical Behavior

The main goal of this project was to determine the similarities and differences in
reactivity and selectivity of 1,5-singlet and triplet biradicals. From a mechanistic point of
view, the difference in the reactivity of the singlet and triplet 1,5-biradicals and the role
of environmental and conformational factors in determining the overall efficiency and
chemical yield of indanol formation must be addressed.

As mentioned earlier, the reactive excited states for aliphatic ketones are both
singlet and triplet states. Thus, the excited states responsible for the two observed

photoreactions in a-arylacetones, namely S-hydrogen abstraction and a-cleavage, have to

111

be determined. Turro has shown that in a-(o-tolyl)acetones S-hydrogen abstraction occurs
only from the singlet while (rt-cleavage occurs only from the triplet.67 Our quenching

studies corroborate Turro’s results.

Table 26. Effect of Temperature on Product Ratios from a-Arylacetones

 

 

 

 

 

 

Compound Indanol/Diarylethane Indanol/Diarylethane Indanol/Diarylethane
-72 °C 24 °C 1 10°C
10 20:80 50:50 (3:1-Z:E) 60:40 (1.4:1 Z:E)
11 0:100 60:40 70:30
12 15:85 70:30 (10:1-Z:E) 85:15
13 0:100 70:30 100:0

 

 

 

 

 

Temperature effects on quantum yields are quite interesting. Diphenylethanes
(DPEs) are the major and sometimes the only products at low temperature while indanol
yields increase with increasing temperature. The high yield of DPEs, which result from
(rt-cleavage followed by coupling of the resulting free radicals, demonstrates that there is
an enthalpic barrier to hydrogen abstraction at low temperature whereas intersystem
crossing has none. Thus, as temperature decreases, intersystem crossing to the triplet
which only ot-cleaves becomes predominant. Indanol yield increases with increasing
temperature. This may be due to two reasons: First, a higher population of excited

singlets undergoing hydrogen abstraction because they have higher kinetic energy; and

112

second, a higher percent of the resulting singlet biradicals cyclizing rather than
disproportionating. The latter would support Wagner’s suggestion that cyclization
reactions have large barriers (due to loss of rotational freedom, ring strain and steric
crowding around the forming bond) even on the singlet surface.87

The decrease in the quantum efficiencies of indanol formation in the trialkyl series
from mesityl to the triisopropyl can be attributed to an increasingly more efficient
disproportionation of the singlet biradical as the size of the alkyl group increases (which
impedes cyclization due to increased strain during cyclization).

Wagner er al. reported that a-mesitylacetophenone has a more rapid hydrogen
abstraction but a lower indanol quantum yield than a-(o-tolyl)acetophenone, which they
attributed to a charge-transfer quenching process competing with hydrogen abstraction in
the former.87 An increase in indanol quantum yield in the acetone series from a-tolyl to
a-(o-ethylphenyl) to a-mesitylacetone indicates the absence of any significant charge
transfer quenching process from the singlet state.

The effect of environment on the reactivity of acetones has also been addressed by
Turro67 who reports a significant increase in indanol chemical yield in micellar solutions
relative to homogeneous solutions. Our results show a 25% increase in indanol yield in
micellar solutions.

The conformational factors involved in hydrogen abstraction of or-arylacetones
might be expected to be similar to those for a-arylacetophenones. However, a 2-6 fold

decrease in diastereoselectivity was observed in acetones.

113

 

1.2 I I I I I I I I I I I r I I I I 1 I I l I I I

lnk

 

 

 

0.2 11111111111111111111111

2.6 2.8 3 3.2 3.4 3.6 3.8
1000/T

 

AE/AZ=5 EZ'EE= 1.6 kcal/mOle
Graph 4. Arrhenius Plot of a-(o-Ethylphenyl)acetone

The singlet biradicals have very short lifetimes and the ground state control might
be assumed to control their reactivity. However, our results with a-(o-ethylphenyl)
acetone seem to indicate conformational control of reactivity in photocyclization of
singlet biradicals. Experimental results show the Z-indanol to be the major cyclization
product under all conditions. Ground state global minimizations indicate the presence of
two reactive geometries, a low energy in a pro-E and a pro-Z geometry 0.55 kcal/mole
higher in energy (Scheme 43). Furthermore, semiempirical minimizations on the biradical
of 10 show the presence of three minima within 1.8 kcal/mole of each other. The global

minimum (10A) is not in a good geometry to cyclize, but the two higher energy

114

conformations can and are in a pro-Z (10B) and pro-E (10C) geometries, an can cyclize.
10C is higher in energy than 10B by 1.6 kcal/mole, in good agreement with the
experimental values. The difference in A factors can be attributed to a faster cyclization
rate of the pro-E precursor, due to its higher energy which in turn means a lower
activation energy for cyclization. Therefore, the photocyclization of (X-(2-
ethylphenyl)acetone is believed to be conformationally controlled which means that the
singlet biradical lives long enough to allow equilibration. Furthermore, the difference in

the A factors indicates that there needs to be an activation energy for cyclization.

 

10C. 1.6 kcal/mole less stable than 10A

Figure 30. Lowest Energy Biradical Conformations of 10

115

Another explanation for the observed diastereoselectivity is that ground state
control is operative but the pro-E biradical disproportionates 9 times more efficiently than
the pro-Z biradical. This could be the case since the cyclization of the pro-E biradical

suffers from larger steric/non-bonded interactions during the closure than the pro-Z.

   

Pro-E PTO-Z

Scheme 43. Reactive Ground State Conformations of 10

III. Photoenolizations of a-(2,4,6-Triisopropylphenyl)acetophenone and

Acetone

Formation of enol from compound 9 had already been documented.°°°’°°'87 Our

reinvestigation of this reaction along with temperature and phase effects indicate that the
enol is the only initial product formed under all conditions. Furthermore, our
investigation into the photobehavior of a—(2,4,6-triisopropylphenyl)acetone (13) reveals
that enol formation also occurs from the singlet states. We have demonstrated that in both
cases enol photochemically and thermally reverts back to ketone. Thus the formation of
enol and its reversion to ketone with hydrogen exchange between the benzylic and a—
carbons demonstrates that disproportionation involving a 1,4-hydrogen transfer can
compete with cyclization. The large preference for formation of enols from 9 and 13

might be blamed on the normal steric hindrance to cyclization of two tertiary radical sites.

116

However, since ot-(2,5-diisopropylphenyl)acetophenone cyclizes quite efficiently, the

36 37 . . .
°‘ The semiempirical

effect of the second o-isopropyl group warrants scrutiny.
calculations strongly suggest that the other isopropyl group forces the biradical into a
geometry in which one a-hydrogen is pointed directly at the other radical site, thus
inviting disproportionation. Cyclization, on the other hand, requires bond rotation which
may be impeded by the second isopropyl. The fact that enol is the only product at low
temperature and from crystalline 9 demands that the indanol-forming biradical
conformation be different from that initially formed. The minimized geometries of
ketones 9 and 13 lead to the minimum energy biradical geometries, which favor

disproportionation, as just noted. For this reason, the singlet and triplet biradicals behave

very similarly.

 

Figure 31. Lowest Energy Ground State and Biradical Conformers of 9 and 13

117

An explanation is required for the fact that the enol is a stable product at long
wavelength irradiation but not at shorter wavelengths. A solution containing only enols,
obtained by low temperature irradiation, showed strong UV absorption below 330 nm,
with km, near 270 nm. Initially, the indanol is formed in low yield but the yield increases
with conversion. This means that enol is converted photochemically to indanol, and is in
agreement with the observed decrease in enol quantum yield with time for irradiations at
wavelengths where the enol absorbs strongly. Our time dependent studies for irradiation
of both ketone and enol show that indanol is not formed directly from enol but only from
ketone, which must be regenerated continually from the enol. The mechanism of this
disproportionation is unclear. Hart has proposed a simple 1,3-hydrogen shift, which
seems reasonable even though the trimethylsilyl enol ether of 9 does not undergo the
same 1,3-shift.

For ketone 13, (at-cleavage is the only photoreaction at low temperature. This
demonstrates that there is an enthalpic barrier to hydrogen abstraction, whereas
intersystem crossing has none. Thus, as temperature decreases, the intersystem crossing
to a triplet that undergoes only radical cleavage becomes predominant. The overall
quantum efficiency is low for 13 because of the well known highly efficient radiationless
decay that accompanies singlet state hydrogen transfers.11 The stability of solid 13 is
attributed to the large ground state C=O---H distance (3.2 A).

We have considered the possibility of similar enol formation for the other a-aryl
acetones and acetophenones studied. In our investigations, however, we were unable to

detect any, except maybe for a-(2,4,6—triethylphenyl)acetone where a vinyl peak was

118

observed in the NMR spectrum of the photolysis mixture but disappeared too quickly to
allow careful analysis. The less hindered enols are expected to be much less stable with

respect to ketone and if formed apparently are too short-lived to detect.

IV. Photobehavior of o-tert-Butyltrifluoroacetophenone

Wagner et al. reported a sharp contrast in the photobehavior of o-tert-

54.56 . . .
Irradiation of benzophenones results in

butylacetophenones and benzophenones.
efficient formation of indanols while that of acetophenones results mainly in an
unsaturated alcohol. Rotation of the 1,5-biradical produced by 6-hydrogen abstraction in
o-tert—butylphenyl ketones is necessary for cyclization but destroys the benzylic
conjugation. n—Conjugation is more important in excited states than in ground state.'°4 In
the benzophenone derivatives, the benzylic radical center of the biradical can remain
unconjugated with the unsubstituted phenyl ring while the butylphenyl ring rotates. The
absence of the second phenyl ring in the acetophenone derivatives causes a retarded
rotation. Thus, the difference in behavior was attributed to the retarded rotation of the
benzylic center of the biradical which slows down the indanol formation and allows the
biradical to undergo a less favorable reaction, namely rearrangement to an unsaturated
alcohol. The authors cited two possibilities for the formation of the unsaturated alcohol,

disproportionation of a rearranged 1,5-biradical or a 1,5-sigmatropic hydrogen shift in a

. 54
sprroenol.

119

 

Scheme 44

The photobehavior of o-tert-butyltriflouroacetophenone was investigated to
determine whether the capto-dative resonance of the benzylic radical center to the
trifluromethyl group is sufficient to allow a free rotation of the benzylic center, leading to
an indanol as a major product.

OH +°OH

\ CF3 Cl:2

 

/

Scheme 45

Our results clearly indicate that capto-dative resonance is not sufficient to allow a

free rotation of the benzylic radical center since the unsaturated alcohol comprised ~90%

120

of the products in all solvents. Our calculated barrier to rotation of the benzylic radical
center of acetophenone and triflouroacetophenone totally out of conjugation is 8
kcal/mole. If the benzylic center has to rotate only 45° to get into a geometry suitable for
cyclization the barrier drops to 4 kcal/mole. Clearly, capto-dative resonance does not
provide 4 kcal/mole stabilization to speed up cyclization process, thus the less favorable

rearrangement to unsaturated alcohol remains the predominant relaxation pathway.

 

90%

Scheme 46

V. Photobehavior of 2-(2’-(2’,3’-Dimethylbutyl))benzophenone - Effect

of Dihedral Angle on Hydrogen Abstraction Rates

The primary purpose of this study was to gain insight into the orbital orientational
requirements for hydrogen abstraction by triplet carbonyls.

Global minimizations (AMI) with dihedral drivers around phenyl-tert-carbon
bond have revealed the presence of two distinct minima on the energy surface of 15

. (Figure 32). The lowest energy minimum (15A) has the isopropyl group perpendicular to

121

the plane of the phenyl and occupying the same side of the plane as the carbonyl oxygen.
In this geometry both isopropyl (HA, d= 2.3 A) and methyl hydrogens (H3, d= 2.5 A) are
close enough for abstraction. In the other minimum (15B), which lies 1.0 kcal/mole
above ISA, only methyl hydrogens (d=2.3 A) are close enough for abstraction. The global

minimum 15A has a geometry similar to the X-ray structure of OTAMBP.57

 

15A. Lowest Energy Geometry of 15 15B. 1.0 kcal/mole less stable than 15A
Figure 32

Our calculations have revealed that a methyl hydrogen is within abstraction

105
has

distance of the carbonyl oxygen over a wide range of geometries. Scheffer
established that distance is the principal determinant of reactivity,‘06 so the reaction can
occur from a geometry other than the two minima. However, the very low activation
energy for triplet decay in OTBBP5° rules out more than slight departures from
conformational minima in reaching the transition state. Despite favorable distances, the

methyl hydrogens have different dihedral angles with respect to the nodal plane of the

carbonyl in the two minima. In 15A, the angle to is 96° while in 158 (o is 79°. If we

122

consider a Coszo) dependence on reactivity, as has been proposed by Wagner,48 methyl
hydrogens in both conformations should be unreactive toward abstraction. Despite this,
15 forms indanol photoproducts that represent 50-90% hydrogen abstraction from a
poorly positioned methyl group. Even in the crystalline state 50% of the products
originate from methyl abstraction. It is conceivable that the flexibility of the tert-hexyl
group might cause significant improvements in a) at the transition state relative to the
reactant. It is also noteworthy that the reactant is the triplet, not the ground state on which
the calculations have been performed. This, however, shouldn’t alter our treatment since

the only significant change in geometry due to n,rt* excitation is slight lengthening of the
C-0 bond. ‘07

Biradical Partitioning. The quantitative treatment of our results involves converting
product ratios into relative rate constants for hydrogen abstraction. Scheme 47 depicts the
competition that produces the observed product ratios. The product ratios are determined
by the ratios of hydrogen abstraction rates times the partitioning of biradical between
coupling and reversion back to ketone. An extra feature of the photobehavior of 15 is the
formation of 15alc. To our knowledge, such intermediates (spiro-intermediate) and
photoproducts have been observed for o-alkoxy and o-tert-butylacetophenones but not
benzophenones.54 Formation of the unsaturated alcohol from a spiro intermediate in 2,4-
di-tert-butylacetophenone has quantum efficiencies of 0.02—0.05 in benzene and
methanol.54 Thus, the biradical and the spiro intermediate revert back to starting ketone

with a combined 95-98% efficiency.

123

 

   

    

 

 

 

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hv v
\ ————>
Ph C D
D 6 6
C6 6 l /
rs
H30 C2; H30 9H3 H30 CH3
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/ . + ., CH3
How"Ph Ho"Ph ”0 Ph
\ 15alc lSindmZ 15:..de k lSindip ,
Y
1" Radical Products 3° Radical Products
Scheme 47

If one considers that the biradical from OTBBP forms the indanol product with a
quantum efficiency of 1 and that both biradicals from OTBBP and 2,4-di-tert-
butylacetophenone are solvated to the same extent, we can conclude that all of the 95%
disproportionation back to ketone in methanol arises from the spiro intermediate.
However, such values are not available for benzophenone derivatives and the mechanism
of reversion of the spiro-intermediate back to ketone (radical or ionic) is unknown. Thus,
for simplicity, two boundary conditions have been considered:

a) The spiro-intermediate which leads to formation of 15alc has a quantum efficiency of 1
for product formation, so that all partitioning is presumed to occur in the biradical. Thus

product ratios can be determined using Equation 5.

l/3=(15indmZ + 15inde + 15alc ) / lSindip = (kmeH / kip") (PB,,/ Pm)

Equation 5

124

One must understand how the PB,,/ Pm ratio can vary in order to correctly deduce
km,“ / kip” ratios from product ratios. There is a large solvent effect on product ratios and

quantum efficiencies.

Table 27. Effect of temperature and Medium on Product Ratios of 15

 

 

 

 

 

 

 

Reaction T (° C) 15indmZ lSinde 15alc 15indip
media
Benzene 24 27 52 7 1 5
Methanol 24 32 32 l 3 23
Toluene 1 10 22 29 8 41
Toluene -72 33 48 5 15
solid 24 23 27 - 50

 

 

 

 

 

 

 

This solvent effect shows that the two biradicals cyclize with different
efficiencies. In benzene, all biradicals from OTBBP, OTAMBP and 15 disproportionate
to starting ketone with high efficiency. In methanol, all of the biradicals from OTBBP
cyclize but not quite half of those from OTAMBP and 15 cyclize. The P3, value for the
biradical from OTBBP is 0.04 in benzene but rises to unity in methanol, where hydrogen
bonding to solvent suppresses biradical disproportionation back to the ground state
ketone. Similarly, the PB, value for a solvated biradical is unity in OTAMBP, while those
for unsolvated biradicals are 0.05 and 0.028 for a primary (methyl) and secondary (ethyl)

radicals, respectively. The low quantum yields for 15 and the methanol induced increase

125

in the yield of lSindip suggest that P3,, cyclizes less efficiently than does PB”. The fact
that Pm is more sterically crowded than P3,, will lead to a lower rate of cyclization in
unsolvated biradicals. This point will be emphasized when the temperature effects on
product ratios are considered.

Since methanol increases the total quantum yield of 15 only to 42%, its biradicals,
similar to those of OTAMBP, hydrogen bond to solvent less efficiently than the less
sterically crowded biradical of OTBBP. Because methanol traps only 42% of biradicals,
we rely on an estimate of Br3/Br. for the 58% that still revert to starting ketone. We have
assumed two boundary conditions, described below, in order to calculate the ratios of
hydrogen abstraction rates.

One option is to assume that all primary biradicals cyclize with 100% efficiency
in methanol as is the case for the biradical from OTBBP. In this case, Br3/Brl is 2.2 and
Pad/P3,, becomes 6 and 19 in methanol and benzene, respectively. Therefore, kHip/kac is
calculated to be 2.24 methanol and benzene. However, this treatment would demand an
unlikely P3,, value of 0.27 in benzene, seven times higher than that of OTBBP (PB,= 0.04
in benzene).

(Dubmmfi 0.0835 (Dumflmolfi 0.309 (Dnmmefi 0.01 (Dzmctmol): 0.107
Br,/Br,= 69/31= 2.2
In Methanol: Pan/Parf 1/0.155= 6.45 kmp/kflm= 2.24

In Benzene: PBrl/P8r3= 0.27/0.015= 18.75 kHip/kflm= 2.24

Scheme 48

126

Another option is to assume that the ka/kae is the same as the product ratios.
Partial suppression of disproportionation is common in bulky hydroxybiradicals and is
thought to reflect an equilibrium between hydrogen-bonded and free biradicals, with none
of the former disproportionating. Since Br, and Br3 share a common conformational
preference, the equilibrium constant for solvation should be similar for both biradicals
and the Br3/Br1 ratio should approximate kHip/kac. In this situation, P3,, and PM, become
0.108 and 0.05 respectively for the unsolvated biradicals. It is important to note that

~95% of the reaction in methanol arises from the solvated biradicals.

(Dubenzene): 0°0835 (blflnetllanol): 0309 ¢2(benzene)= 0'01 (Dzuncthanol): 0°107

kaJkHip=77/23

In Methanol: ¢ll¢3=(77/23){0.34+0.67(0.108)/0.34+0.66(0.05)}= 0.309/0.107
In Benzene: (I),/<D3=(77/23)(0.108/0.05)= 0.0835/0.01
Scheme 49

b) It has been assumed that ~90% of the spiro intermediate formed in methanol reverts to
the starting ketone, similar to the acetophenone derivatives. The percent of biradicals
which form indanol becomes 39% and the efficiency of indanol formation from this
fraction is 0.91 if one considers that all solvated primary biradicals form product with

100% efficiency. The kae/kflip value is 1.78 in benzene and methanol.

(bliudflrenzcnc)= 0°0775 (plinmmethanol): 0'248 (D2(benzene)= 0'01 (1)2(methanol): 0°107

¢I,Salc(benzene)= 0'0“ (DISalcmethanoI): 0°06] PBr-spirdmethanol)= 0'61

127

PB,-,,,,,,,,,,,,.,= 059 o,,,,(m,,,,,,.,= 0.355 Efficiency=0.355/0.39=0.9l

Br,/Br,= 25/15= 1.78

In Methanol: Pan/Parf 1/0.75= 1.34 kmp/kflm= 1.78
In Benzene: PBrIIPBr3= 0.31/0.07: 18.75 .kHip/kae= 1.78
Scheme 50

The high efficiency of indanol formation in methanol for 15 is similar to that of
OTBBP.5° The low quantum yields for product formation in OTAMBP relative to
OTBBP was surprising and no products arising from the spiro intermediate was observed.
However, based on our results from 15, an explanation for the low observed quantum
efficiencies in OTAMBP can be offered. It is believed that spiro intermediate is indeed
formed in OTAMBP, but that it disproportionates back to ketone with a higher efficiency
than 15, and thus no products stemming from the spiro compound could be observed.
Formation of the spiro intermediate from the biradical only allows a fraction of biradicals
to be available for cyclization. It is also believed that this fraction is very close to the
observed quantum yield of 0.42 and that the indanol formation from solvated biradicals is
highly efficient.

Temperature Effects. The lack of change in product ratios as temperature decreases
indicates that hydrogen abstraction is derived by relief of steric strain, as proposed by
Wagner, rather than by intrinsic CH reactivity.57 The fact that the amount of 15indip
increases 3-fold at high temperature but is unchanged at low temperature, reflects a
higher efficiency of tertiary biradical closure at higher temperatures. It is, however,

conceivable that changes in conformational equilibria can affect the observed relative

128

”"°8 For example if ISB, in WhiCh only a methyl can

rates for hydrogen abstraction.
react, is slightly lower in energy in certain solvents (due to solvation) than ISA, then the
1/3 ratio would increase with change in solvent provided that no change in P values also
occur. This effect along with changes in P values due to solvation can account for
different 1/3 ratios in methanol and toluene.

Phase Effects. Lower selectivity is observed in the crystal than in solution. The solid
state product ratios can not easily be converted into kae/kHip ratios, since quantum
efficiencies and biradical lifetimes are not available in the solid. If all biradicals have
similar PB, values, then kHip/kflmfi 1.0. If the tert-hexyl rotation is slow in the solid, then
the competition between rotation of Br2 into a geometry necessary for cyclization and
disproportionation back to ketone may be even less favorable than in solution, where
bond rotations are rapid but cyclization is only 2-5% efficient. Since Br, does not need to
rotate, its partitioning should be independent of the environment. The solvent effects on
product ratios suggest different biradical partitioning efficiencies, thus kHip/kae should
be much higher than unity and closer to the solution values.

Diastereoselectivity. The lower diastereoselectivity of Br, in methanol is attributed to the
solvation of hydroxy biradicals to Lewis bases which is known to greatly influence the
diastereoselectivity of their cyclization. A variety of 1,4- and 1,5-biradicals that show
significant preferences for cyclizing with alkyl group trans to phenyl in hydrocarbon
solvents show reduced selectivity in alcohols.33’°°"°9"lo Br. shows a large 2.0 E/Z

selectivity in benzene and toluene but almost no selectivity in methanol. In solid, the

observed selectivity always reflects a least-motion picture of biradical cyclization and in

129

H The general

most cases shows enhanced diastereoselectivity relative to solution.1
conclusion is that low molecular flexibility in crystals may reduce but not totally prevent
inversion of radical sites by rotation. Br], however, does not show an appreciable
selectivity in solid. This can be explained in two ways: either photochemistry occurs at
defect sites or the tert-hexyl bond rotations in solid are faster than biradical cyclization.
The lower 1/3 ratio in solid compared to solution reinforces our assumption that
bond rotations in solid are faster than cyclization. In the solid, one would expect Pm to
be lower than solution due to rotations necessary for cyclization, thus the significant
amount of 3 obtained in the solid either reflects a higher hydrogen abstraction rate,
similar bond rotation rates as solution, or a combination of both. The higher hydrogen
abstraction rates in solid may reflect predominant population of 15A in which isopropyl
hydrogen is in good geometry for abstraction. One would expect 15A to be the
predominant conformation at low temperature in solution as well, however, theratios of
1/3 did not change much from those at room temperature. Since we don’t know the effect
of solvation on various conformations, we tentatively suggest that a combination of
predominant population of 15A and fast bond rotations is responsible for the low 1/3
ratios in solid. The apparent absence of 15alc may represent a topochemically
unfavorable reaction for formation of spiro intermediate.
Our results indicate that significant amount of reaction takes place at methyl hydrogen
oriented at w= 90° at ground state. It is possible, however, that conformational flexibility

causes w<90° in solution and to a lesser extent in solid. In order to better address the

effect of dihedral angle on hydrogen abstraction rates, molecules with low molecular

130

flexibility with hydrogens at m=90° angles with respect to nodal plane of carbonyl need
be synthesized. A few examples of such molecules are given below:

P“ 0 Ph 0

Experimental

1. General Procedures

1H and 13C NMR spectra were obtained using either a 300 MHz Varian Gemini, a
300 MHz Varian VXR-300 or a 500 MHz Varian VXR-500 instrument. IR spectra were
recorded using solutions in C0,, or CHC13 on a Nicolet IR-42 Fourier Transform IR
spectrometer. UV spectra were recorded on a Shimadzu UV-160 spectrometer. Low
resolution mass spectra were recorded on a Hewlett-Packard 5890 GC/MS Trio-I and
high resolution mass spectra were obtained using a Joel JMS-HXI 10 Mass spectrometer
in the MSU Mass Spectroscopic facility. The electron impact (E1) and direct probe
methods were used.

Gas chromatographic analyses were performed on a Varian 1400 or 3400 machine
with flame ionization detectors. The GC was connected to a Hewlett-Packard 3393A or
3392A Integrating recorder. Two types of columns were used for GC analysis; Megabore
DB1 and Megabore DB225. HPLC analyses were performed on a Rainin apparatus
equipped with a Dynamax UV-D absorbance detector using a silica column. For the
preparative TLC, Analtech Uniplate silica gel plates (20 x 20 cm, 1000 micron) were

used.

131

132
II. Preparation of Starting Ketones

a-(2-Ethylphenyl)-B,B,B-trideuteropropiophenone (4d3)
a-(2-Ethylphenyl)-B,B,B-trideuteropropiophenone was prepared by the reaction of

the phenyl Grignard reagent with o-ethylphenyl-B,B,B-propionitrile following the route

given below. Attempts to make this compound from (rt-(2-ethylphenyl)acetophenone,

LDA and methyl iodide resulted in O-methylation.

/

\

HLiAIH4

 

 

CH 20 CHZCI
HHCl or
SOCIZ

NaCN
DMSO

1. PhLi or PhMgBr 1. LDA CH20N
2. H’, A 00 2. 0031

Scheme 51. Synthesis of a-(Z-Ethylphenyl)propiophenone

O /
Ci.
Q:

/

'C

CD,

 

 

2-Ethyl benzoic acid

In a 250 mL three necked round bottom flask equipped with a condenser and
purged with argon was placed 2.0 grams (0.085 moles) of oven dried magnesium and 10
mL of freshly distilled ether. A solution of 2-ethylbromobenzene (13 g, 0.07 moles,
Aldrich) in ether was added dropwise over a period of an hour to the magnesium. The

reaction was initiated with a heat gun or by adding small amounts of 1,2-dibromoethane.

133

After the addition was complete, the mixture was allowed to stir at room temperature for
an hour and was refluxed for two hours to ensure the Grignard formation. A large excess
of dry ice was completely ground with a pestle. After the Grignard had cooled to room
temperature, it was poured into a flask containing the freshly ground dry ice. The
resulting slush was stirred vigorously and was allowed to warm to room temperature. The
work-up consisted of adding 50 mL of 10% HCl to the mixture and separating the layers.
The organic layer was then washed with water and dilute alkali solution. The alkaline
layer was acidified with 10% HCl solution until a white precipitate could be observed.
The precipitate was extracted into ether, and the ether layer was washed twice with water
and dried over anhydrous magnesium sulfate. Solvent was removed to afford 6.1 g (58%
yield) of product as an oily solid. This solid was used without further purification in the

next step.

'11 NMR(CDC13): 5(ppm) 1.15 (t, 3H), 2.96 (q, 2H), 7.1-7.4 (m, 3H), 7.91 (d, 1H)

IR(CC14): 3400 (broad), 2976, 2876, 1695. 1576, 1530

2-Etlrylbenzyl alcohol

A solution of 2-ethylbenzoic acid (6.1 g, 0.041 moles) in 20 mL of anhydrous
ether was added dropwise over a period of 30 minutes to a stirred suspension of lithium
aluminum hydride (3.34 g, 0.088 moles) in 100 mL of anhydrous ether under an argon
atmosphere. The resulting mixture was stirred at room temperature for an hour and was
refluxed for 7 hours before being cooled to room temperature. The excess lithium

aluminum hydride was decomposed with careful addition of ice. Acidic workup afforded

134

5.1 grams (92% yield) of product as a yellow oil which was used without purification in

the next step.

lH NMR(CDC13): 8 1.25 (t, 3H), 2.72 (q, 2H), 2.12 (broad s, 1H), 4.73 (s, 2H), 7.2-7.4
(4H. m)

IR(CCl4): 3618, 3067.2, 2970.7, 2876.2, 1550.9,1253.8, 1217.2, 1062.9, 1003.1

2-Ethylbenzyl chloride

In a 250 mL round bottom flask was placed 5.1 grams (0.038 moles) of 2-
ethylbenzyl alcohol and 200 mL of concentrated hydrochloric acid. The mixture was
stirred at room temperature overnight. The mixture was then slowly added to 500 mL of
cold water and was extracted with two 50 mL portions of ether. The combined organic
layer was washed with water, saturated sodium bicarbonate and saturated sodium chloride
solutions and was dried over anhydrous magnesium sulfate. Solvent was evaporated to
yield 5.8 grams (100% yield) of product as a dark yellow oil which was used without

purification in the next step.

lH NMR(CDC13): 6 1.12 (t, 3H), 2.63 (q, 2H), 4.48 (s, 2H), 7.0-7.3 (m, 4H)

a—(Z-Ethylphenyl) acetonitrile

2.0 Grams (0.04 moles) of sodium cyanide was added to a flask containing 150
mL of dimethylsulfoxide. The mixture was heated to 80-90°C until all of the sodium
cyanide dissolved at which time a solution of 2-ethylbenzyl chloride (5.8 grams, 0.038
moles) in DMSO was added dropwise over a period of an hour. The mixture was heated

at 80-90°C for an additional 5 hours and then allowed to cool to room temperature. The

135

mixture was poured into a flask containing 500 mL of cold water. The aqueous layer was
washed with two 50 ml. portions of ether. The combined etheral layer was washed 10
times with water and dried over anhydrous magnesium sulfate. Solvent was evaporated to
afford 5.5 grams (100% yield) of a yellow oil which was used without purification in the

next step.

'11 NMR(CDC13): 5 1.23 (t, 3H), 2.68 (q, 2H), 3.71 (s, 2H), 7.2-7.4 (m, 4H)

IR(CC14): 2961.1, 2856.9, 2253, 1261.6, 1010.8

a—(2-EthylphenyD-fififl—tridcuteriopropionitrile

In a 100 mL round bottom flask equipped with a condenser and purged with argon
was placed 20 mL of dry THF along with 4.1 grams (0.041 moles) of diisopropyl amine.
The solution was cooled in an ice water bath. Butyl lithium (29 mL of 1.4 M solution)
was added dropwise to the mixture and it was allowed to stir at 0°C for an additional 30
minutes to ensure the complete formation of LDA. The mixture was then cooled to -78°C
in an acetone/dry ice bath while a solution of a—(2-ethylphenyl)acetonitrile (5.5 g, 0.038
moles) in THF was added dropwise. The solution turned dark-red in color. The solution
was allowed to warm to room temperature and stir for 2 hrs. before 2.5 mL of CD31 (5.8
g, 0.04 moles) was added. The mixture was stirred at room temperature for an hour and
was refluxed overnight. The solvent was removed to leave an oily residue which was
washed with ether/water mixture. The layers were separated and the water layer was
washed twice with ether. The combined organic layer was washed with water and dried

over anhydrous magnesium sulfate. Solvent was removed to yield 4.3 grams (70%) of a

136

brown oil. Kugelrohr distillation of the brown oil resulted in recovery of 4.1 g of product

as a colorless liquid.

'11 NMR(CDC13): 5 1.28 (t, 3H), 2.69 (q, 2H), 4.11 (broad s, 1H), 7.2-7.5 (m, 4H)

IR(CCl4): 3155.9, 2985.2, 2902.3, 2254.1, 1470.9, 1383.2, 1096.7

a—(2-Ethylphcnyl)-fi,,B,,B—trideuteriopropiophenone

A solution of a-(2-ethylphenyl)-B,B,B—tridueteropropionitrile (4.1 g, 0.025
moles) in 30 mL of anhydrous ether was added dropwise over a period of 30 minutes to a
stirred solution of phenyl magnesium bromide (prepared from 5.18 g (0.033 moles) of
bromobenzene and 0.8 g (0.033 moles) of magnesium in 50 mL of anhydrous ether).
After the addition was complete, the mixture was refluxed for 10 hours and allowed to
cool to room temperature. The mixture was then added to 100 mL of 10% HCl and layers
were separated. The aqueous layer was placed in a round bottom flask and was heated at
90°C overnight. The mixture was allowed to cool to room temperature, ether was added
and layers were separated. The aqueous layer was washed twice with ether and the
combined organic layer was washed with water, saturated sodium bicarbonate, and
saturated sodium chloride solutions. The organic layer was then dried over anhydrous
magnesium sulfate. Solvent removal resulted in a yellow oil which after chromatography
(by flash chromatography using 97:3 hexane/ethylacetate solution as eluent) afforded 2.9
grams (48% yield, 0.012 moles) of pale-yellow oil which crystallized upon cooling in the

refrigerator.

137

'11 NMR(CDC13): 5 1.32 (t, J= 7.5112, 3H, CH3), 2.84 (AB quartet of q, 1= 7.6, 4.5Hz,
2H, CH2), 4.78 (broad s, 1H, CHCD3), 7.04 (dt, 1: 7.8 Hz, I: 1.71 Hz, 2H, Ar), 7.15 (dd,
1: 67,171 Hz, 1H, Ar), 7.20 (broad d, 111, Ar), 7.32 (dd, 1: 7.14 Hz, 1: 7.62 Hz, 2H,
Ar), 7.41 (t, 1: 7.6 Hz, 1H, Ar), 7.82 (d, J: 7.11 Hz, 211, Ar)

211 NMR(CDC13): 5 1.18 (5, 3D)

13(: NMR(CDC13): 5 15.11, 18.15 (septet, CD3), 25.46, 43.76, 126.49, 126.99, 127.17,
128.38, 128.46,128.96, 132.53, 136.72, 139.30, 140.37.201.15

IR(CC14) : 3067, 3026, 2967, 2928, 2876,2233, 1686, 1217, 1006

m.p.: 36-38°C

HRMS: 241.15429 calculated for C17H15D30; found: 241.1547

01—(2-Ethylphenyl)propiophenone (4)

a-(2-Ethylphenyl)propiophenone was synthesized using the same procedure as 01-
(2-ethylphenyl)-B,B,B-trideuteropropiophenone with the exception of using methyl iodide
instead of CD31.
lH NMR(CDC13): 5 1.32 (t, J= 7.5Hz, 3H, CH3), 1.49 (d, J=6.8 Hz, 3H, CH3CH), 2.84
(AB quartet of q, I: 7.6, 4.5Hz, 2H, CH2), 4.78 (q, J= 6.8 Hz, 1H, CHCH3), 7.04 (dt, J=
7.8 Hz, J= 1.71 Hz, 2H, Ar), 7.15 (dd, J= 6.7,1.71 Hz, 1H, Ar), 7.20 (broad d, 1H, Ar),
7.32 (dd, J= 7.14 Hz, J= 7.62 Hz, 2H, Ar), 7.41 (t, J= 7.6 Hz, 1H, Ar), 7.82 (d, J= 7.11
Hz, 2H, Ar)
l3C NMR(CDC13): 8 15.11, 18.15, 25.46, 43.76, 126.49, 126.99, 127.17, 128.38, 128.46,

128.96, 132.53, 136.72, 139.30, 140.37, 201.15

138

IR(CCl4) : 3067, 3026, 2967, 2928, 2876, 1686,. 1217, 1006

m.p.: 36-38°C

a-(2-Ethylphenyl)acetone (10)
a-(2-Ethylphenyl)acetone was prepared by the reaction of methyl lithium and 01—

(2-ethylphenyl)acetic acid following the route given below:

/

 

 

OJ
1
.9
\/

/

0021-1 CHZOH CHZCI
mm, 0 HCl or
soon2

NaCN
DMSO

CH3 1.2Eq.CH3Li OH HCI.A \ 0“ch

 

 

2. H’

O /
3

/
O

/
Q

Scheme 52. Synthesis of a-(2-Ethylphenyl)acetone

a—(Z-Ethylphenybacetic acid

In a 250 mL round bottom flask equipped with a condenser was placed 5.0 g
(0.035 moles) of 01—(2-ethylphenyl)acetonitrile along with 200 mL of concentrated
hydrochloric acid. The mixture was refluxed for 48 hours, allowed to cool to room
temperature and was poured slowly into a flask containing 500 mL of ice cold water. The

aqueous layer was extracted with ether several times and the combined ether layer was

washed twice with 5% NaOH solution. The alkaline layer was acidified with 10% HCl

139

solution until a white precipitate could be observed. The precipitate dissolved upon ether
extraction and the organic layer was washed with water and saturated sodium chloride
solutions and dried over anhydrous magnesium sulfate. Solvent was evaporated to leave
3.5 g (60% yield, 0.021 moles) of product as white powder which was used without
purification in the next step.

1111 NMR(CDC13): 5 1.2 (t, 3H), 2.65 (q, 2H), 3.68 (s, 2H), 7.1-7.2 (m, 4H)

IR(CC14): 3350, 2960, 1686, 1456.4, 1201.8, 1057.2

a—(2-Ethylphenyl)acetone

To a solution of a-(2-ethylphenyl)acetic acid (3.5 g, 0.021 moles) in 50 mL
anhydrous ether at 0°C under an argon atmosphere, was added 36 mL of 1.4 M methyl
lithium. The mixture was allowed to warm to room temperature and was stirred
overnight. The mixture was then poured into a flask containing 30 mL of 10% HCl and
was stirred for 30 minutes before layers were separated. The aqueous layer was washed
with ether twice and the combined organic layer was washed with water and saturated
sodium chloride solution and dried over anhydrous magnesium sulfate. Solvent was

removed to yield 2.7 g (80%) of product as a pale yellow oil.

lH NMR(CDC13): 5 1.17 (t, 7.56 Hz, 3H, CH3), 2.13 (s, 3H), 2.56 (q, 7.53 Hz, 2H, CH2),
3.71 (s, 2H), 7.1-7.3 (m, 4H)

l3CNMR(CDCI3): 6 14.79, 25.78, 29.26, 48.59, 126.18, 127.60, 128.67, 130.63, 132.4,

142.62, 206.75

IR(CC14): 3069, 3022, 2970, 2936, 2876, 1707, 1358, 1159, 1057

140

HRMS: 162.10446 calculated for C, ,H,4O; found: 162.1080

a—Mesitylacetone (11)

a-Mesitylacetone was prepared by the reaction of methyllithium with 01—

mesitylacetic acid following the route described below:

mH Cl CHZCN
I: 2 NaCN \ HCl A 1 CHgLiZHZEq.
DMSO

Scheme 53. Synthesis of a-Mesitylacetone

a—Mesiqlacetonitrile

A mixture of sodium cyanide (8.7 g, 0.19 moles) in DMSO was heated at 90°C
until all of the sodium cyanide dissolved. 01—2,4,6-Trimethylbenzyl chloride (20 g, 0.12
moles) was added dropwise over a period of an hour and the mixture was heated for an
additional 5 hours. The mixture was then allowed to cool to room temperature and was
poured into 500 mL of ice—cold water. The resulting solution was extracted with ether
three times and the combined ether layer was washed with water and dried. Solvent was
evaporated to leave the desired product (18 g, 92%) as a yellow solid. The crude product

was used without further purification.
'11 NMR(CDC13): 5 2.30 (s, 311), 2.38 (s, 6H), 3.60 (s, 211), 6.93 (s, 211)

IR(CC14): 2921, 2240, 1404.4

141

a—Mesitylacetic acid

a-Mesitylacetonitrile (18 g, 0.11 moles) was poured into 300 mL of concentrated
HCl and the mixture was refluxed for two days. The mixture was then allowed to cool to
room temperature and was poured into 1 L of water. The resulting solution was extracted
with ether several times. The ether layers were combined and washed with 10% NaOH
solution. The alkaline layer was acidified and extracted with ether twice. The combined
ether layer was washed with water and dried. Solvent was evaporated, giving the product
as a white solid (15.3 g, 76%). This was used without further purification.
lH NMR(CDC13): 8 2.3 (s, 3H), 2.41 (s, 6H), 3.50 (s, 2H), 6.95 (s, 2H)

IR(CC14): 3383, 2921.8, 1686, 1458.4, 1325.3, 1228.8, 1188.3, 852.6

a—Mesitylacetone

To a solution of a—mesitylacetic acid (5 g, 0.027 moles) in 50 mL anhydrous
ether at 0°C under an argon atmosphere, was added 40 mL of 1.4M methyl lithium. The
mixture was allowed to warm to room temperature and was stirred overnight. The
mixture was then poured into a flask containing 30 mL of 10% HCl and was stirred for 30
minutes before layers were separated. The aqueous layer was washed with ether twice and
the combined organic layer was washed with water and saturated sodium chloride
solution and dried over anhydrous magnesium sulfate. Solvent was removed to yield 3.4

g (72%) of product as an off-white solid. The product was recrystallized from methanol.
lH NMR(CDC13): 8 2.12 (s, 3H), 2.19 (s, 6H), 2.25 (s, 3H), 3.71 (s, 2H), 6.86 (s, 2H)

l3CNMR(CDCI3): 5 20.2, 20.9, 29.3, 44.8, 128.9, 129.1, 136.5, 136.6, 206.7

142

IR(CC14): 2920.6, 1711.1, 1417.8, 1167.1
m.p.: 60-62°C

HRMS: 176.12012 calculated for C,2H,6O; found: 176.1203

01'(2-Benzylphenyl)propiophenone (7)
01—(2-Benzylphenyl)propiophenone was prepared by the reaction of phenyl

magnesium bromide with 01—(2-benzylphenyl)propionitrile following the route described

 

 

below.
ph Ph Ph
\ COzH LiAIH. 0“on HCl or 9:1/CHM NaCN ”1&0“?
/ SOC12 I / DMSO
1. LDA
2.011,:
0 Ph
'\ 1.PhLi or PhMgBr / on
O 2. H". A \
Scheme 54. Synthesis of a-(Z-Benzylphenyl)propiophenone
o-Benzylbenzyl alcohol

A solution of o-benzylbenzoic acid (0.033 moles,7 g, Aldrich) in 15 mL of
anhydrous ether was added dropwise to an argon purged stirred suspension of lithium
aluminum hydride (2.7 g, 0.071 moles) in 50 mL of anhydrous ether. After addition
was complete, the mixture was refluxed for 7 hours and allowed to cool to room

temperature. Excess lithium aluminum hydride was quenched by careful addition of ice.

143

Acidic workup afforded 5.5 g (84% yield) of product as a yellow oil which was used in

the next step without purification.

'11 NMR(CDCl3): 5 4.10 (s, 2H), 4.68 (s, 2H), 7.1-7.5 (m, 9H)

o-Benzylbenzyl chloride

In a 250 mL round bottom flask was placed 5.5 g of o-benzylbenzyl alcohol along
with 200 mL of concentrated hydrochloric acid. The mixture was stirred at room
temperature overnight and was poured slowly into a flask containing 500 mL of ice cold
water. Ether was added and layers were separated. The aqueous layer was washed twice
with ether and the combined organic layer was washed with water, saturated sodium
bicarbonate and saturated sodium chloride solutions and was dried over anhydrous
magnesium sulfate. Removal of solvent resulted in recovery of 5.85 g (100% yield) of

product as a yellow oil. This was used without purification in the next step.

lH NMR(CDC13): 8 4.19 (s, 2H), 4.58 (s, 2H), 7.1-7.4 (m, 9H)

a—(2-Benzylphenyl)acetonitrile

A solution of (2-benzyl)benzyl chloride (5.85 g, 0.027 moles) in 10 mL of DMSO
was added dropwise to a stirred solution of sodium cyanide (1.8 g, 0.036 moles) in 100
mL of DMSO. The mixture was refluxed overnight , allowed to cool to room temperature
and was poured into a flask containing 500 mL of ice cold water. Ether was added and
layers were separated. The aqueous layer was washed twice with ether and the combined

organic layer was washed 10 times with water and dried over anhydrous magnesium

144

sulfate. Solvent removal afforded 5.1 g (91% yield) of product as a brownish oil which

was used without purification in the next step.

lH NMR(CDC13): 8 3.35 (s, 2H), 4.01 (s, 2H), 7.0-7.4 (m, 9H)

a—(Z-Benzylphenyl)propiophenone

A solution of a—(2-benzylphenyl)propionitrile (2.5 g, 0.011 moles) in anhydrous
ether was added dropwise to a stirred solution of phenyl magnesium bromide (prepared
from 2.0 g, 0.013 moles of bromobenzene and 0.32 g of magnesium) in 50 mL of ether.
The mixture was refluxed overnight and cooled to room temperature before it was poured
into a flask containing 100 mL of 10% HCl. Layers were separated and the aqueous layer
was heated at 80-90°C for 7 hours. Ether was added and the layers were separated. The
aqueous layer was washed twice with ether and the combined organic layer was washed
with water and saturated sodium chloride and dried. Solvent removal yielded 1.8 g (54%)
of crude product as a dark yellow oil. The oil was chromatographed (by flash
chromatography using 95/5 hexane/ethyl acetate mixture as eluent) to yield 1.3 g of pure

product as a pale yellow oil.

111 NMR(CDC13): 5 1.36 (d, 6.7 Hz, 3H, CH3), 4.16 (s, 2H), 4.73 (q, 6.7 Hz, 1H.
CHCH3), 7.02 (dd, 1: 7.62, 1.59 Hz, 1H, Ar), 7.1-7.4 (m, 11H, Ar), 7.46 (d, I: 7.14 Hz,
2H, Ar)

13CNMR(CDC13): 5 18.54, 39.50, 43.93, 126.37, 126.90, 127.39, 127.57, 128.24, 128.42,
128.63, 128.90, 131.59, 132.41, 136.34, 137.13, 140.01, 140.19, 200.93

IR(CC14): 3067, 3028, 2964, 2932, 1688, 1452, 1261, 1022

145

HRMS: 300.15142 calculated for C22H200; found: 300.1521

or—(2,4,6-Triethylphenyl)-0,0,B-tridueteropropiophenone (5d3)
01—(2,4,6-Triethylphenyl)-B,B,B-tridueteropropiophenone was prepared by
reaction of phenyl magnesium bromide with 01—(2,4,6-triethylphenyl)B,B,B-

tridueteropropionitrile according to the route outlined below.

CHZCN
\ HCHO CHZC' NaCN O 1. LDA ON
I / . HCl. A DMSO 2. C03|

1. PhLi or PhMgBr

2. 11*, A
\

/ 0

Scheme 55. Synthesis of 01-(2,4,6-Triethylphenyl)-B,B,B-trideuteropropiophenone

2,4,6-Triethylbenzyl chloride

In a 250 mL round bottom flask was placed 10.0 g (0.062 moles) of 1,3,5-
triethylbenzene along with 2.0 g (0.066 moles, Aldrich) of paraforrnaldehyde and 200 mL
of concentrated hydrochloric acid. The mixture was refluxed for 48 hours, allowed to cool
to room temperature and was poured into a flask containing 500 mL of 20% NaOH

solution. The mixture was stirred at room temperature for an hour. Ether was added and

146

layers were separated. The aqueous layer was washed twice with ether and the combined
organic layer was washed with water, dilute alkali and saturated sodium chloride
solutions and dried. Solvent was removed to yield a reddish-brown oil which upon
analysis was shown to contain both starting material and the desired product. Kugelrohr
distillation of this oil resulted in recovery of 11.6 g (89% yield) of a yellow oil as pure

product.

lH NMR(CDC13): 5 1.22 (t, 311), 1.26 (t, 6H), 2.60 (q, 211), 2.75 (q, 4H), 4.70 (s, 2H),

6.90 (s, 2H)

a—(Z, 4, 6-Triethylph enyl)aceton itrile

A solution of 2,4,6-t1iethylbenzylchloride (11.6. g, 0.055 moles) in 10 mL of
DMSO was added dropwise to a stirred solution of sodium cyanide (0.06 moles in 100
mL DMSO) at 80°C. The mixture was heated at 80-100°C overnight, allowed to cool to
room temperature and was poured into a flask containing 500 mL of ice cold water. Ether
was added and the layers were separated. The aqueous 1ayer was washed twice with ether
and the combined organic layer was washed 10 times with water and dried (MgSO4).
Solvent was removed to afford 7.02 g (63.5% yield, 0.035 moles) of an off-white solid as

product which was used in the next step without further purification.

lH NMR(CDC13): 8 1.2 (t, 3H), 1.25 (t, 6H), 2.6 (q, 2H), 2.68 (q, 4H), 3.62 (s, 2H), 6.9
(s, 2H)

IR(CC14): 2961.1, 2235.8, 1608.8, 1456.4, 1251.9, 873.8

147

a—(2,4,6-Triethylphenyl)-,6,,B,fl—tridueteropropionitrile

In a 250 mL round bottom flask equipped with a condenser and purged with argon
was placed 4.00 g (0.04 moles) of diisopropylamine in 30 mL of dry THF. The solution
was cooled to 0°C in an ice-water bath. Butyl lithium (28 mL of 1.4 M solution) was
added and the mixture was allowed to warm to room temperature and stirred for half an
hour. The mixture was then cooled to -78°C in an acetone/dry ice bath and 7.02 g (0.035
moles) of 01—(2,4,6-triethylphenyl) acetonitrile in 20 mL of dry THF was added dropwise.
After addition was complete, the mixture was allowed to warm to room temperate and

was stirred for 4 hours before 2.6 mL (5.8 g, 0.04 moles) of CD31 was added. The

mixture was stirred at room temperature for an hour and refluxed overnight. After
cooling to room temperature, solvent was evaporated to yield a pale yellow oil which was
washed with an ether/water mixture. Layers were separated and the water layer was
washed three times with ether. The combined organic layer was washed with water and
saturated sodium chloride and dried. Removal of solvent resulted in recovery of 4.36 g
(57% yield, 0.02 moles) of product as a crystalline solid. This was used in the next step

without purification.

lH NMR(CDC13): 5 1.20 (t, 3H), 1.25 (t, 6H), 2.60 (q, 2H), 2.75 (AB quartets of q, 4H),

4.23 (broad s, 1H), 6.92 (broad s, 2H)

a—(2,4,6- T rieth ylphen yl-fl, ,B, ,B—tridueteropropiophenone

A solution of a—(2,4,6-triethylphenyl)-B,B,B-tridueteropropionitrile (4.36 g, 0.02

moles) in 20 mL of anhydrous ether was added dropwise to a stirred solution of phenyl

148

magnesium bromide (prepared from 3.6 g (0.022 moles) of bromobenzene and 0.95 g
(0.022 moles) of dry magnesium) in 100 mL of anhydrous ether. The mixture was
refluxed overnight, cooled to room temperature and poured into a flask containing 100
mL of 10% HCl solution. Layers were separated and the aqueous layer was heated at 80-
90°C, for four hours. After cooling to room temperature, ether was added and the layers
were separated. The aqueous layer was washed twice with ether and the combined
organic layer was washed with water, saturated sodium bicarbonate and saturated sodium
chloride and dried. Solvent removal resulted in recovery of 3.2 g (54% yield) of product

as an off-white powder.

lH NMR(CDC13): 5 1.15 (broad, 6H, 2CH,), 1.19 (t, J= 7.5 Hz, 3H, CH3), 2.55 (q, J= 7.5
Hz, 211, CH2), 2.6 (broad, 4H, 2CH2), 4.48 (broad s, 1H, CHCD3), 6.86 (broad s, 2H, Ar),
7.23 (dd, J: 7.3, 7.6 Hz, 2H, Ar), 7.36 (t, J: 7.3Hz, 1H, Ar), 7.67 (d, J= 7.6Hz, 2H, Ar)
2H NMR(CDC13): 5 1.18 (s, 3D)

l3C NMR(CDC13): 5 15.20, 17.2 (septet, CD3), 28.4, 29.65, 29.69, 45.41, 126.74, 128.11,
128.57, 132.23,135.76, 137.10, 141.4, 142.58, 202.89

IR(CCl4): 2978, 2936,2866, 1684, 1383, 1217, 1006 cm -1

m.p.: 75-76°C

HRMS: 297.21689 calculated for C2,H23D3O; found: 297.2168

149

I
300
3009'
fir/‘7‘
3°09-

, “PF:
3081
I

a“
I
WI

5
"If
I
fiIr”

 

 

 

 

(4714,71

SLII
TI
0'

 

 

Figure 33. Variable Temperature NMR of 01-(2,4,6-Triethylphenyl)-B,B,B-
trideuterio-propiophenone in Acetone- d6

150

01—(2,4,6-Triethylphenyl)propiophenone (5)

01—(2,4,6-Triethylphenyl)propiophenone was synthesized using the same
procedure as 01-(2,4,6—triethylphenyl)-B,B,B-trideuteriopropiophenone with the exception
of using CH3I instead of CD31.
lH NMR(CDC13): 8 1.15 (broad, 6H, 2CH3), 1.19 (t, J= 7.5 Hz, 3H, CH3), 1.55 (d, J= 6.8
Hz, 3H, CH3CH), 2.55 (q, J= 7.5 Hz, 2H, CH2), 2.6 (broad, 4H, 2CH2), 4.48 (q, I: 6.8
Hz, 1H, CHCH3), 6.86 (broad s, 2H, Ar), 7.23 (dd, J= 7.3, 7.6 Hz, 2H, Ar), 7.36 (t, J=
7.3Hz, 1H, Ar), 7.67 (d, I: 7.6Hz, 2H, Ar)
l3C NMR(CDC13): 8 15.20, 17.2, 28.4, 29.65, 29.69, 45.41, 126.74, 128.11, 128.57,
132.23, 135.76, 137.10, 141.4, 142.58, 202.
1R(CC14): 2978, 2936, 2866, 1684, 1383, 1217, 1006 cm '1

m.p.: 75-76°C

a—(2,4,6-Triethylphenyl)acetone (12)
01—(2,4,6-Triethylphenyl)acetone was synthesized by reaction of methyl lithium

with 01—(2,4,6-triethylphenyl)acetic acid according to the route described below:

 

CH3
1. 2Eq. c1131
2. 11* 0

Scheme 56. Synthesis of 01-(2,4,6-Triethylphenyl)acetone

 

151

err—(2,4,6-Triethylphenyl)acetic acid

A solution of ct—(2,4,6-triethylphenyl)acetonitri1e (3.0 g, 0.015 moles) in
concentrated hydrochloric acid was refluxed for two days. After cooling to room
temperature, the solution was poured onto cold water and extracted with ether several
times. The combined ether layer was washed twice with 1N NaOH solution. The alkaline
layer was acidified with 10% hydrochloric acid until a white precipitate was formed. The
precipitate was extracted into ether, washed twice with water and dried. Solvent removal
afforded 3.2 g (100% yield) of product as a white solid. This was used in the next step

without further purification.

1H NMR(CDC13): 8 1.18 (t, 6H), 1.21 (t, 3H), 2.58 (q, 2H), 2.61 (q, 4H), 3.72 (s, 2H),
6.9 (s, 2H)

IR(CC14): 3354.6, 2961, 1686, 1251.9, 1057.2, 1014.7

car—(2,4, 6— T rieth ylph en yl)acetone

Methyl lithium (14 mL of 1.4 M solution) was added dropwise to a stirred
solution of 01—(2,4,6-triethylphenyl)acetic acid (1.8 g, 0.008 moles) in 100 mL of
anhydrous ether at 0°C. The mixture was warmed to room temperature, refluxed for 48
hours, and poured into' a flask containing 100 mL of 10% HCl solution. Layers were
separated and the aqueous layer was washed twice with ether. The combined organic
layer was washed with water, dilute alkali and water and dried. Solvent removal afforded

a yellow oil which was chromatographed (by flash chromatography using 99:1

152

hexane/ethyl acetate mixture as eluent) to give 1.6 g (73% yield) of product as a pale

yellow oil.

'H NMR(CDC13): 5 1.18 (t, 1=7.5 Hz, 6H, 2011,), 1.23 (t, J=7.5 Hz, 311, CH3CO), 2.16
(s, 3H, CH3), 2.53 (q, 1=7.5 Hz, 4H, 2CH2 CH3), 2.60 (q, 1=7.5 Hz, 2H, CH2CH3). 3.78
(s, 211, (311,130), 6.92 (s, 2H, Ar)

l3c: NMR(CDC13): 5 15.05. 15.40, 26.56, 28.58, 29.40, 43.74, 125.90, 127.76, 142.66,
143.12, 207.40

IR(neat): 2965,2932, 2874, 1716.9, 1458.4, 1157.4

HRMS: 218.16706 calculated for C ,SHZZO; found: 218.1664

a—(2,4,6-Triisopropylphenyl)acetone (13)

01-(2,4,6-Triisopropylphenyl) acetone was synthesized by reaction of methyl
lithium with a—(2,4,6-triisopropylphenyl)acetic acid according to the route outlined

below.

   
 

\ “CH0 I \ CHZC' NaCN I \ CHZCN HCI,A / OH
I] / HCI,A fi/I / omsoj) \ o
1.2EQ.CH3L1
2. H+
/ 0

Scheme 57. Synthesis of 01-(2,4,6-Triisopropylphenyl)acetone

153

2,4,6-Triisopropylbenzyl chloride

In a 250 mL round bottom flask was placed 10 g (0.049 moles, Aldrich) of
triisopropylbenzene along with 1.56 g (0.052 moles) of paraforrnaldehyde and 200 mL of
concentrated hydrochloric acid. The mixture was refluxed for three days, cooled to room
temperature and was poured into a flask containing 500 mL of 20% NaOH solution. The
mixture was stirred at room temperature for two hours before ether was added. Layers
were separated and the aqueous layer was washed twice with ether. The combined
organic layer was washed with water, dilute alkali and water and dried. Removal of
solvent resulted in recovery of a yellow oil. Analysis of the oil showed it to contain both
the starting material and the desired product. Kugelrohr distillation resulted in recovery of

3.8 g (30% yield) of the product as a yellow oil.
lH NMR(CDC13): 8 1.22 (d, 3H), 1.26 (d, 6H), 2.85 (septet, 1H), 3.28 (septet, 2H), 4.71

(s, 2H), 7.0 (s, 2H)

a—(2,4, 6- T riisopropylphen yl) acetonitrile

A solution of 2,4,6-triisopropylbenzyl chloride (3.8 g, 0.015 moles) in 10 mL of
DMSO was added dropwise to a stirred solution of sodium cyanide (0.9 g, 0.018 moles)
in 50 mL DMSO at 90°C. The mixture was stirred overnight, cooled to RT and was
poured into a flask containing 500 mL of water. Ether was added and layers were
separated. The aqueous layer was washed twice with ether and the combined organic
layer was washed 10 times with water and dried. Solvent removal afforded 3.6 g (100%

yield) of product as a yellow solid.

154

'11 NMR(CDC13): 5 1.22 (d, 3H). 1.27 (d, 6H), 2.85 (septet, 1H), 3.13 (septet, 2H), 3.71

(s, 2H), 7.02 (s, 2H)

IR(CC14): 2966, 2238.2, 1456.5, 727.3

a—(2,4,6-TriisopropylphenyDacetic acid

A stirred mixture of 01—(2,4,6-triisopropylphenyl)acetonitrile (3.6 g, 0.015 moles)
in 200 mL of concentrated hydrochloric acid was refluxed for 48 hours. The mixture was
allowed to cool to room temperature and was poured slowly into a flask containing 500
mL of ice cold water. Ether was added, layers were separated and the organic layer was
washed with dilute NaOH solution. The alkaline layer was acidified with 10% HCl
solution until a white precipitate could be observed. Ether was added and layers were
- separated. The organic layer was washed twice with water and dried. Solvent removal

afforded 1.2 g (30% yield) of product as a white solid.

'11 NMR(CDC13): 5 1.21 (t, 6H), 1.23 (t, 3H), 2.87 (septet, 1H), 3.10 (septet, 2H), 3.80 (s,
2H), 7.0 (s, 2H)

IR(CC14): 3350.6, 2966, 1687, 1058.1

a—(2,4,6- T riisopropylph en yl)acetone

Methyl lithium (6.8 mL of 1.4 M solution) was added dropwise to a stirred
solution of a—(2,4,6-triisopropylphenyl)acetic acid (1.2 g, 0.0045 moles) in 100 mL of
anhydrous ether at 0°C. The mixture was warmed to room temperature, refluxed
overnight, and poured into a flask containing 100 mL of 10% HCl solution. Layers were

separated and the aqueous layer was washed twice with ether. The combined organic

155

layer was washed with water, dilute alkali and water and dried. Solvent removal afforded
a yellow oil which was chromatographed (by flash chromatography using 99:1
hexane/ethyl acetate mixture as eluent) to give 0.35 g (30% yield) of product as a white
solid.

1H NMR(CDC13): 8 1.19 (t, J=6.8 Hz, 12H, 4CH3), 1.23 (t, J=6.9 Hz, 6H, 2CH3), 2.18 (s,
3H, CH3CO), 2.85 (septet, J=6.8 Hz, 1H, CH(CH3)2), 2.90 (septet, J=6.8 Hz, 2H,
2CH(CH3)2), 3.84 (s, 2H, CHzCO), 7.00 (s, 2H, Ar)

13C NMR(CDC13): 8 23.98, 29.48, 29.73, 30.05, 34.15, 43.17, 121.11, 121.16, 146.96,
147.58, 207.8

IR(neat): 2959.2, 2928.3, 2870.4, 1711.1, 1360, 1159.4

m.p.: 57-59°C

HRMS: 260.21402 calculated for C,8H280; found: 260.2141

(rt—(2,4,6-Triisopropylphenyl)acetophenone (9)

01—(2,4,6-Triisopropylphenyl)acetophenone was synthesized by reaction of phenyl
magnesium bromide with 01-(2,4,6-triisopropylphenyl)acetonitrile according to the route

outlined below:

 

CHZCN
O 1. PhLi or PhMgBr
2. H”, A

Scheme 58. Synthesis of 00-(2,4,6-Triisopropylphenyl)acetophenone

 

156

a-(2,4,6—Triisopropylphenyl)acetophenone

A solution of 01—(2,4,6-triisopropylphenyl)acetonitrile (0.012 moles, 3.0 g) in
anhydrous ether was added dropwise to a stirred solution of phenyl magnesium bromide
(prepared from 2.2 g of bromobenzene and 0.35 g of magnesium) in anhydrous ether.
The mixture was stirred at room temperature for an hour and refluxed overnight. After
cooling to room temperature, 50 mL of 10% hydrochloric acid solution was added and
layers were separated. The aqueous layer was heated at 90°C for four hours and cooled to
room temperature. Ether was added and layers were separated. The organic layer was
washed with water, saturated sodium bicarbonate and saturated sodium chloride solutions
and dried. Solvent was evaporated to leave a yellow oil which was chromatographed (by
flash chromatography using 95:5 hexane/ethyl acetate mixture as eluent) to leave 2.3 g

(60% yield) of product as a white solid.

'H NMR(CDC13): 5 1.18 (d, J=6.8 Hz, 12H, 4CH3), 1.26 (d, J=6.8 Hz, 6H, 2C11,), 2.85
(septet, J=6.8 Hz, 2H, 2CH(CH3)2), 2.89 (septet, J=6.8 Hz, 1H, CH(CH3)2), 4.45 (s, 211,
CH2CO), 7.04 (s, 2H, Ar), 7.51 (dd, 1:7.35. 7.2 Hz, 211, Ar), 7.61 (tt, 1:72, 1.35 Hz,
1H, Ar), 8.08 (dd, 1:735, 1.35 Hz, 2H, Ar)

”C NMR(CDC13): 5 24.03, 24.08, 30.30, 34.24, 37.67, 121.0, 126.54, 128.09, 128.73,

133.13, 137.12, 147.12, 147.42, 197.75

IR (CG): 2965, 1691, 1448, 1216

HRMS: 322.22966 calculated for C23H3OO; found: 322.2307

mp: 107—109°C

157

o—tert-Butyl-a,a,a-trifluroacetophenone (l4)

o-rert-Butyl-a,01,a-trifluroacetophenone was synthesized by reaction of o-tert-

butyl phenyllithium with ethyl trifluroacetate according to the route outlined below:

\
\
I H1193 IQ Br: 1. HCl
/ H2804 ‘ / H2804 P10: NaNOZ
AgZSO4 2 H3P02

1. BuLi
2. CF3COOE1

 

 

/ o

I die"

/.

Scheme 59. Synthesis of o-tert-Butyltrifluroacetophenone

4-tert-Butyl nitrobenzene

A solution of nitric acid (2.5 mL of 15.5 M solution) in 15 mL of concentrated
sulfuric acid was added dropwise to 5 g (0.037 moles, Aldrich) of tert-butylbenzene at
0°C. After the addition was complete, the mixture was stirred at 0°C for an hour, warmed
to room temperature and poured into a separatory funnel. Layers were separated and the
organic layer was washed with water twice and dried. The resulting yellow oil was
distilled through a fractionating column to separate the para isomer. The desired product

(5.7 g, 85% yield) was obtained as a pale yellow oil.

'H NMR(CDC13): 5 1.32 (s, 9H), 7.5 (d, 2H), 8.14 (d, 2H)

, 158

3-Bromo-4—tert-bu0zlnitr0benzene

In a 500 mL three necked round bottom flask was placed 5.7 g (0.032 moles) of 4-
tert-butylnitrobenzene, silver sulfate (10 g, 0.032 moles), and 300 mL of concentrated
hydrochloric acid. The mixture was stirred for 0.5 hours before 1.7 mL (0.032 moles) of
bromine was added dropwise over a period of an hour. The mixture was allowed to stir at
room temperature for an additional five hours and then poured into 1 liter of dilute
sodium sulfite solution. The silver bromide was collected by suction filtration. The
filtrate was extracted three times with ether and the combined ether layer was washed
with water, 10% NaOH, water and dried over anhydrous magnesium sulfate. Solvent
removal afforded 7.2 g (87%, 0.028 moles) of product as a yellow oil. This was used in

the next step without further purification.

lH NMR(CDC13): 5 1.51 (s, 9H), 7.6 (d, 1H), 8.05 (dd, 1H), 8.4 (d, 1H)

3-Bromo-4-tert-bugrlanilinium chloride

3-Bromo-4-tert-butylnitrobenzene (7.2 g, 0.028 moles) was reduced in a Parr
hydrogenator in the presence of 0.15 g platinum(IV) oxide (Aldrich, Adam's catalyst) in a
mixture containing 100 mL of 95% ethanol and 15 mL of concentrated hydrochloric acid
at a pressure of 47-50 psi of hydrogen at room temperature. The hydrogenation took
approximately 18 hours. The reaction mixture was filtered through a celite pad to remove
the catalyst. Solvent removal afforded 7.3 g (100% yield, 0.028 moles) of amine

hydrochloride as a yellow solid.

1H NMR(CDC13): 8 1.5 (s, 9H), 7.48 (dd, 1H), 7.71 (d, 1H), 7.81 (d, 1H)

159

2-tert-Butylbromobenzene

In a 250 mL round bottom flask was placed 7.3 g (0.028 moles) of 3-bromo-4-
tert-butylanilinium chloride and 30 mL of concentrated hydrochloric acid. The mixture
was diluted with water to 100 mL and ice chips were added to cool the mixture to 0°C. A
solution of sodium nitrite (2.0 g, 0.030 moles) in 10 mL of water was added to the
mixture over a period of two minutes. The mixture was stirred at 0°C for an additional 15
minutes before it was vacuum filtered to give a clear yellow solution which was kept at
0°C. A 50% solution of hypophosphorous acid (70 mL) was added to the filtrate and the
mixture was kept in the freezer for 48 hours. The mixture was then allowed to warm to
room temperature and was extracted with ether three times. The combined ether layer was
washed with water and dried over anhydrous magnesium sulfate. Solvent was evaporated
to give a brownish oil which upon Kugelrohr distillation yielded 3.6 g (62% yield, 0.017

moles) of product as a colorless liquid.

'H NMR(CDCI3): 5 1.5 (s, 9H), 7.01 (ddd, 1H), 7.22 (ddd, 1H), 7.43 (dd, 1H), 7.57 (dd,

1H)

2-tert-B utyl- a, a, a-trifluroacetoph en one

To a stirred solution of 2-tert-butylbromobenzene (3.6 g, 0.017 moles) in 50 mL
of anhydrous ether at -78°C, was added 11 mL of 2.0 M n-butyllithium (0.022 moles).
The solution was allowed to warm to 0°C and was stirred at this temperature for 4 hours
before 3.1 g (0.022 moles) of ethyl trifluoroacetate in 10 mL of anhydrous ether was

added. The mixture was allowed to warm to room temperature and was refluxed

160

overnight. After cooling to room temperature, the mixture was poured onto 150 mL of
saturated ammonitun chloride solution and layers were separated. The organic layer was
washed twice with saturated sodium chloride solution and dried. Solvent was evaporated
to leave a brownish oil which was chromatographed (by flash chromatography using
90:10 hexane/ethyl acetate mixture as eluent) to afford 2.76 g (72% yield) of product as a
colorless oil. .

lH NMR(CDC13): 5 1.37 (s, 9H, C(CH3)3), 7.28 (dd, J= 6.81, 1.10 Hz, 1H, Ar), 7.30
(broad, 1H, Ar), 7.46 (ddd, J= 8.2, 6.81, 1.85 Hz, 1H, Ar), 7.57 (dd, J: 8.2, 1.1 Hz, 1H,
Ar)

l3C NMR(CDC13): 5 32.0, 36.0, 116 (q, J= 291.4 Hz), 125.3, 126.3, 127.9, 131.33, 132.6,
149.9, 189 (q, J: 35.2 Hz)

19F NMR(CDC13): 5 1.83 (s, 3F, CF 3) reference: ethyl trifluroacetate

IR(CC14): 2968.8, 1741.9, 1207.5, 1182.5, 1155.5

HRMS: 230.09185 calculated for C12H13OF3; found: 230.0919

o-(2,3-Dimethyl-2-butyl)benzophenone (15)
0-(2,3-Dimethyl-2-butyl)benzophenone was synthesized by reaction of o-(2,3-
dimethyl-Z-butyl)phenyl magnesium bromide with benzoyl chloride according to the

route given below:

161

 

 

>_m81 Mg >;—7<H_Cl, C6H6
‘. 2. (CH3)2CO FeCl3 H2804

 

   

 

Brz
11st4
A82504
1. Mg or BuLi Br 1 NaN02
HCl
2. PhCOCl 2. H3P02

 

Scheme 60. Synthesis of 2-(2'-(2',3'-Dimethyl)butyl)benzophenone

2,3-DimethyI-2-butanol

A solution of anhydrous acetone (44.5 g, 0.77 moles) in dry ether was added
dropwise to a stirred mixture of isopropyl magnesium bromide (prepared from 48 g (0.4
moles) of isopropylbromide and 10 g (0.42 moles) magnesium) in ether at -78°C. The
addition took approximately an hour. The mixture was then stirred at room temperature
for an hour and was refluxed overnight. After cooling to room temperature, 50 mL of
10% HCl was added and layers were separated. The aqueous layer was washed four times
with ether and the combined organic layer was washed with water, saturated sodium
bicarbonate and saturated sodium chloride solutions and dried. Solvent removal afforded
a pale yellow oil which was distilled to give 24.8 g (60% yield, 0.24 moles) of product as

g a colorless liquid.

162
'H NMR(CDC13): 5 0.9 (d, 6H), 1.1 (s, 6H), 1.63 (septet, 1H), 2.15 (1H, s, OH)

2-Chloro-2,3-dimethylbutane

To 24.8 g (0.24 moles) of 2,3-dimethyl-2-butanol was added 100 mL of
concentrated hydrochloric acid and the mixture was stirred at room temperature
overnight. The mixture was then poured into a separatory funnel and layers were
separated. The organic layer was washed with water and dried to afford 28.9 g (100%

yield) of the product as a colorless liquid.

'11 NMR(CDC13): 5 0.99 (d, 6H), 1.52 (s, 6H), 1.85 (septet, 1H)

2,3-Dimethyl-2-butyl)benzene

A solution of 2-chloro-2,3-dimethylbutane (11 g, 0.11 moles) in 10 mL of
benzene was added dropwise to a stirred suspension of ferric chloride (27 g, 0.17 moles)
in benzene (30 mL, 0.44 moles) at 0°C. The mixture was allowed to warm to room
temperature and was stirred for 2 hours. The mixture was then allowed to sit and the top
fraction (liquid portion) was removed leaving the solid catalyst behind. Ether was added
and the organic layer was washed with water and dilute alkali and dried. Solvent was

removed to leave 10 g (56%, 0.06 moles) of product as a colorless oil.

.'H NMR(CDC13): 5 0.74 (d, 6H), 1.23 (s, 6H), 1.9 (septet, 1H), 7.1-7.4 (m, 5H)

'-(2,3-Dimethyl-2—bulyl)nitrobenzene
A solution of nitric acid (3.9 mL of 15.5 M solution) in 10 mL of concentrated

sulfuric acid was added dr0pwise to 10 g (0.06 moles) of (2,3-dimethyl-2-butyl)benzene

163

at 0°C. After addition was complete, the mixture was allowed to stir in the ice bath for 0.5
hours before it was poured into a separatory funnel. Layers were separated and the
organic layer was washed with saturated sodium chloride, water, 2N NaOH, and saturated
sodium chloride and dried to leave a yellow oil which was analyzed to contain both ortho
and para isomers. Fractional distillation resulted in recovery of 11.1 g (90% yield) of the

desired product as a pale yellow oil.

lH NMR(CDC13): 5 0.74 (d, 6H), 1.25 (s, 6H), 2.91 (septet, 1H), 7.45 (d, 2H), 8.13 (d,

2H)

'-Bromo-4 '-(2,3-dimethyl-2-butyl)nitrobenzene

In a 500 mL three necked round bottom flask was placed 11.1 g (0.054 moles) of
4'(2,3-dimethyl-2-butyl)nitrobenzene, silver sulfate (17 g, 0.055 moles), and 300 mL of
concentrated hydrochloric acid. The mixture was stirred for 0.5 hours before 2.9 mL
(0.054 moles) of bromine was added dropwise over a period of an hour. The mixture was
allowed to stir at room temperature for an additional five hours and then poured into 1
liter of dilute sodium sulfite solution. The silver bromide was collected by suction
filtration. The filtrate was extracted three times with ether and the combined ether layer
was washed with water, 10% NaOH, water and dried. Solvent removal afforded 9.6 g
(62%, 0.034 moles) of product as a yellow oil. This was used in the next step without

further purification.

lH NMR(CDC13): 5 0.75 (d, 6H), 1.4 (s, 6H), 3.0 (septet, 1H), 7.5 (d, 1H), 8.05 (dd, 1H),

8.4 (d, 1H)

164

'-Bromo-4 '-(2,3-dimethyI-2-buo’l)anilinium chloride
3'-Bromo-4'-(2,3-dimethyl-2-butyl)nitrobenzene (9.6 g, 0.034 moles) was reduced
in a Parr hydrogenator in the presence of 0.15 g platinum(IV) oxide (Aldrich, Adam's
catalyst) in a mixture containing 150 mL of 95% ethanol and 15 mL of concentrated
hydrochloric acid at a pressure of 4750 psi of hydrogen at room temperature. The
hydrogenation took approximately 24 hours. The reaction mixture was filtered through a
celite pad to remove the catalyst. Solvent removal afforded 9.93 g (100% yield, 0.034

moles) of amine hydrochloride as an off-white solid.
lH NMR(acetqne-d6): 6 0.75 (d, 6H), 1.42 (s, 6H), 3.0 (septet, 1H), 7.46 (dd, 1H), 7.65

(d, 1H), 7.80 (d, 1H)

'-(2,3-DimethyI-2-butyl)bromobenzene

To 9.93 g (0.034 moles) of 3'—bromo-4'-(2,3-dimethyl-2-butyl)anilinium chloride
was added 30 mL of concentrated hydrochloric acid. The mixture was diluted with water
to 100 mL and ice chips were added to cool the mixture to 0°C. A solution of sodium
nitrite (2.5 g, 0.036 moles) in 10 mL of water was added to the mixture over a period of
two minutes. The mixture was stirred at 0°C for an additional 15 minutes before it was
vacuum filtered to give a clear yellow solution which was kept at 0°C. A 50% solution of
hypophosphorous acid (70 mL) was added to the filtrate and the mixture was kept in the
freezer for 48 hours. The mixture was then allowed to warm to room temperature and was
extracted with ether three times. The combined ether layer was washed with water and

dried over anhydrous magnesium sulfate. Solvent was evaporated to give a yellow oil

165

which upon Kugelrohr distillation yielded 4.8 g (58% yield, 0.020 moles) of product as a

colorless liquid.

lH NMR(CDC13): 6 0.75 (d, 6H), 1.40 (s, 6H), 3.0 (septet, 1H), 7.0 (dd, 1H), 7.20 (dd,

1H), 7.35 (d, 1H), 7.56 (d, 1H)

2 '-(2,3-Dimethyl-2-butyl) benzoph enone

A solution of benzoyl chloride (3.5 mL, 4.2 g, 0.03 moles) in 20 mL of anhydrous
ether was added dropwise to a stirred solution of 2'-(2,3-dimethyl—2-butyl)phenyl
magnesium bromide (prepared from 4.8 g (0.020 moles) 2'-(2,3-dimethyl-2-
butyl)bromobenzene and 0.6 g magnesium) in anhydrous ether at 0°C. The mixture was
stirred at room temperature for an hour and refluxed overnight. After cooling to room
temperature, water was added and layers were separated. The organic layer was washed
with water, sodium hydroxide, and water and dried. Solvent was evaporated to leave a
yellow oil which was chromatographed (using hexane as eluent) to leave 2.0 g (38%

yield) of product as an off-white solid which was recrystallized from hexane.

lH NMR(CDC13): 5 0.72 (d, J=6.8 Hz, 6H, (CH3)2CH), 1.17 (s, 6H, (CH3)2C ), 2.20
(septet, J=6.8 Hz, 1H, CH(CH3)2), 7.01 (dd, J=7.62, 1.56 Hz, 1H, Ar), 7.18 (ddd, 1:753,
7.35,1.23 Hz, 1H, Ar), 7.36 (ddd, J= 8.22, 7.35, 1.59 Hz, 1H, Ar), 7.41 (dd, J=7.35, 7.0
Hz, 2H, Ar), 7.48 (dd, J=8.22, 1.12 Hz, 1H, Ar), 7.54 (n, 1:735, 1.44 Hz, 1H, Ar), 7.80

(dd, J=7.0, 1.44 Hz, 2H, Ar)

l3C NMR(CDC13): 5 18.0, 25.7, 37.0, 42.4, 124.5, 127.9, 128.3, 128.5, 128.6, 130.4,

133.1, 137.9, 138.9, 148.3, 200.1

166

IR(neat): 3063.4, 2961.1, 2932.1, 1670.5,'1450.6, 1269.3, 1176.7, 1109.2
HRMS: 266.16707 calculated for Cquzzo; found: 266.1665

m.p.: 63-64°C

III. Photochemical Experiments and Procedures

A. Purification of Chemicals

1. Solvents

Benzene- 3.5 liter of reagent grade benzene was mixed with 0.5 liter cone. sulfuric
acid and the mixture was stirred for 2-3 days. The benzene layer was separated and was
washed with 100 mL portions of conc. sulfuric acid several times until the sulfuric acid
layer did not turn yellow. The benzene was then washed with distilled water and saturated
sodium bicarbonate solution. The benzene was separated, dried over magnesium sulfate
and filtered into a 5 L round bottom flask. Phosphorus pentoxide (100 g) was added and
the solution was refluxed for 48 hours. After refluxing, the benzene was distilled through
a one meter column packed with stainless steel helices. The first and the last 10% were
discarded. (b.p.: 78°C)

Methanol- Reagent grade absolute methanol was refluxed over magnesium tumings for 2
hrs. and distilled through a half meter column packed with glass helices. The first and last

10% were discarded.

167

2. Internal Standards

Pentadecane (C15)- Pentadecane (Columbia Organics) was washed with sulfuric acid and
distilled by Dr. Peter J . Wagner.

Hexadecane (C16)- Hexadecane (Aldrich) was washed with sulfuric acid and distilled by
Dr. Peter J. Wagner.

Heptadecane (C17)- Heptadecane (Aldrich) was washed with sulfuric acid and distilled by
Dr. Peter J. Wagner.

Nonadecane (C19)- Nonadecane (Chemical Samples Company) was recrystallized from
ethanol by Dr. Bong-Ser Park

Eicosane (C20)- Eicosane (Aldrich) was purified by recrystallization from ethanol.

Methyl benzoate (MB)- Methyl benzoate was purified by fractional distillation by Dr.

Kung-Lung Cheng.

B. Equipment and Procedures

1. Glassware

All photolysis glassware (pipettes, syringes, volumetric flasks, etc.) were rinsed with
acetone and distilled water and boiled in a solution of Alconox laboratory detergent in
distilled water for 24 hrs. They were rinsed with water and boiled in distilled water for 3-

4 days with the water changed every 24 hrs. After a final rinse with distilled water, the

o o l
glassware was oven dned at 140 C overnight and cooled to room temperature before use.

168

Ampoules used for irradiation were made from 13 x 100 mm Pyrex culture tubes
by flame heating them approximately 2 cm from the top with an oxygen-natural gas torch

and drawing them to a uniform 15 cm length.

2. Sample Preparations

All solutions were prepared by directly weighing the desired material into volumetric
flasks or by dilution of stock solutions. Equal volumes (3.0 mL) of sample were placed

via syringes into each ampoule.

3. Degassing Procedure

Irradiation ampoules were attached to a vacuum line. The ampoules were degassed by
three consecutive freeze-pump-thaw cycles. The ampoules were then sealed with an

oxygen-natural gas torch while still under vacuum.

4. Irradiation Procedures

Small scale irradiations were made by irradiating 0.01 M degassed solutions of the
sample in NMR tubes. The irradiation sources included a medium pressure mercury arc
lamp and a Rayonet reactor. The light from the source was filtered through a Pyrex or

Uranium glass or 313 and 366 nm filter solutions.

169

C. Identification of Photoproducts

Products From a—(2-Ethylphenyl)acetophenone (I)
a—(2—Ethylphenyl)acetophenone (0.0031 g) in 0.75 mL benzene-d6 was irradiated

through Pyrex filter for 15 minutes at room temperature. The signals of two
photoproducts were detectable by NMR. The effect of temperature on product ratios was
investigated by conducting the photochemistry in dry ice-acetone/ethanol, ice-water and
silicon oil (110°C) baths. The diastereomeric ratio of the products were determined by
NMR integration of the methyl doublet signals corresponding to each isomer. Large scale
irradiation using 0.4 g of a-(2-ethy1phenyl)acetophenone in 150 mL of toluene was
performed until no trace of starting material could be observed by NMR. The product
mixture was then separated by PTLC, using 3% ethyl acetate in hexane solution, to
separate the two indanols. The Z-indanol was eluted before the E-indanol. The products

were recovered as oils.

 

lindE lindZ

Scheme 61. Photoproducts of a-(Z-Ethylphenyl)acetophenone

170

Z-l-methyl-2-phenyl-2-indanol

'H NMR(CDC13): 5 1.16 (d, J=7.0 Hz, 3H, CH3), 3.05, 3.40 (AB quartet, J=16.3 Hz, 2H,
CH2), 3.48 (q, J=7.0 Hz, 1H, CH), 7.15—7.3 (m, 5H, Ar), 7.36 (t, J=7.0 Hz, 2H, Ar), 7.60
(d, J=7.0 Hz. 2H, Ar)

lH NMR(Toluene-d8): 5 1.02 (d, J=7.2 Hz, 3H, CH3), 2.8, 3.20 (AB quartet, J=16.3 Hz,
2H, CH2), 3.22 (q, J=7.2 Hz, 1H, CH), 6.9-7.2 (m, 7H, Ar), 7.40 (d, J=7.0 Hz, 2H, Ar)

l3C NMR(CDC13): 5 10.3, 49.3, 50.4, 85.4, 121.7, 124.8, 125.4, 126.9, 127.0, 127.1,
128.2, 140.0, 144.1, 145.0

IR(CC14): 3600, 1175, 1043

E-l~methyl-2-phenyl-Z-indanol

lH NMR(CDC13): 5 0.73 (d, J=7.0 Hz, 3H, CH3), 3.1,3.70 (2H, AB quartet, J=l6.0 Hz,
2H, CH2), 3.23 (q, J=7.0 Hz, 1H, CH), 7.21 (m, 4H, Ar), 7.29 (m, 1H, Ar), 7.34 (t, J=6.6
Hz, 2H, Ar), 7.45 (d, J=6.56 Hz, 2H, Ar)

lH NMR(Toluene-d3): 5 0.69 (d, J=7.5 Hz, 3H, CH3), 2.65, 3.40 (AB quartet, J=15.9 Hz,
2H, CH2), 3.0 (q, J=7.5 Hz, 1H, CH), 6.9-7.2 (m, 9H, Ar)

13
C NMR(CDC13): 5 17.6, 44.6, 52.4, 86.1, 124.3, 124.9, 126.2, 126.9, 127.0, 127.3,
128.1,140.1, 140.2, 146.7

IR(CC14): 3605, 1165, 1050

171

 

fir

 

 

 

 

add I
a. m_l 1
(“—‘I'W f——"'————‘-——’
u o
z
A A

 

 

 

rug—'5"
1
O
11
3
3'
<
I»
l e:
l: >

 

 

Figure 34. 1H NMR of a-(Z-Ethylphenyl)acetophenone Before and After Irradiation

in Toluene (A > 290 nm)

172

Products from a—(2,4,6-Triethylphenyl)acetophenone

a-(2,4,6-Triethylphenyl)acetophenone (0.002 g) in 0.8 mL of deuterated benzene
was irradiated until starting material could not be observed by NMR. The signals
corresponding to two isomeric indanols were detected in the NMR spectrum of the
mixture. The effect of temperature on product ratios was investigated by conducting the
photochemiStry in acetone/ethanol, ice-water and silicon oil (110°C) baths. Solid state
irradiation was performed by packing a melting point capillary with the compound and
irradiating it through Pyrex-filtered uv light for three hours. The diasteriomeric ratio of
the products was determined by NMR integration of the methyl doublet peaks
corresponding to each isomer. Large scale irradiation using 0.35 g of a—(2,4,6-
triethylphenyl)acet0phenone in 150 mL of toluene was performed until 100% conversion
(GC). Solvent was removed to leave a yellow oil which was separated by PTLC using 5%
ethyl acetate in hexane to separate the two isomers. The Z-isomer was eluted before the

E-isomer. The proucts were recovered as oils.

 

 

\\..
Ph
\ hv
/ O Toluene
2 ZindE 2indZ

Scheme 62. Photoproducts of a-(2,4,6-TriethylphenyI)acetophenone

173

Z-l-methyl-4,6-diethyl-Z-Qhenyl-Z-indanol

IH NMR(CDC13): 5 1.25 (t, J=7.5 Hz, 3H, CH3CH2), 1.25 (d, J=7.5 Hz, 3H, CH3CH),
1.32 (3H, t, J: 7.5 Hz, 3H, CH3CH2), 2.1 (s, 1H, 0H), 2.6 (q, J=7.5 Hz, 2H. CHZCH3).
2.7 (q, J=7.5 Hz, 2H, CHzCH3), 3.2, 3.43 (AB quartet, J= 18 Hz, 2H, CH2), 3.6 (q, J=7.5
Hz, 1H, CHCH3), 6.95 (s, 1H, Ar), 6.98 (s, 1H, Ar), 7.3 (1H, t, J=6.7 Hz, 1H, Ar), 7.45
(2H, dd, J= 6.7, 7.0 Hz, 2H, Ar), 7.68 (d, J= 7.0 Hz, 2H, Ar)

lH NMR(Toluene-d8): 5 1.12 (d, J=6.9 Hz, 3H, CH3), 1.15 (t, J=7.8 Hz, 3H, CH3), 1.23
(t, J=7.8 Hz, 3H, CH3), 1.4 (s, 1H, 0H), 2.45 (q, J=7.8 Hz, 2H, CH2), 2.59 (q, J=7.8 Hz,
2H, CH2), 2.88, 3.13 (AB quartet, J=16.2 Hz, 2H, CHZCOH), 3.30 (q, J=7.8 Hz, 1H,
CHCH3), 6.84 (s, 1H, Ar), 6.87 (s, 1H, Ar), 7.11 (t, J= 6.6 Hz, 1H, Ar), 7.21 (dd, J=6.6,
7.2 Hz, 2H, Ar), 7.5 (d, J=7.2 Hz, 2H, Ar)

l3C NMR(CDC13): 5 10.08, 14.21, 15.64, 26.01, 28.62, 47.16, 50.08, 84.88, 120.34,
125.01, 125.70,126.48, 127.76, 135.05,139.81, 143.36,144.04,144.79

IR(CC14): 3592, 2966.9, 2934.1, 2874.2, 1240.4, 1174.8, 991.54, 935.59, 871.94, 700.25

E-l-methyl-4,6—diethyl-2-phenyl-Z-indanol

‘H NMR(CDC13): 5 0.79 (d, J=7.2 Hz, 3H, CH3CH), 1.20 (t, J=7.5 Hz, 3H, CH3CH2),
1.25 (t, J=7.5 Hz, 3H, CH3CH2), 2.0 (broad s, 1H, CH), 2.62 (q, J=7.5 Hz, 2H, CHZCH3),
2.63 (q, J=7.5 Hz, 2H, CHZCH3), 3.12, 3.65 (AB quartet, J=18 Hz, 2H, CH2), 3.39 (q, J=
7.2 Hz, 1H, CHCH3), 6.90 (s, 1H, Ar), 6.92 (s, 1H, Ar), 7.25-7.5 (m, 5H, Ar)

lH NMR(Toluene-d3): 5 0.78 (d, J=6.9 Hz, 3H, CH3CH), 1.15 (t, J=7.5 Hz, 3H,

CH3CH2), 1.23 (t, J=7.5 Hz, 3H, CH3CH2)s 1.4 (broad s, 1H, OH), 2.44 (q, J=7.5 Hz, 2H,

174

CHZCH3), 2.59 (q, J=7.5 Hz, 2H, CHZCH3), peaks between 3.0-7.5 overlapped with those

from the major isomer.

l3C NMR(CDC1,): 5 14.52, 15.82, 17.84, 26.48, 28.87, 42.53, 52.55, 85.98, 121.30,
125.35, 125.89, 126.17, 127.26, 128.09,135.18, 140.02, 143.30, 146.80

IR(CCI4): 3472, 2968.8, 2930.24, 2872.37, 1277, 1211.4, 1066.8, 881.58, 746.55, 700.25

Products from a-(o- Tolprropiophenone (3)

a—(o-Tolyl)propiophenone (0.002 g) in 0.8 mL of deuterated benzene was
irradiated until starting material could not be observed by NMR. The signals
corresponding to several products were detected in the NMR spectrum of the mixture.
These products were identified as two isomeric 2-phenyl-2-indanols, two isomeric
diarylethanes, B-tolylpropiophenone and benzaldehyde. The effect of temperature on
product ratios was investigated by conducting photochemistry in dry ice-ethanol, ice-
water and silicon oil (110°C) baths. The diasteriomeric ratio of indanols was determined
by NMR integration of the methyl doublet signals corresponding to each isomer. Large
scale irradiation using 0.3 g of a-(o-tolyl)propiophenone in 150 mL of methanol was
performed until 100% conversion by NMR. The products were separated by PTLC using
5% ethyl acetate in hexane as eluent and characterized. Two additional products which
were identified as two isomeric 1-phenyl-2-tolyl-1-propanols were also recovered. The

order of elution was as follows: diarylethenes followed by B-tolylpropiophenone, the Z-

indanol, the E-indanol and photoreduction products. The products were recovered as oils.

 

175

 

 

 

 

 

W

Haw-r w—a
1.8. I.“
1.48

7.16
4.1. 0 31

 

 

Figure 35. 1H NMR Spectra of a-(2,4,6-Triethylphenyl)acetophenone Before and
After Irradiation in Toluene (D290 nm)

 

3cleav-Two isomers 3red-Two isomers

Scheme 63. Photoproducts of a-Tolylpropiophenone

Z-l-meth 1-2- hen l-2-indanol

 

lH NMR(CDC13): 5 1.16 (d, J=7.0 Hz, 3H, CH3), 3.05, 3.40 (AB quartet, J=16.3 Hz, 2H,
CH2), 3.48 (q, J=7.0 Hz, 1H, CH), 7.15-7.3 (m, 5H, Ar), 7.36 (t, J=7.0 Hz, 2H, Ar), 7.60
(d, J=7.0 Hz, 2H, Ar)

l3C NMR(CDCl3): 5 10.3, 49.3, 50.4, 85.4, 121.7, 124.8, 125.4, 126.9, 127.0, 127.1,
128.2, 140.0, 144.1, 145.0

IR(CC14): 3600, 1175, 1043

E-l-methyl-2-phenyl-2-indanol

IH NMR(CDCl3): 5 0.73 (d, J=7.0 Hz, 3H, CH3), 3.10,3.70 (2H, AB quartet, J=16.0 Hz,
2H, CH2), 3.23 (q, J=7.0 Hz, 1H, CH), 7.21 (m, 4H, Ar), 7.29 (m, 1H, Ar), 7.34 (t, J=6.6
Hz, 2H, Ar), 7.45 (d, J=6.56 Hz, 2H, Ar)

l3C NMR(CDC13): 5 17.6, 44.6, 52.4, 86.1, 124.3, 124.9, 126.2, 126.9, 127.0, 127.3,

128.1,140.1,140.2,146.7

177

IR(CC14): 3605, 1165, 1050

(33) and (S,S)-1-Phenyl-2-tolyl-l-propanol

lH NMR(CDC13): 5 0.95 (d, J=7.0 Hz, 3H, CH3CH), 2.15 (s, 3H, CH3Ar), 3.25 (dq,

J=7.0, 6.7 HZ, 1H, CHCH3 ), 4.47 (d, J=6.7 Hz, 1H, CHOH), 7.0-7.3 (m, 9H, Ar)

(3,8) and 1S,R)-l-Phenyl-2-tolyl-l-propanol

IH NMR(CDC13): 5 1.30 (d, J=7.0 Hz, 3H, CH3C1-1), 1.92 (s, 3H, CH3Ar), 3.25 (dq,

J=7.0, 6.7 Hz, 1H, CHCH3), 4.47 (d, J: 6.7 Hz, 1H, CHOH), 7.0-7.3 (m, 9H, Ar)

1,2-Ditolylbutanes

lH NMR(CDC13): 5 1.0 (d, J=7.0 Hz, 6H,2CH3C1~I), 1.20 (d, J: 7.0 Hz, 6H, 2CH3CH),

2.0 (s, 6H, 2CH3Ar), 2.2 (s, 6H, 2CH3Ar), 3.15 (m, 4H, CHCH3), 6.8-7.3 (m, 16H, Ar)

Products from a—(2-Ethylphenyl)-,6,,6,,6—trideuteropropiophenone and/or a-(2-
Ethylphenybpropiophenone (4, 4d 3)

a—(2—Ethylphenyl)-B,[3,B-tfideuteropropiophenone (0.003 g) in 0.8 mL of
deuterated benzene was irradiated until no trace of starting material could be observed by
NMR. A mixture of several products including two isomeric indanols, two isomeric
diphenylethanes, and benzaldehyde were detected, by their signals, upon analysis of the
NMR spectrum of the photolysis mixture. The effect of temperature and phase on product
ratios was also investigated by conducting the photochemistry in acetone/ethanol, ice-

water and silicon oil (110°C) baths and in solid. The diasteriomeric ratio of indanols was

178

determined by NMR integration of the methyl doublet signals corresponding to each
isomer. Large scale irradiation using 0.25 g of a—(2-ethylphenyl)-B,B,B—trideutero
propiophenone in 100 mL of benzene was performed. Solvent was evaporated to leave a
colorless oil which was chromatographed by preparative scale tlc using 3% ethyl acetate
in hexane solution. The order of elution was as follows: diarylethenes, the Z-indanol, the
E-indanol and photoreduction products. The indanols and photoreduction products were

recovered as oils.

 

4cleav-Two isomers 4red-Two isomers

Scheme 64. Photoproducts of a-(Z-Ethylphenyl)—B,B,B-trideuteropropiophenone

Z-l-Meth l-Z-3-trideuterometh 1-2- hen l-2-indanol

 

lH NMR(CDC13): 5 1.19 (d, J=7.0 Hz, 3H, CH3CH), 1.52 (broad s, 1H, 0H), 3.50 (s, 1H,
CHCD3), 3.50 (q, J=7.0 Hz, 1H, CHCH3), 7.18 (dd, 1:0.7, 4.5 Hz, 1H, Ar), 7.20 (broad,
1H, Ar), 7.25-7.27 (m, 2H, Ar), 7.29 (t, J=7.7 Hz, 1H, Ar), 7.38 (dd, J=7.7, 7.1 Hz, 2H,

Ar), 7.60 (d, J=7.1 Hz, 2H, Ar)

179

'H NMR(Toluene-d8): 5 0.92 (d, J=7.2Hz, 3H, CH3CH), 3.12 (s, 1H, CHCD3), 3.12 (q,
J=7.2 Hz, 1H, CHCH3), 7.0-7.6 (m, 9H, Ar)

2H NMR(CC14): 5 1.29 (s, 3D)

l3C NMR(CDC13): 5 9.90, 9.91 (septet), 50.05, 88.23, 123.35, 125.7, 126.9, 127.16.

128.1, 144.3

IR(CC14): 3588, 2966, 2932, 2224, 1489, 1176.7, 1055, 985.8, 951, 912.4, 871.9, 746.5

(Z,Z)-lé-Dimethyl-2-phenyl-2-indanol

lH NMR(CDC13): 5 1.19 (d, J=7.0 Hz, 6H, 2CH3CH), 1.52 (broad s, 1H, OH), 3.50 (q,
J=7.0 Hz, 2H, 2CHCH3), 7.18 (dd, J=0.7, 4.5 Hz, 1H, Ar), 7.20 (broad, 1H, Ar), 7.25-
7.27 (m, 2H, Ar), 7.29 (t, J=7.7 Hz, 1H, Ar), 7.38 (dd, J=7.7, 7.1 Hz, 2H, Ar), 7.60 (d,
J=7.1 Hz, 2H, Ar)

111 NMR(Toluene-d8): 5 0.92 (d, J=7.2Hz, 6H, 2CH3CH), 3.12 (q, J=7.2 Hz, 2H,

2CHCH3), 7.0-7.6 (m, 9H, Ar)

l3C NMR(CDC13): 5 9.90, 9.91, 50.05, 88.23, 123.35, 125.7, 126.9, 127.16, 128.1, 144.3

IR(CC14): 3588, 2966, 2932, 1489, 1176.7, 1055, 985.8, 951, 912.4, 871.9, 746.5, 700.25

E-l-methyl-Z-3-trideuteromethyl-Z-phenyl-Z-indanol

lH NMR(CDC13): 5 0.74 (d, J=7.35 Hz, 3H, CH3CH), 1.65 (broad s, 1H, OH), 3.28 (q,
1:740 Hz, 1H, CHCH3), 3.90 (s, 1H, CHCD3), 7.20-7.28 (m, 4H, Ar), 7.32 (t, J=7.2 Hz,

1H, Ar), 7.37 (dd, J=7.35, 7.2 Hz, 2H, Ar), 7.52 (d, J=7.35 Hz, 2H, Ar)

180

1H NMR(Toluene-d8): 5 0.55 (d, J=7.5Hz, 3H, CH3CH), 2.95 (q, J=7.5 Hz, 1H, CHCH3),
3.43 (s, 1H, CHCD3), 7.0-7.6 (m, 9H, Ar)
2H NMR(CC1,): 5 1.4 (s, 3D)

”C NMR(CDC13): 5 11.1 (septet), 18.3, 43.3, 52.5, 79.9, 123.9, 124.4, 126.0, 126.58,
127.1, 127.3, 127.9, 1282,1283, 128.7

IR(CC14): 3470, 2966.9, 2932.2, 2874, 2229.9, 1223, 1062, 970, 870, 740.7

1LLZHé-Dimethyl-Z-phenyI-2-indanol

 

lH NMR(CDC13): 5 0.74 (d, J=7.4 Hz, 3H, CH3CH), 1.34 (d, J=7.3 Hz, 3H, CH3CH),
1.65 (broad s, 1H, OH), 3.28 (q, J=7.40 Hz, 1H, CHCH3), 3.90 (q, J=7.3 Hz, 1H,
CHCH3), 7.20-7.28 (m, 4H, Ar), 7.32 (t, J=7.2 Hz, 1H, Ar), 7.37 (dd, J=7.35, 7.2 Hz, 2H,
Ar), 7.52 (d, J=7.35 Hz, 2H, Ar)

lH NMR(Toluene-d8): 5 0.55 (d, J=7.5Hz, 3H, CH3CH), 1.1 (d, J=7.4 Hz, 3H, CH3CH),
2.95 (q, J=7.5 Hz, 1H, CHCH3), 3.43 (q, .1: 7.4 Hz, 1H, CHCH3), 7.0-7.6 (m, 9H, Ar)

l3C NMR(CDC13): 5 11.1, 18.3, 43.3, 52.5, 79.9, 123.9, 124.4, 126.0, 126.58, 127.1,
127.3, 127.9, 128.2, 128.3, 128.7

IR(CC14): 3470, 2966.9, 2932.2, 2874, 1223, 1062, 970, 870, 740.7

(M) and (S,S)—2,§-di(ethylphenyl)butane
lH NMR(CDC13): 5 1.09 (t, J=7.48 Hz, 3H, CH3CH2), 1.27 (3H, t, 1:754 Hz, 3H,
CH3CH2), 2.36 (dq, J=7.42, 14.56 Hz, 1H, CHZCH3), 2.60 (dq, J=7.47, 14.56 Hz, 1H,

CHZCH3), 2.72 (1H, dq, J=7.49, 14.49 Hz, 1H, CHZCH3), 2.84 (dq, J=7.41, 14.56 Hz, 1H,

181

CHZCH3), 3.20 (s, 1H, CHCD3), 3.26 (s, 1H, CHCD3), 6.96 (1H, dt, J=2.l9, 7.7 Hz, 1H,
Ar), 6.98 (dt, J=1.38, 7.5 Hz, 1H, Ar), 7.05 (dt, J=2.19, 7.7 Hz, 1H, Ar), 7.15 (dt, J=l.37,
7.7 Hz, 1H, Ar), 7.19 (dt, J=2.14, 7.7 Hz, 1H, Ar), 7.23 (broad d, J=7.7 Hz, 1H, Ar), 7.25

(dt, J=1.98, 7.5 Hz, 1H, Ar), 7.34 (broad d, J=7.41 Hz, 1H, Ar)

l3C NMR(CDCl3): 5 15.5, 15.89, 20.84, 21.33, 25.54, 26.33, 39.84, 40.34, 125.45, 125.7,

125.8, 126.27, 126.51, 128.15, 128.68, 140.5, 141.99, 144.46, 144.51

(LLS) and (S,R EZQ-dilethylphenylwutane

lH NMR(CDC13): 5 1.05 (t, J=7.60 Hz, 6H, 2 CH3CH2), 2.34 (dq, J=7.63, 14.35 Hz, 2H,
CHZCH3), 2.58 (dq, J=7.69, 14.56 Hz, 2H, CHZCH3), 3.25 (broad s, 2H, 2CHCD3). 6.94
(dt, 1:2.19, 7.5 Hz, 2H, Ar), 6.96 (dt, 1:1.35, 7.5 Hz, 2H, Ar), 7.03 (dt, J=2.19, 7.5 Hz,

2H, Ar), 7.21 (broad d, J=7.42 Hz, 2H, Ar)

l3C NMR(CDC13): 5 15.5, 20.84, 25.54, 39.83, 125.43, 126.50, 128.15

l-Phen 1-2- 2’-eth l hen 1 3 -trideutero-1- ro anol one isomer

lH NMR(CDC13): 5 1.10 (t, J= 7.6 Hz, 3H, CH3CH2), 2.5 (AB quartet of q, J=7.6 Hz,

1:15 Hz, 2H, CH2CH3), 3.35 (d, 1H, CHCD3), 4.8 (d, 2H, CHOH), 7.1—7.5 (m, 9H, Ar)

l-Phen 1-2- 2’-eth l hen l -trideutero-1- ro anol second isomer

lH NMR(CDC13): 5 1.25 (t, J: 7.6 Hz, 3H, CH3CH2), 2.7 (AB quartet of q, J=7.6, 15 Hz,

2H, CHZCH3), 3.35 (d, 1H, CHCD3), 4.7 (d, 2H, CHOH), 7.1-7.5 (m, 9H, Ar)

182

CH3 CH3
P“ hv OH " OH
O ' 4., + ’a. +Typel
P" A
CH3 01-13
A B 1

 

 

 

 

 

 

Figure 36. 1H NMR Spectra of ar(2-Ethylphenyl)propiophenone Before and After
Irradiation in Toluene (D290 nm)

183

Products from a—(2,4,6-Triethylphenyl)-fl,,6,,6—trideuteropropiophenone and/or a-
(2,4,6-Triethylphenybpropiophenone (5, 5d3)
01—(2,4,6-Triethylphenyl)-[3,0,B-trideuteropropiophenone (0.005 g) in 0.8 mL of
deuterated benzene was irradiated until no trace of starting material could be observed by
NMR. The signals for two isomeric indanols were detected upon analysis of the NMR
spectrum of the photolysis mixture. In our investigation we separated the products from
both the deuterated and fully protanated species. The effect of temperature and phase on
product ratios was also investigated by conducting the photochemistry in acetone/ethanol,
ice-water and silicon oil (110°C) baths and in solid. The diasteriomeric ratio of indanols
was determined by NMR integration of methyl doublet signals corresponding to each
isomer. In order to separate the two indanols, large scale irradiation using 0.30 g of or-
(2,4,6-'triethylphenyl)-B,[3,B—trideuteropropiophenone in 100 mL of benzene was
performed. Solvent was evaporated to leave a yellow oil which was chromatographed by
PTLC 7% ethyl acetate in hexane solution. The plate had to be diluted several times to

separate the two isomers (oils). The ZE-isomer was the top fraction eluted.

Ph
hv

fl

0 Toluene

 

5 SindZE 5indEZ

Scheme 65. Photoproducts of a-(2,4,6-Triethylphenyl)B,B,[3-trideutero

propiophenone

184

4 6-Dieth l-Z-l-trideuterometh I-E-3-meth l-2- hen l-2-indanol

'H NMR(CDCl3): 5 0.86 (d, J=7.14 Hz, 3H, CH3CH), 1.24 (t, J=7.8 Hz, 3H, CH3CH2),
1.29 (t, J=7.8 Hz, 3H, CH3CH2), 2.0 (broad s, 1H, OH), 2.6 (q, J=7.8 Hz, 2H, CHZCH3),
2.7 (dq, J=7.8, 14.5 Hz, 2H, CHZCH3), 3.45 (q, J=7.1 Hz, 1H, CHCH3), 3.6 (broad s, 1H.
CHCD3), 6.74 (s, 1H, Ar), 6.90 (s, 1H, Ar), 7.15-7.3 (m, 5H, Ar)

lH NMR(Toluene-d8): 5 0.92 (d, J=7.2 Hz, 3H, CH3CH), 1.16-1.3 (m, 6H), 2.0 (broad s,
1H, OH), 2.5 (dq, J=7.2, 14.4 Hz, 2H, CHZCH3), 2.6 (q, J=7.5Hz, 2H, CH2CH3), 3.20 (q,
J=7.1 Hz, 1H, CHCH3), 3.34 (broad s, 1H, CHCD3), 6.8-7.3 (m, 7H, Ar)

2H NMR(CC14): 5 1.48 (s, 3D)

l3C NMR(CDC13): 5 13.62, 14.4 (septet), 14.77, 15.22, 24.84, 28.42, 46.29, 48.80, 86.20,

120.22, 125.42, 126.05, 126.42, 127.38, 138.45, 140.95, 142.90, 144.10, 144.44

IR(CC14): 3470.2, 3061.4, 2966.9, 2932.2, 2874.3, 2230, 1280.9, 1062.9, 970.3, 870,

806.4, 740.7

4.6-Dietl_1yl-Z.Eiidimethvl—Z-phenyl-Z-indanol

lH NMR(CDC13): 5 0.86 (d, J=7.14 Hz, 3H, CH3CH), 1.24 (t, J=7.8 Hz, 3H, CH3CH2),
1.29 (t, J=7.8 Hz, 3H, CH3CH2), 1.47 (d, J=7.2 Hz, 3H, CH3CH), 2.0 (broad s, 1H, OH),
2.6 (q, J=7.8 Hz, 2H. CH,CH,), 2.7 (dq, J=7.8, 14.5 Hz, 2H, CHZCH3), 3.45 (q, J=7.1 Hz,
1H, CHCH3), 3.6 (q, J=7.2, 1H, CHCH3), 6.74 (s, 1H, Ar), 6.90 (s, 1H, Ar), 7.15—7.3 (m,

5H, Ar)

185

lH NMR(Toluene-d8): 5 0.92 (d, J=7.2 Hz, 3H, CH3CH), 1.16-1.3 (m, 9H), 2.0 (broad s,
1H, OH), 2.5 (dq, J=7.2, 14.4 Hz, 2H, CHZCH3), 2.6 (q, J=7.5Hz, 2H, CHZCH3), 3.20 (q.
J=7.1 Hz, 1H, CHCH3), 3.34 (q, J=7.2 Hz, 1H, CHCH3), 6.8-7.3 (m, 7H, Ar)

l3C NMR(CDC13): 5 13.62, 14.4, 14.77, 15.22, 24.84, 28.42, 46.29, 48.80, 86.20, 120.22,
125.42, 126.05, 126.42, 127.38, 138.45, 140.95, 142.90, 144.10, 144.44

IR(CC14): 3470.2, 3061.4, 2966.9, 2932.2, 2874.3, 1280.9, 1062.9, 970.3, 870, 806.4,

740.7

4 6-Dieth l-E-l-trideuterometh I-Z-3-meth 1—2- hen l-2-indanol

   

lH NMR(CDC13): 5 1.291 (t, J=7.56 Hz, 3H, CH3CH2), 1.294 (t, J=7.56 Hz, 3H,
CH3CH2), 1.36 (d, J=7.0 Hz, 3H, CH3CH), 2.0 (broad s, 1H, 0H). 2.6 (dq, J=7.56, 14.3
Hz, 2H, CH2CH3), 2.7 (q, J=7.8 Hz, 2H, CHZCH3), 3.30 (broad s, 1H, CHCD3) , 3.95 (q,
J=7.0 Hz, 1H, CHCH3),6.92 (s, 2H, Ar), 7.30 (t, J=7.3 Hz, 1H, Ar), 7.40 (2H, dd, J=7.3,

7.5 Hz, 2H, Ar), 7.6 (d, J=7.5 Hz, 2H, Ar)

lH NMR(Toluene-d8): 5 1.32 (d, J=7.2 Hz, 3H, CH3CH), 1.16-1.3 (m, 6H), 2.0 (broad s,
1H, OH), 2.52 (dq, J=7.2, 14.4 Hz, 2H, CH2CH3), 2.61 (q, J=7.5Hz, 2H, CHZCH3), 3.32
(broad s, 1H, CHCD3), 3.71 (q, J=7.1 Hz, 1H, CHCH3), 6.8-7.3 (m, 7H, Ar)

2H NMR(CC1,): 5 0.816 (s, 3D)

l3C NMR(CDC13): 5 10.58, 15.28, 15.72, 17.20 (septet), 24.95, 28.95, 42.20, 50.65,

87.92, 121.04, 126.08, 126.70, 127.26, 128.24, 139.92, 141.20, 141.73, 143.42, 143.84

IR(CC14): 3572, 3061.4, 3030.6, 2966.9, 2932.2, 2230, 1282.8, 1033.9, 987.6, 951, 871.9,

787

186

 

 

 

 

 

 

 

Figure 37. 'H NMR Spectra of a-(2,4,6-Triethylphenyl)propiophenone Before and
After Irradiation in Toluene (D290 nm)

187

4,6—DiethyI-E,Z-lé-dimethyl-Z-phenyl—Z-indanol

lH NMR(CDC13): 5 0.82 (d, J=7.0 HZ, 3H, CH3CH), 1.291 (t, J=7.56 Hz, 3H, CH3CH2),
1.294 (t, J=7.56 Hz, 3H, CH3CH2), 1.36 (d, J=7.0 Hz, 3H, CH3CH), 2.0 (broad s, 1H,
OH), 2.6 (dq, J=7.56, 14.3 Hz, 2H, CHZCH3). 2.7 (q, J=7.8 Hz, 2H, CHZCH3), 3.30 (q,
J=7.0 Hz, 1H, CHCH3) , 3.95 (q, J=7.0 Hz, 1H, CHCH3),6.92 (s, 2H, Ar), 7.30 (t, J=7.3
Hz, 1H, Ar), 7.40 (2H, dd, J=7.3, 7.5 Hz, 2H, Ar), 7.6 (d, J=7.5 Hz, 2H, Ar)

lH NMR(Toluene-d8): 5 0.8 (d, J=7.1 Hz, 3H, CH3CH), 1.16-1.3 (m, 9H), 2.0 (broad s,
1H, OH), 2.52 (dq, J=7.2, 14.4 Hz, 2H, CHZCH3), 2.61 (q, J=7.5Hz, 2H, CHZCH3), 3.32
(q, J=7.1 Hz, 1H, CHCH3), 3.71 (q, J=7.1 Hz, 1H, CHCH3), 6.8-7.3 (m, 7H, Ar)

l3C NMR(CDCl3): 5 10.58, 15.28, 15.72, 17.20, 24.95, 28.95, 42.20, 50.65, 87.92,
121.04, 126.08, 126.70, 127.26, 128.24, 139.92, 141.20, 141.73, 143.42, 143.84

IR(CC14): 3572, 3061.4, 3030.6, 2966.9, 2932.2, 1033.9, 987.6, 951, 871.9, 787

Products from a—(2-Benzylphenyl)acetophenone (6)

or—(2-Benzylphenyl)acetophenone (0.003 g) in 0.8 mL of deuterated benzene was
irradiated until no trace of starting material could be detected by NMR. The signals for
two isomeric indanols in a 1:1 ratio were detected. NOe experiments were performed on
isolated indanols to correctly assign their stereochemical arrangement. The effect of
temperature and phase on product ratios was also investigated by conducting the
photochemistry in acetone/ethanol, ice-water and silicon oil (110°C) baths and in solid.
The diasteriomeric ratio of indanols was determined by NMR integration of the

methylene (AB quartet) signals corresponding to each isomer. Large scale irradiation (0.4

188

g in 100 mL benzene) was performed and the two indanols were separated by preparative
scale tlc using 5% ethyl acetate in hexane solution. The Z-indanol was the first eluted

isomer.

Ph

0

 

6 6indZ 6indE

Scheme 66. Photoproducts of a-(2-Benzy1phenyl)acetophenone

Z-lg-diphenyl-Z-indanol

1H NMR(CDC13): 5 1.85 (s, 1H, OH), 3.4, 3.65 (AB quartet, J=16.5 Hz, 2H, CH2), 4.95
(s, 1H, CHPh), 7.05 (dd, J= 7.38, 2.97 Hz, 2H, Ar), 7.12 (d, J= 7.41 Hz, 1H, Ar), 7.2-7.45
(m, 9H, Ar), 7.53 (d, J= 7.38 Hz, 2H, Ar)

lH NMR(Toluene-d8): 5 1.85 (s, 1H, OH), 3.22, 3.33 (AB quartet, J=16.2 Hz, 2H, CH2),
4.64 (s, 1H, CHPh), 7.00-7.6 (m, 14H, Ar)
l3C NMR(CDC13): 5 48.93, 63.92, 84.99, 124.85, 125.36, 125.49, 126.84, 127.46, 127.64,

128.04, 128.48, 129.97, 136.15, 141.71, 142.74, 145.18

IR(CC14): 3557, 3030.6, 1495, 1452.6, 1286.7, 1053.3, 702.18
Noe (CDC13): irradiation of the peak at 5 1.85 (OH) enhanced peaks at 3.4 ppm (2%),

and 7.0-7.6 ppm (25%)

189

Irradiation of the peak at 5 4.95 ppm (methine) enhanced peaks at 3.4 ppm (2.5%), 3.65
ppm (2.1%), 7.05,7.12 ppm (27%), 7.2-7.45 ppm (18.6%), and 7.53 ppm (3.0%)
Irradiation of the peak at 5 3.65 ppm enhanced peaks at 3.4 ppm (37%), 4.95 ppm
(1.3%), and 7.0-7.4 ppm (32%)

Irradiation of the peak at 5 3.4 ppm enhanced peaks at 1.85 ppm (3.8%), 3.65 ppm (22%),

and 7.0-7.6 ppm (16%)

E—l -di hen l-2-indanol

lH NMR(CDC13): 5 2.45 (broad s, 1H, OH), 3.30, 3.85 (AB quartet, J=16 Hz, 2H, CH2),
4.61 (s, 1H, CHPh), 6.61 (dd, J=7.86, 1.92 Hz, 2H, Ar), 6.90-7.10 (m, 8H, Ar), 7.13 (1H,
d, J=7.71 Hz), 7.25 (t, J=7.14 Hz, 1H, Ar), 7.34 (t, J=7.14 Hz, 1H, Ar), 7.43 (d, J=7.2 Hz,
1H, Ar)

'H NMR(Toluene-d3): 5 1.85 (s, 1H, 0H), 2.94. 3.53 (AB quartet, J=16.2 Hz, 2H, CH2),
4.45 (s, 11-1,CHPh), 6.8-7.6 (m, 14H, Ar)

”C NMR(CDC13): 5 46.0, 65.18, 87.3, 124.6, 125.96, 126.0, 126.3, 126.87, 127.2, 127.4,
127.6, 128.9, 139.6, 141.5, 142.64, 144.0

IR(CC14): 3560, 3030.5, 1495, 1286, 702.3
Noe (CDC13): irradiation of the peak at 5 2.45 ppm (OH) enhanced peaks at 3.3 ppm

(1%), and 4.61 (2.1%)
Irradiation of the peak at 5 4.61 ppm (methine) enhanced peaks at 2.45 ppm (5.5%), 6.60

ppm (12%), and 6.9-7.1 ppm (14.5%)

190

Irradiation of the peak at 5 6.60 ppm enhanced peaks at 3.3 ppm (3%), 4.61 ppm

(7.75%), and 6.9-7.14 ppm (24%).

Products from a—(Z-Benzylphenyl)propiophenone ( 7)

a-(2-Benzylphenyl)propiophenone (0.005 g) in 0.8 mL of deuterated benzene
was irradiated until no trace of starting material could be observed by NMR. The signals
for two isomeric indanols and two diarylethanes were detected upon analysis of the NMR
spectrum of the photolysis mixture. The diasteriomeric ratio of indanols was determined
by NMR integration of methyl doublet signals corresponding to each isomer. Products
were separated by performing large scale irradiation using 0.30 g of 01—(2-
benzylphenyl)propiophenone in 100 mL of benzene. Solvent was evaporated to leave a
yellow oil which was chromatographed by PTLC using 3% ethyl acetate in hexane
solution. The diarylbutanes moved with the solvent line and had a rf value of nearly 1.0,
the indanols had an rf value of nearly 0.4 with the ZZ-indanol having a slightly higher
value. The indanols were recovered as oils.

Ph

/

\

 

7cleav-Two isomers

Scheme 67. Photoproducts of a—(Z-Benzylphenyl)propiophenone

191

 

 

 

 

 

Figure 38. 1H NMR Spectra of a-(2-BenzylphenyI)acetophenone Before and After

Irradiation in Toluene (2)290 nm)

192

Z-l-meth 1-3 -di hen l-Z-indanol

lH NMR(CDC13): 5 1.30 (d, J= 6.72 Hz, 3H, CH3CH), 2.20 (broad s, 1H, OH), 3.95 (q,
J=6.72 Hz, 1H, CHCH3), 4.50 (s, 1H, CHPh), 6.50 (dd, J=7.7, 1.9 Hz, 2H, Ar), 6.9-7.3
(10H, m, Ar), 7.4 (d, J=7.0 Hz, 2H, Ar)

l3C NMR(CDC13): 5 10.9, 44.8, 64.8, 88.8, 123.9, 126, 126.2, 126.3, 126.9, 127.5, 127.6,
127.7, 128.1, 128.8, 139.9, 141.2, 143.4, 145.8

IR(CC14): 3570, 3065.3, 3028.6, 2963, 2932.2, 1475.9, 1275.1, 1076.4, 1032, 951, 873.8,

785.1, 729.2, 702.18

Z-l-methyl-3 (Z),2-diphenyl-2-indanol

1H NMR(CDC13): 5 1.25 (d, J= 6.72 Hz, 3H, CH3CH), 1.60 (broad s, 1H, OH), 3.66 (q,
J=6.72 Hz, 1H, CHCH3), 4.95 (s, 1H, CHPh),7.0 (dd, J=7.4, 3.0 Hz, 2H, Ar), 7.10 (d, J:
7.4 Hz, 1H, Ar), 7.2-7.4 (m, 9H, Ar), 7.5 (d, J= 6.9 Hz, 2H, Ar)

l3C NMR(CDC13): 5 10.2, 50.6, 62.8, 87.8, 123.3, 125.2, 125.8, 126.8, 126.9, 127.5, 128,
128.4, 130, 136, 141.8, 143.4, 145.9

IR(CC14): 3584, 3065.3, 2966.9, 2928.3, 1495, 1176.7, 1076.4, 972.3, 873.9, 729.2, 698.3

2R1SléRiS)-Di(2’-ben_zylphenyl)butane

lH NMR(CDC13): 5 0.6 (d, J= 6.72 Hz, 6H, 2CH3CH), 3.10 (broad, 2H, 2CHCH3), 4.0

(AB quartet, J= 15.8 Hz, 4H, 2CH2Ph), 6.8-7.3 (m, 18H, Ar)

13C NMR(CDC13): 5 20.7, 38.7, 40.4, 125.6, 125.8, 126.4, 126.9, 128.8, 130.1, 138.3,

141.1,145.4

193

2R(SL381R)-Di(2’-begglphenyl)butane

IH NMR(CDC13): 5 1.10 (d, J: 6.72 Hz, 6H, 2CH,CH), 3.20 (broad, 2H, 20101,), 3.7

(AB quartet, J= 15.8 Hz, 4H, 2CH2Ph), 6.8-7.3 (m, 18H, Ar)

l3C NMR(CDC13): 5 20.5, 38.7, 39.6, 125.4, 125.9, 126.3, 126.8, 128.7, 130.7, 137.5,

141.2, 145.3

Products from a-Mesifllpropiophenone (8)

a—Mesitylpropiophenone (0.002 g) in 0.8 mL of deuterated benzene was
irradiated until no trace of starting material could be observed by NMR. The signals for
two isomeric indanols were detected upon analysis of the NMR spectrum of the
photolysis mixture. In our investigation, photochemistry was conducted at various
temperatures to ascertain the effect of temperature on product ratios. The diasteriomeric
ratio of indanols was determined by NMR integration of the methyl doublet signals
corresponding to each isomer. In order to separate the two indanols, large scale irradiation
using 0.25 g of a—mesitylpropiophenone in 100 mL of benzene was performed. Solvent
was evaporated to leave a colorless oil which was chromatographed by PTLC using 3%

ethyl acetate in hexane solution. The Z-isomer was the first compound eluted.

O Toluene

   

8 8indZ 8indE

Scheme 68. Photoproducts from a-Mesitylpropiophenone

194

Z-l,5,7-Trimethyl-2-phenyl-Z-indanol

lH NMR(CDC13): 5 1.36 (d, J=7.0 Hz, 3H, CH3CH), 2.10 (broad s, 1H, OH), 2.35 (s, 3H,
CH3Ar), 2.37 (s, 3H, CH3Ar), 3.35 (AB quartet, J=15.6 Hz, 2H, CH2), 3.55 (q, J=7.0 Hz,
1H, CHCH3), 6.90 (s, 1H, Ar), 6.95 (s, 1H, Ar), 7.10 (t, J=6.8 Hz, 1H, Ar), 7.25 (2H, dd,
J=6.8, 7.0 Hz, 2H, Ar), 7.53 (d, J= 7.0 Hz, 2H, Ar)

lH NMR(Toluene-d3): 5 1.15 (d, J=7.2 Hz, 3H, CH3CH), 1.7 (broad s, 1H, OH), 2.06 (s,
3H, CH3Ar), 2.15 (s, 3H, CH3Ar), 3.05, 3.12 (AB quartet, J=15.9 Hz, 2H, CH2), 3.23 (q,

J= 7.2 Hz, 1H, CHCH3), 6.90-7.5 (m, 7H, Ar)

l3C NMR(CDC13): 5 13.18, 18.77, 20.80, 47.42, 49.48, 83.55, 122.47, 124.76, 126.46,
127.74, 129.37, 133.5, 136.26, 139.72, 140.65, 146.52

IR(CC14): 3602, 2976, 2939, 1455, 1374, 1248.9, 1036, 845.5, 700.25

E-l,5,7-Trimethyl-2-phenyI-Z-indanol

lH NMR(CDC13): 5 0.70 (d, J=7.0 Hz, 3H, CH3CH), 2.0 (1H, broad s, 1H, 0H), 2.99 (s,
3H, CH3Ar), 2.31 (s, 3H, CH3Ar), 3.0,3.85 (AB quartet, 1=15.4 Hz, 2H, CH2), 3.35 (q,
J=7.0 Hz, 1H, CHCH3), 6.85 (s, 1H, Ar), 7.0 (s, 1H, Ar), 7.30 (t, J=6.9 Hz, 1H, Ar), 7.40
(dd, J=6.9, 7.1 Hz, 2H, Ar), 7.58 (d, J=7.1 Hz, 2H, Ar)

lH NMR(Toluene-d3): 5 0.62 (d, J=7.2 Hz, 3H, CH3CH), 1.7 (broad s, 1H, OH), 2.09 (s,
3H, CH3Ar), 2.21 (s, 3H, CH3Ar), 2.63, 3.58 (AB quartet, J=15.9 Hz, 2H, CH2), 3.18 (q,
J= 7.2 Hz, 1H, CHCH3), 6.90-7.5 (m, 7H, Ar)

IR(CC14): 3462, 3061.4, 2968.8, 1448, 1240.3, 912.4, 848.8, 700.25

195

 

hv +
o I. .
my", 1‘ Ph
C
A

H3 CH3 A

 

 

 

 

 

 

 

L

 

 

 

 

Y—r 1 v v v -—r i v 1 T v f *7 1 T fi' ' 1 v v i fi

7 6 s 4 3 2 1 ppm

Figure 39. 1H NMR Spectra of ot-Mesitylpropiophenone Before and After
Irradiation in Toluene 09290 nm)

196

Products from a—(2,4,6-Triisopropylphenyl)acetophenone ( 9)
a-(2,4,6-Triisopropylphenyl)propiophenone (0.005 g) in 0.8 mL of deuterated
benzene was irradiated through Pyrex filter. The signals for two products, an enol and an
indanol, were detected upon analysis of the NMR spectrum of the photolysis mixture.
The effect of temperature and phase on product ratios was also investigated by
conducting the photochemistry in acetone/ethanol, ice-water and silicon oil (110°C) baths
and in solid. A small amount of the other disproportionation product, 1-phenyl-2-(2-(2-
propenyl)-4,6-diisopropylphenyl)ethanol, was observed at 24°C and 90°C irradiations.
The enol indanol ratio was determined by NMR integration of the vinylic singlet signals
of the enols and the upfield methyl singlet signal of the indanol. In order to separate the
products, large scale irradiation using 0.40 g of 01—(2,4,6-triisopropylphenyl)
propiophenone in 100 mL of benzene was performed. Solvent was evaporated to leave a

yellow solid which was separated by PTLC using 3% ethyl acetate in hexane solution.

 

9ean 9alc

Scheme 69. Photoproducts of 01-(2,4,6-Triisopropylphenyl)acetophenone

'2'.
5'

5

Figure 40. 1H NMR of a-(2,4,6-Triisopropylphenyl)acetophenone After Irradiation

in Toluene (A > 290nm)

E

2

r1
Md!

 

197

 

 

 

 

 

lLA_LA111ALIJLLL11AL1ILJLLIAA

 

 

198

WWW

lH NMR(CDC13): 5 0.78 (s, 3H, CH3), 1.29 (d, J=7.3 Hz, 12H, 2 (CH3)2CH), 1.36 (s, 3H,
CH3), 2.14 (broad s, 1H, OH), 2.92 (septet, J= 7.2 Hz, 2H, 2CH(CH3)2), 3.08, 3.81 (AB
quartet, J= 16.1 Hz, 2H, CH2), 6.90 (s, 1H, Ar), 7.0 (s, 1H, Ar), 7.24-7.40 (m, 3H, Ar).
7.60 (d, J= 7 Hz, 2H, Ar)

lH NMR(Toluene-dg): 5 0.75 (s, 3H, CH3), 1.20 (d, J=7.2 Hz, 6H, 2 (CH3)2CH), 1.30 (d,
J=7.2 Hz, 12H, 2 (CH3)2CH), 1.35 (s, 3H, CH3), 2.80, 3.60 (AB quartet, J= 16.1 Hz, 2H,
CH2), 2.85 (septet, J= 7.2 Hz, 1H, CH(CH3)2), 3.30 (septet, J= 7.2 Hz, 2H, 2CH(CH3)2),
6.90 (s, 1H, Ar), 7.1 (s, 2H, Ar), 7.1-7.3 (m, 3H, Ar), 7.5 (d, J: 7 Hz, 2H, Ar)

l3C NMR(CDC13): 5 19.6, 22.9, 23.1, 24.2, 24.3, 28.1, 31.0, 34.4, 42.2, 51.6, 87.2, 118.4,
121.6, 126.6, 127.1, 127.7, 133.6, 141.8, 144.8, 148.4, 150.3

IR(neat): 3420, 3080,2850, 1494, 1384, 876.8 cm'1

1Z1-1-Phenyl-2j2,4,6-triisopropylphenyl)ethenol

lH NMR(Toluene-d3): 5 1.20 (d, J=7.2 Hz, 6H, 2 (CH3)2CH), 1.30 (d, J=7.2 Hz, 12H, 2
(CH3)2CH), 2.85 (septet, J= 7.2 Hz, 1H, CH(CH3)2), 3.30 (septet, J= 7.2 Hz, 2H,
2CH(CH3)2), 4.75 (broad s, 1H, OH), 6.1 (s, 1H, Vinyl), 7.0-7.2 (m, 3H, Ar), 7.2 (s, 2H,
Ar), 7.8 (d, 1= 7 Hz, 2H, Ar) I

lH NMR(Methanol-d4): 5 1.16 (d, J= 7.2 Hz, 6H, (CH3)2CH), 1.18 (d, J= 7.2 Hz, 6H,
(CH3)2CH), 1.24 (d, J: 7.2 Hz, 6H, (CH3)2CH), 2.85 (septet, J= 7.2 Hz, 2H, 2CH(CH3)2),
3.27 (septet, J: 7.2 Hz, 1H, CH(CH3)2), 5.91 (s, 1H, vinylic), 7.0 (s, 1H, Ar), 7.2-7.4 (m,

5H, Ar), 7.70 (d, 1: 7 Hz, 2H, Ar)

199

(E)-l-Phenyl-2-(2,4,6-triisopropylphenyl)ethenol

lH NMR(Toluene-d8): 5 1.10 (d, J=7.2 Hz, 6H, 2 (CH3)2CH), 1.18 (d, J=7.2 Hz, 12H, 2
(CH3)2CH), 2.85 (septet, J= 7.2 Hz, 1H, CH(CH3)2), 3.30 (septet, J= 7.2 Hz, 2H,
2CH(CH3)2), 4.75 (broad s, 1H, OH), 6.4 (s, 1H, Vinyl), 7.0 (s, 2H, Ar), 7.1-7.2 (m, 3H,
Ar), 7.7 (d, J= 7 Hz, 2H, Ar)

lH NMR(Methanol-d4): 5 0.88 (d, J: 7.2 Hz, 6H, (CH3)2CH), 1.08 (d, J= 7.2 Hz, 6H,
(CH3)2CH), 1.2 (d, J= 7.2 Hz, 6H, (CH3)2CH), 2.85 (septet, J= 7.2 Hz, 2H, 2CH(CH3)2),
3.27 (septet, J= 7.2 Hz, 1H, CH(CH3)2), 5.88 (s, 1H, vinylic), 6.90 (s, 1H, Ar), 7.2-7.4 (m,

5H, Ar), 7.65 (d, J= 7 Hz, 2H, Ar)

l-Phenyl-2-12-(2-propenyl)4,6-diisopropylp_henyl)ethanol

lH NMR(Toluene-d8): 5 1.15 (d, J=7.2 Hz, 3H, (CH3)2CH), 1.25 (d, J=7.2 Hz, 3H,
(CH3)2CH),1.3 (6H, t, J=7.2 Hz, 6H, (CH3)2CH), 1.6 (broad s, 1H, OH), 1.95 (s, 3H,
allylic CH3), 2.85 (septet, J= 7.2 Hz, 1H, CH(CH3)2), 3.1, 3.24 (2H, AB quartet of d, J=
8.4, 2.7, 5.4 Hz, 2H, CH2), 3.45 (septet, J= 7.2 Hz, 1H, CH(CH3)2), 4.79 (1H, dd, J= 2.7,
5.4 Hz, 1H, CHOH), 4.85 (d, J= 1.5 Hz, 1H, vinylic), 5.15 (d, J= 1.5 Hz, 1H, vinylic),
6.95 (s, 1H, Ar), 7.05 (s, 1H, Ar), 7.1-7.2 (m, 3H, Ar), 7.3 (2H, d, 1= 7 Hz, 2H, Ar)

IR(CC14): 3582.3, 2964, 2931.2, 1464.2, 1384.1, 1167, 1055.2, 901.8, 808.3, 738.8

Products from 1-Trimethylsiloxy-I-phenyl-2-(2 ’,4 ’,6 ’-triisopropylphenyl)ethene
Photochemical conversion of enol to indanol was checked by synthesis and

irradiation of trimethylsilyl enol ether of a-(2,4,6triisopropylphenyl)acetophenone. The

200

Z-enol ether was synthesized by treatment of ketone with KH and trimethylsilyl chloride.
Irradiation of this enol ether in benzene resulted in formation of the E-isomer but no

indanol or ketone.

 

—- hv —
OSiMea P“

 

1H NMR(C6D6): 5 -0.1 (s, 9H, Si(CH3)3), 1.3-1.5 (broad, 18H, 3 (CH3)2CH), 2.85 (septet,
J= 7.1 Hz, 1H, CH(CH3)2), 3.5 (septet, J=7.2 Hz, 2H, 2 CH(CH3)2), 6.5 (s, 1H, vinylic),
7.0-7.2 (m, 5H, Ar), 7.7 (d, J: 6.9 Hz, 2H, Ar)

l3C NMR(CDC13): 5 0.13, 24.21, 29.74, 30.55, 34.41, 107.28, 120.24, 125.43, 127.76,

128.24, 129.93, 147.28, 147.61, 149.33

E-l-Trimeth lsilox -l- hen 1-2- 2’ 4’ 6’-triiso ro 1 hen lethene

   

1
H NMR(C6D6): 5 0.0 (s, 9H, Si(CH3)3), 1.3-1.5 (broad, 18H, 3 (CH3)2CH), 2.85 (septet,
J: 7.1 Hz, 1H, CH(CH3)2), 3.5 (septet, J=7.2 Hz, 2H, 2CH(CH3)2), 6.7 (s, 1H, vinylic),

7.0-7.2 (m, 5H, Ar), 7.5 (d, J= 6.9 Hz, 2H, Ar)

201

Products from a—(2-Ethylphenyl)acetone (10)

a—(2-Ethy1phenyl)acetone (0.002 g) in 0.8 mL of deuterated benzene was
irradiated until starting material could not be observed by NMR. The signals for three
products were detected in the NMR spectrum of the mixture. These products included
two isomeric indanols and a diarylethane. The effect of temperature and phase on product
ratios was also investigated by conducting the photochemistry in acetone/ethanol, ice-
water and silicon oil (110°C) baths and in solid. The product ratios were determined by
NMR integration of the methyl doublet signals of the indanols and the methylene singlet
signal of the diarylethane. The structural assignments of the indanols was accomplished
by performing shift and nOe experiments. Addition of Rondeau’s reagent to 0.01 M
solution of each indanol in CDC13, caused an upfield shift of all proton signals. However,
the methine signal in the minor isomer moved upfield twice as much as the methyl signal,
while the upfield shifts of both methyl and methine signals in the major isomer were
comparable. Furthermore, irradiation of the methine signal in the minor isomer caused an
enhancement of the OH signal. These data strongly suggest that the minor isomer has an
E-stereochemistry. Large scale irradiation using 0.20 g of oc—(2-ethylphenyl)acetone in
150 mL of toluene was performed until 100% conversion (GC). Solvent was removed to
leave a yellow oil which was chromatographed by PTLC using 3% ethyl acetate in
hexane to separate the products. The Z-indanol was the first eluted isomer. The indanols

were recovered as oils.

202

 

10

Scheme 71. Photoproducts of a-(2-Ethylphenyl)acetone

Z-lg-Dimethyl-Z-indanol

lH NMR(CDC13): 5 1.28 (d, J=7.1 Hz, 3H, CH3CH), 1.45 (s, 3H, CH3), 2.93 (Half of an
AB quartet, J=16 Hz, 1H, CH2), 2.97 (q, J= 7.1 Hz, 1H, CHCH3), 3.02 (Half of an AB
quartet, J= 16 Hz, 1H, CH2), 7.13-7.23 (m, 4H, Ar)

lH NMR(C6D6): 5 1.12 (d, J=7.2 Hz, 3H, CH3CH), 1.2 (s, 3H, CH3), 1.6 (s, 1H, OH),
2.65 (q, J=7.2 Hz, 1H, CHCH3), 2.7 (AB quartet, J= 15.94 Hz. 2H, CH2), 7.0-7.15 (m,
4H, Ar)

lH NMR(Toluene-d8): 5 1.11 (d, J=7.2 Hz, 3H, CH3CH), 1.18 (s, 3H, CH3), 1.6 (s, 1H,
OH), 2.65 (q, J=7.2 Hz, 1H, CHCH3), 2.7 (AB quartet, J= 15.94 Hz, 2H, CH2), 7.0-7.15
(m, 4H, Ar)

l3C NMR(C6D6): 5 14.5, 25.4, 47.7, 49.3, 81.1, 124, 125.1, 126.8, 126.9, 141.2, 146.9

IR(CC14): 3580.4, 3072.9, 3024.7, 2966.9, 2934.1, 1460.3, 1246.2, 1157.4, 1072.6, 951,

775.4, 763.9, 740.7

203

 

 

 

 

 

Figure 41. 1H NMR of the Indanol Mixture from a-(2-Ethylphenyl)acetone in
Benzene

204

IH NMR(C6D6): 5 1.0 (d, J=7.2 Hz, 3H, CH3CH), 1.02 (s, 3H, CH3), 2.73 (AB quartet, J=
15.5 Hz, 2H, CH2), 2.88 (q, 1: 7.2 Hz, 1H, CHCH3), 7.0 (dd, J=2.4, 2.3 Hz, 1H, Ar), 7.03
(d, J=1.4 Hz, 1H, Ar), 7.05 (d, J=2.4 Hz, 1H, Ar), 7.09 (dd, J=2.3, 1.4 Hz, 1H, Ar)

lH NMR(Toluene-d8): 5 1.0 (d, J=7.2 Hz, 3H, CH3CH), 0.99 (s, 3H, CH3), 2.73 (AB
quartet, J= 15.5 Hz, 2H, CH2), 2.88 (q, J= 7.2 Hz, 1H, CHCH3), 7.0 (dd, J=2.4, 2.3 Hz,
1H, Ar), 7.03 (d, J=1.4 Hz, 1H, Ar), 7.05 (d, J=2.4 Hz, 1H, Ar), 7.09 (dd, J=2.3, 1.4 Hz,
1H, Ar)

lH NMR(CDC13): 5 1.19 (d, J=7.3 Hz, 3H, CH3CH), 1.30 (S, 3H, CH3), 2.96 (collapsed

AB quartet, 2H, CH2), 3.05 (q, J=7.2 Hz, 1H, CHCH,), 7.0—7.3 (m, 4H)

”C NMR(C6D6): 5 14.4, 22.6, 47.4, 50.9, 82.0, 123.9, 124.9, 126.8, 126.9, 127.9, 147.0

IR(CC14): 3431.8, 3072.9, 3024.9, 2964.7, 2932.2, 1255.8, 1145.8, 1032, 987.7, 927.9,

763.9, 740.7
Shift Reagent Experiments:

Addition of Rondeau’s reagent, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-
octandionato) praseodymium, to 0.01 M solution of each indanol in CDC13, caused the
following upfield shifts:

Z-lJ-Dimethyl-Z-indanol: methyl doublet signal at 1.30 ppm moved to 1.01 ppm,
methyl singlet signal at 1.47 ppm moved to 1.06 ppm, methine quartet signal at 2.97 ppm
moved to 2.68 ppm, and the AB quartet signals at 2.95 and 3.04 ppm moved to 2.54 and

2.74 ppm.

205

E-l,2-Dimethy1—2-indanol: methyl doublet signal at 1.18 ppm moved to 1.13 ppm,
methyl singlet signal at 1.27 ppm moved to 1.20 ppm, methine quartet signal at 3.05 ppm
move to 2.96 ppm, and the AB quartet signal at 2.96 ppm moved to 2.98 and 2.86 ppm.
Addition of tris(2,2,6,6-tetramethyl-3,5-heptandionato)europium reagent to the
mixture of indanols in CDC13 caused the following downfield shifts:
Z-lJ-Dimethyl—Z-indanol: methyl doublet signal at 1.30 ppm moved to 1.33 ppm,
methyl singlet signal at 1.47 ppm moved to 1.52 ppm. The other peaks could not be
identified due to peak broadening.
E-lJ-Dimethyl-Z-indanol: methyl doublet signal at 1.19 ppm moved to 1.23 ppm,
methyl singlet signal at 1.27 ppm moved to 1.34 ppm. The other peaks could not be

identified due to peak broadening.

NOe Experiments:

Z-lJ-Dimethyl-Z-indanol: Irradiation of the signal at 1.30 ppm (CDC13) caused the
following enhancements: 2.96-3.05 ppm (3%), 7.1-7 .3 ppm (3.1%)

Irradiation of the signal at 1.47 ppm caused the following enhancements: 2.96-3.05 ppm
(4%), 7.1-7.3 ppm (1.6%)

E-l,2-Dimethyl-2-indanol: Irradiation of the signal at 2.73 ppm (C6D6) caused the
following enhancements: 1.0-1.05 ppm (1.0%), 1.6 ppm (0.4%), 6.9-7.1 ppm (1.7 %)
Irradiation of the signal at 2.88 ppm caused the following enhancements: 1.0-1.05 (0.8%),

1.6ppm (0.6%), 6.9-7.1 ppm (2%)

206

lg-Dii2’-ethylphenyl)ethane

lH NMR(CDC13): 5 1.22 (t, J=7.5 Hz, 6H, 2CH3CH2), 2.67 (q, J= 7.6 Hz, 4H, 2CH2CH3),

2.8 (s, 4H, 2CH2). 7.1-7.2 (m, 8H, Ar)

”C NMR(CDC13): 5 15.4, 25.5, 34.3, 125.9, 126.3, 128.5, 129.1

Products from a—Mesitylacetone (11)

a-Mesitylacetone (0.002 g) in deuterated benzene was irradiated until starting
material could not be observed by NMR. Two products were detected in the NMR
spectrum of the mixture and were identified as an indanol and a diarylethane. The effect
of temperature and phase on product ratios was also investigated by conducting the
photochemistry in acetone/ethanol and silicon oil (110°C) baths and in solid. Product
ratios were determined by NMR integration of the methylene signals of the indanol (AB
quartet) and the diarylethane (singlet). Large scale irradiation using 0.20 g of or—
mesitylacetone in 100 mL of benzene was performed until 100% conversion by GC.
Solvent was removed to leave a yellow oil which was chromatographed by PTLC using
3% ethyl acetate in hexane to separate the products. The indanol was eluted after the

diarylethane and was recovered as an oil.

 

1 1 l lind 1 lcleav

Scheme 72. Photoproducts of ot-Mesitylacetone

207

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1.104

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Figure 42. 1H NMR of the Methyl Region of the Indanol Mixture from 01-(2-
Ethylphenyl)-acetone in Benzene

 

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Figure 43. 1H NMR of the Methylene Region of the Indanol Mixture from 01-(2-
Ethylpheny1)acetone in Benzene

209

lH NMR(C6D6): 5 1.30 (s, 3H, CH3), 2.05 (s, 3H, CH3Ar), 2.20 (s, 3H, CH3Ar), 2.65 (AB
quartet, J: 16.6 Hz, 2H, CH2), 2.80 (AB quartet, J: 16.5 Hz. 2H, CH2), 6.72 (s, 1H, Ar),
6.73 (s, 1H, Ar)

IH NMR(CDC13): 5 1.63 (s, 3H, CH3), 2.13 (s, 3H, CH3Ar), 2.33 (s, 3H, CH3Ar), 3.0
(Half of an AB quartet, J=16.6 Hz, 1H, CH2), 3.1 (Half of an AB quartet, J=16.5 Hz, 1H,
CH2), 3.25 (Half of an AB quartet, J= 16.6 Hz, 1H, CH2), 3.35 (Half of an AB quartet, J:
16.5 Hz, 1H, CH2), 6.79 (s, 1H, Ar), 6.81 (s, 1H, Ar)

l3C NMR(C6D6): 5 19.0, 21.3, 28.0, 47.0, 48.9, 79.3, 123.3, 128.5, 133.7, 136.1, 137.9,
141.9

IR(CCl4): 3443, 2968.8, 2926.4, 1469.9, 1448.7, 1230.7, 1076.4, 895, 873.8, 850.7, 702.2

LZL-Difimesitylethane
lH NMR(CDC13): 5 2.3 (s, 6H, 2CH3), 2.4 (12H, s, 4 CH3), 2.8 (s, 4H, 2CH2), 6.9 (s, 4H,
Ar)

13C NMR(CDC13): 5 20.1, 20.8, 28.9, 129.1, 135.2, 135.7, 136.3

Products from a—(2,4,6-Triethylphenyl)acetone (12)

a—(2,4,6-Triethylphenyl)acetone (0.004 g) in deuterated toluene was irradiated
until starting material could not be observed by NMR. The signals for several products
were detected in the NMR spectrum of the mixture. These products included two

isomeric indanols and a diarylethane. The peaks for the two isomeric indanols overlap

210

and separation is difficult. The Z-stereochemistry for the major indanol was based on the
comparison of the peaks to that of the Z-indanol of a—(2-ethylphenyl)acetone. Product
ratios were determined by NMR integration of methyl doublet signals of indanols and the
methylene singlet signal of the diarylethane. Large scale irradiation using 0.30 g of or-
(2,4,6-triethylphenyl)acetone in 100 mL of benzene was performed until 100%
conversion by GC. Solvent was removed to leave a yellow oil which was
chromatographed by PTLC using 5% ethyl acetate in hexane to separate the products.
The indanols had a lower rfvalue than the diarylethane which had moved with the solvent

line.

 

12 12indZ 12indE 12cleav

Scheme 73. Photoproducts of a-(2,4,6-Triethylphenyl)acetone

4 6-Dieth M Z -dimeth 1-2-indanol

lH NMR(C,D,): 5 1.12 (t, J= 7.5 Hz, 3H, CH3CH2). 1.19 (d, J: 7 Hz, 3H, CH3CH), 1.20
(t, J: 7.5 Hz, 3H, CH3CH2), 1.26 (s, 3H, CH3), 2.44 (q, J= 7.5 Hz, 2H, CHZCHg), 2.56 (q,
.1: 7.5 Hz, 2H, C CH2H3), 2.62 (Half ofAB quartet, J: 16 Hz, 1H, CH2), 2.72 (1H, q, 1:

7.5 Hz, 1H, CHCH3), 2.74 (Half of AB quartet, J= 16 Hz, 1H, CH2). 6.85 (s, 2H, Ar)

13
C NMR(C6D6): 5 11.6, 14.9, 16.5, 25.4, 26.8, 29.4, 45.6, 49.3, 80.9, 121.1, 125.9,

143.3, 146.9

211

IR(CC14): 3440, 2968, 2930, 1470, 1076.4, 895, 704.2

4 6—Dieth l-l -dimeth l-2-indanol

lH NMR(C6D6): 5 1.11 (d, J: 7.5 Hz, 3H, CH3CH), 1.13 (s, 3H, CH3). 1.15 (t, J=7.5 Hz,
3H, CH3CH2), 1.20 (t, J=7.5 Hz, 3H, CH3CH2), 2.43 (AB quartet, J: 14 Hz, 2H, CH2),
2.48 (q, J: 7.5 Hz, 2H, CH2CH3), 2.56 (q, J= 7.5 Hz, 1H, CHCH3), 2.62 (q, J= 7.5 Hz,

2H, CHZCH3). 6.81 (s, 1H, Ar), 7.05 (s, 1H, Ar)

l,2-Di(2,4,6-triethylphenyl)ethane

IH NMR(C,D,): 5 1.15 (t, J: 7.5 Hz, 12H, 4CH3CH2), 1.2 (t, J: 7.5 Hz, 6H, 2CH3CH2),
2.5 (q, 1: 7.5 Hz, 4H, CHZCH3), 2.7 (q, I: 7.5 Hz, 8H, 2CH2CH3), 2.85 (s, 4H, Ar), 6.9

(s, 4H, Ar)

Products from a—(2,4,6-Triisopropylphenyl)acetone (13)

01—(2,4,6-Triisopropylphenyl)acetone (0.005 g) in deuterated benzene was
irradiated. The signals for three products were detected in the NMR spectrum of the
mixture. One of these products, the enol, disappears as the irradiation time (percent
conversion) increases. The signals for two products were detected at 100% conversion in
the NMR spectrum of the photolysis mixture. These products included an indanol and a
diarylethane. The indanol/diarylethane ratio was determined by NMR integration of the
methyl singlet signal of the indanol and the methylene singlet signal of the diarylethane.
Large scale irradiation using 0.30 g of a—(2,4,6-triisopropylphenyl)acetone in 100 mL of

toluene was performed until 100% conversion (GC). Solvent was removed to leave a

212

yellow oil which was chromatographed by preparative scale tlc using hexane to separate

the products. The indanol was the second fraction eluted and was recovered as an oil.

. \ CH3 H H CH3
\ 1 / O hV .‘CHa + — CH
C D
6 6 H3O ”CH3

13 13ind 13enl 13cleav

 

 

Scheme 74. Photoproducts of 01-(2,4,6-Triisopropy1pheny1)acetone

4 6-Diiso ro 1-11 -trimeth l-2-indanol

lH NMR(CDC13): 5 1.10 (s, 3H, CH3), 1.25 (6H, t, J= 6.84 Hz, 6H, (CH3)2CH), 1.27 (d,
I: 6.84 Hz, 6H, (CH3)2CH), 1.30 (s, 3H, CH3), 1.36 (s, 3H, CH3), 1.8 (broad s, 1H, 0H),
2.8-3.0 (m, 2H, 2CH(CH3)2), 2.95, 2.99 (AB quartet, 1: 16 Hz, 2H, CH2), 6.88 (d, 1:
1.59 Hz, 1H, Ar), 6.95 (d, J= 1.59 Hz, 1H, Ar)

”C NMR(CDC1,); 5 19.9, 20.6, 22.6, 23.9, 26.1, 30.6, 33.9, 43.4, 49.4, 83.1, 117.8,
120.9, 133.6, 1442,1477, 150.6

IR(CC14): 3448, 2966, 2930, 1448.7, 1076, 802.4

1Ztl-Methyl-2-(2,4,6-triisopropylphenyl)ethenol

lH NMR(C6D6): 5 1.1-1.3 (d, J: 6.84 Hz, 18H, 3 (CH3)2CH), 1.8 (s, 3H, allylic CH3),
2.7-3.0 (3H, septet, .1: 6.84 Hz, 3H, 3CH(CH3)2), 4.4 (broad s, 1H, OH), 5.2 (s, 1H,

vinylic CH), 6.9 (s, 1H, Ar), 7.05 (s, 1H, Ar)

L1l+ll

AlAAIAPlLLLlAA

Zl0
h

 

Figure 44. 1H NMR of a-(2,4,6-Triisopropylphenyl)acetone after Irradiation in

 

213

 

 

’
O
O
E
r-o ‘
1 11
1-0 g:
I
1
t O
r E
+
a
O
I
l
. g}
+
a
I
M

Toluene (A > 290 nm, T= 297 K)

214

1,z-Dif2,4,6-triisopropylphenyl)ethane

lH NMR(CDC13): 5 1.20 (d, J= 6.84 Hz, 24H, 4 (CH3)2CH), 1.24 (d, J=6.84 Hz, 12H, 2
(CH3)2CH), 2.90 (s, 4H, 2CH2), 3.25 (septet, J= 6.84 Hz, 6H, 6CH(CH3)2), 6.98 (s, 4H,

Ar)

Products from o-ten-Buo’ltrifluroacetophenone (14)

o-tert-Butyltrifluroacetophenone (0.003 g) in 0.8 mL of deuterated benzene was
irradiated until no trace of starting material could be observed by NMR. The signals for
two products were detected upon analysis of the NMR spectrum of the photolysis
mixture. The products were identified to be an unsaturated alcohol and an indanol. The
product ratios were determined by NMR integration of the methyl singlet signal of the
alcohol and indanol. Products were separated by performing large scale irradiation using
0.30 g of o-tert-Butyltrifluroacetophenone in 100 mL of benzene. Solvent was evaporated
to leave a yellow oil which was chromatographed by PTLC using 30% ethyl acetate in

hexane solution. The indanol eluted before the unsaturated alcohol.

 

14 Mind 14alc

Scheme 75. Photoproducts of o-tert-Butyltrifluroacetophenone

215

1-{2’-(3-(2”-Methyl)propargyuphenylitriflouromethylethanol

lH NMR(CDC1,): 5 1.8 (s, 3H, allylic CH3), 2.42 (d, J= 4.88 Hz, 1H, 0H), 3.40 (AB
quartet, 1: 16.5 Hz, 2H, CH2), 4.5 (dq, J=1.4, 0.83 Hz, 1H, vinylic CH), 4.88 (dq, J=1.4,
1.5 Hz, 1H, vinylic CH), 5.3 (dq, J= 4.8, 6.7 Hz, 1H, CHOH), 7.2 (m, 1H, Ar), 7.35 (m,
2H, Ar), 7.65 (m, 1H, Ar)

”C NMR(CDC13): 5 22.3, 41.6, 69 (q, 1= 34 Hz), 112.5, 124.5 (q, J=290 Hz), 127,

127.4, 129, 131, 133, 138, 144.8

l9F NMR(CDC13): 5 -2.0 (d, J= 6.7 Hz, 3F, CF 3) reference: ethyl trifuroacetate

IR(CC14): 3618.9, 2937.9, 1453.5, 1272.2, 1169.1, 1132.4, 1061.9, 898.9, 803.4, 701.2

3,_3_-Dimethyl-l-trifluromethyl-l-indanol

lH NMR(CDC13): 5 1.37 (s, 3H, CH3), 1.42 (s, 3H, CH3), 2.20 (1H, q and half of an AB
quartet, J=1.16, 14.4 Hz, 1H, CH2), 2.45 (half of an AB quartet, J= 14.2 Hz, 1H, CH2),

7.0 (m, 1H, Ar), 7.35 (m, 2H, Ar), 7.55 (d, 1H, Ar)

Products from o-tert-Amylbenzophenone

o-tert-Amylbenzophenone 0.4 g in 100 mL of benzene was irradiated until no
trace of starting material could be observed by GC. The signals for two pairs of isomeric
indanols were detected upon analysis of the NMR spectrum of the photolysis mixture.
The products were separated by liquid chromatography using 5% ethyl acetate in hexane.

NOe experiments were performed to determine the stereochemistry of the isomers.

216

 

Scheme 76. Photoproducts of o-tert-Amylbenzophenone

E 2 -Trimeth l-l- hen l-l-indanol

 

lH NMR(CDC13): 5 0.82 (d, J= 7.3 Hz, 3H, CH3CH), 0.89 (s, 3H, CH3), 1.36 (s, 3H,
CH3), 2.41 (q. =7.3 Hz, 1H, CHCHs), 7.09 (m, 2H, Ar), 7.2-7.5 (m, 7H, Ar)
Noe(CDC13): Irradiation at 5 0.82 ppm produced the following enhancements 5 1.36 ppm

(2.5%), 5 2.4 ppm (2.5%), 5 7.2-7.5 ppm (3.8%)

(Z)-2,3_,§-Trimethyl-l-phenyl-1-indanol

IH NMR(CDC13): 5 1.01 (d, J= 7.3 Hz, 3H, CH,CH), 1.30 (s, 3H, CH3), 1.39 (s, 3H,
CH3), 2.22 (q, J=7.3 Hz, 1H, CHCH3), 6.98 (d, 1H, Ar), 7.2-7.5 (m, 8H, Ar)

Noe(CDC13): Irradiation at 5 1.01 ppm produced the following enhancements 5 2.22 ppm

(4.5%), and 5 1.39 ppm (2.5%)

(E)- 3-Met_1_1vl-3-e_tl_1yl-l-phenyl-l-indanol
lH NMR(CDC13): 5 0.96 (t, J= 7.4 Hz, 3H, CH3CH2), 1.27 (s, 3H, CH3), 1.80 (q, J=7.4

Hz, 2H, CHZCH3), 2.29-2.56 (AB quartet, J= 14.1 Hz, 2H, CH2), 7.07 (d, 1H, Ar), 7.2-7.5

(m, 8H, Ar)

217

Noe(CDCl3): Irradiation at 5 1.27 ppm produced the following enhancements 5 1.80 ppm

(1.7%), and 5 2.29 ppm (1.9%), and 5 7.07 ppm (2.9%)

(Z)- 3-Methvl-3-ethyl-l-phenyl-1-indanol

lH NMR(CDC13): 5 0.81 (t, J= 7.4 Hz, 3H, CH3CH2). 1.42 (s, 3H, CH3), 1.58-1.72 (m,
2H), 2.26-2.45 (AB quartet, J= 14.1 Hz, 2H, CH2), 7.01 (d, 1H, Ar), 7.2-7.5 (m, 8H, Ar)
Noe(CDC13): Irradiation at 5 1.42 ppm produced the following enhancements 5 2.26 ppm

(0.8%), and 5 2.56 ppm (0.9%), and 5 7.0 ppm (0.8%).

Products from 2 '-(2,3-Dirnethyl-2-butyl)benzophenone (I 5)
2'-(2,3-Dimethyl-2-buty1)benzophenone (0.004 g) in 0.8 mL of deuterated
benzene was irradiated until no trace of starting material could be observed by NMR. The
signals for four isomeric products were detected upon analysis of the NMR spectrum of
the photolysis mixture. The products were identified as indanols and an unsaturated
alcohol. The product ratios were determined by NMR integration of the methyl singlet
signals of indanols and the isopropyl doublet signal of the alcohol. The effect of
temperature and phase on product ratios was also investigated by conducting the
photochemistry in acetone/ethanol, ice-water and silicon oil (110°C) baths and in solid.
The products were difficult to isolate because of a rapid dehydration on silica gel. The

spectroscopic data given are from the NMR mixtures of photoproducts in benzene.

218

   

15 lSindmZ

lSinde

 

15alc

Scheme 77. Photoproducts of 2-(2'-(2',3'-Dimethyl)butyl)benzophenone

Z-3-lsopropyl-3-methyl-lphenyl-1-indanol

1H NMR(C6D6): 5 0.62 (d, .1: 6.84 Hz, 3H, (CH3)2CH), 0.78 (d, J= 6.84 Hz, 3H,
(CH3)2CH), 1.40 (s, 3H, CH3), 1.91 (septet, J= 6.8 Hz, 1H, CH(CH3)2), 2.05 (Half of an
AB quartet, J= 14.1 Hz, 1H, CH2), 2.38 (Half of an AB quartet, J= 14.1 Hz, 1H, CH2),

6.8-7.2 (m, 7H, Ar), 7.5 (d, J=6.9 Hz, 2H, Ar)

E-3-lsopropyl-3-methyl-lphenyl-1-indanol

1H NMR(C,D,): 5 0.76 (d, J: 6.81 Hz, 3H, (CH3)2CH), 0.85 (d, I: 6.78 Hz, 3H,
(CI-13)2CH), 1.10 (s, 3H, CH3), 1.91 (septet, J: 6.8 Hz, 1H, CH(CH3)2), 2.08 (Half of an
AB quartet, J= 14.5 Hz, 1H, CH2), 2.58 (Half of an AB quartet, J= 14.5 Hz, 1H, CH2),

6.8-7.2 (m, 7H, Ar), 7.4 (d, J=6.9 Hz, 2H, Ar)

219

3,3,4,4-tetramethyl-lphenyl-1-indanol
lH NMR(C6D6): 5 1.11 (s, 3H, CH3). 1.16 (s, 3H, CH3). 1.18 (s, 3H, CH3). 1.45 (s, 3H,

CH3), 6.8-7.3 (m, 9H, Ar)

1- 2’- 3- 2”-Iso r0 1 r0 a l hen lbe lalcohol

IH NMR(C6D6): 5 0.92 (d, J= 6.96 Hz, 3H, (CH3)2CH), 0.95 (d, J= 6.85 Hz, 3H,
(CH3)2CH), 1.91 (septet, J= 6.8 Hz, 1H, CH(CH3)2), 3.26 (Collapsed AB quartet, J= 1.14
Hz, 2H, CH2), 4.47 (dd, J=1.53 Hz, 1H, vinylic CH), 4.84 (m, 1H, vinylic CH), 5.92 (s,

1H, CHOH), 6.8—7.2 (m, 7H, Ar), 7.4 (d, J=6.9 Hz, 2H, Ar)

3-Iso ro l-3-meth l-l- hen lindene
lH NMR(C6D6): 5 0.64 (d, J= 6.75 Hz, 3H, (CH3)2CH), 0.94 (d, J= 6.81 Hz, 3H,
(CH3)2CH), 1.25 (s, 3H, CH3). 1.97 (septet, J= 6.8 Hz, 1H, CH(CH3)2), 6.22 (s, 1H,

vinylic CH), 7.15-7.30 (m, 6H, Ar), 7.5 (m, 1H, Ar), 7.5 (d, J=6.8 Hz, 2H, Ar)

D. Quantitative Measurements

I. Semiempirical and Molecular Mechanics Calculations

All calculations were performed on a 7100/80 Power Macintosh computer
equiped with the Cache program. MOPAC, a version of MOPAC6 written by James J. P.
Stewartl '2 , was used for semiempirical calculations. The calculations were generally
done by creating a structural input which was minimized first by molecuar mechanics and
then by semiempirical calculations at AMI level of theory. The purpose of this. procedure

was to provide MOPAC with a better input structure.

 

220

Global minimizations (semiempirical-AMI) with dihedral drivers around bonds a
and b were performed on the minimized structures to obtain the conformations of other

minima.

R2
a

R1= Me, Et, i-Pr, CHzPh
R2=H, Me, Et, i-Pr

R3: H, MC

R4: Ph, Me

Figure 45

For R1=Et and CHzPh only conformations with the methyl and phenyl trans to the
hemipinacol radical moiety were considered, since the syn isomer was found to lie 4
kcal/mole above the trans. The lowest energy rotational maps for interconversion of
various minima were constructed by locating the lowest energy path between the minima
in the global minimization maps, minimizing the geometries in the path (semiempirical-
AMI) and plotting the energies. The details of global minimizations for all compounds
studied are listed in Tables 28 and 29. Tables 30-38 contain energies from double
dihedral minimizations about bonds a and b (Figure 45), calculated by MOPAC, for

several compounds.

Table 28. Details of Global Minimizations for Compounds 1-9

221

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Compound State Calculation Level # of Increments Key
Drivers' Words°

1 Ground Semiempirical AM] 2 36°, 36° NOANCI
GEO-OK

l Triplet Br. Semiempirical AMI-UHF 2 10°, 10° //

2 Ground Mechanics MM2 2 36°, 36° //

2 Triplet Br. Semiempirical AMl-UHF 2 20°, 20° //

3 Triplet Br. Semiempirical AMl-UHF 2 24°, 24° //

4 Ground Semiempirical AMl 2 10°, 10° //

4 Triplet Br. Semiempirical AMI-UHF 2 36°, 36° //

5 Ground Semiempirical AM] 2 15°, 15° //

5 Triplet Br. Semiempirical AMl-UHF 2 30°, 30° //

6 Ground Semiempirical AM] 2 36°, 36° //

6 Triplet Br. Semiempirical AMl-UHF 2 15°, 15° //

7 Ground Mechanics MM2 2 36°, 36° //

8 Ground Semiempirical AM] 2 36°, 10° //

8 Triplet Br. Semiempirical AMl-UHF 2 22°, 22° //

9 Triplet Br. Semiempirical AMI-UHF 2 15°, 15° //

 

 

 

 

 

 

 

 

a) Dihedral rotations about bonds a and b, respectively. b) NOANCI= no analytical
configuration interaction was used, GEO-OK= will allow the calculation to continue if a
high energy (non convergent) geometry is reached.

222

Table 29. Details of Global Minimizations for Compounds 10-15

 

 

 

 

 

 

 

 

 

 

Compound State Calculation Level # of Drivers' Increments Key
Words°
10 Ground Semiempirical AM] 2 16°, 16° NOANCl
GEO-OK
10 Triplet Br. Semiempirical AMl-UHF 2 30°, 30° //
11 Ground Mechanics MM2 2 36°, 36° //
12 Ground Mechanics MM2 2 36°, 36° //
12 Triplet Br. Semiempirical AMl-UHF 2 36°, 36° //
13 Triplet Br. Semiempirical AMI-UHF 2 15°, 30° //
14 Ground Mechanics MM2 1 10° //
1 1 5 Ground Semiempirical AM 1 -UHF 1 36° //

 

 

 

 

 

 

 

 

a) Dihedral rotations about bonds a and b, respectively. b) NOANCI= no analytical
configuration interaction was used, GEO-OK= will allow the calculation to continue if a
high energy (non convergent) geometry is reached.

 

223

Table 30. Grid of Energies (Real/mole) for The Ground State Optimization of or-(2-
Ethylphenyl)acetophenone

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

N“ 0° 36° 72° 108° 144° 180° 216° 252° 288° 324° 360°

1
0° 2.79 3.32 2.66 3.36 6.01 6.9 5.4 2.54 2.35 2.67 1.75
36° 1.4 2.04 2.03 1.13 4.4 7.31 6.48 2.14 1.62 2.71 1.44
72° 2.94 3.89 2.9 2.76 6.74 8.94 8.37 4.98 3.02 2.69 2.20
108° 2.53 2.88 2.44 3.03 6.27 8.08 7.39 4.59 2.51 2.88 2.52
144° 5.67 4.81 5.53 5.74 8 12.62 14.38 8.78 4.77 6.31 5.66
180° 5.56 6.94 6.98 8.22 12.83 17.55 12.32 6.71 6.53 7.13 6.84
216° 3.66 5.11 3.92 6.89 14.47 12.13 7.84 3.88 4.45 3.84 3.67
252° 1.89 2.13 2.07 5.14 7.53 8.53 5.74 2.49 1.65 2.31 1.90
288° 2.44 2.94 3.11 2.09 5.86 7.94 7.1 2.58 2.53 3.61 2.45
324° 3.02 4.18 4.24 3.87 7.54 8.76 5.88 2.8 3.62 3.56 3.03
360° 3.02 3.07 1.91 2.63 5.26 6.9 5.38 2.56 1.89 2.33 1.75

 

 

AMI NOMM MULLIK BONDS NOINTER PRECISE DENOUT ISOTOPE NODIIS

NOANCI GEO-OK, oetpapsm, Optimized search (grid) TOTAL CPU TIME IN FLEPO
: 89056.987

224

Table 31. Grid of Energies (Real/mole) for Global Minimization of The Triplet

Biradical of or-(2,4,6-Triethy1phenyl)acetophenone

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

N__. 0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330° 360°

1
0° 19.35 13.7 10.98 12.1 18.43 28.69 29.16 20.17 13.5 10.73 12.44 17.36 24.72
30° 9.71 8.18 8.85 13.37 22.22 22.28 17.12 12.42 9.5 10.64 18.93 14.3 9.83
60° 5.95 ' 6.25 7.17 11.83 17.83 13.64 11.14 9.41 8.67 10.31 15.08 7.47 5.94
90° 5.42 5.35 6.25 12.63 10.1 1 9.71 10.08 13.78 12.86 10.67 5.9 5.22 5.25
120° 6.78 9.35 1 1.63 1 1.27 8.1 9.77 12.76 16.92 20.25 20.17 17.62 6.65 6.61
150° 11.79 16.94 17.49 11.35 10.37 13.99 33.52 28.03 19.34 14.37 9.64 9.06 11.65
180° 18.1 23.15 13.47 11.19 12.81 18.77 25.72 29.84 12.87 11.46 12.01 15.31 20.21
210° 13.96 11.51 11.12 13.92 20.14 22.81 17.71 12.12 8.71 10.96 14.64 21.14 24.37
240° 9.91 8.89 8.71 11.33 15.96 15.22 1 1.64 8.43 7.73 9.34 l 1.89 12.24 9.79!
270° 8.25 8.25 9.69 11.59 1 1.24 10.84 9.72 9.69 10.54 9.43 9.31 8.7 8.21
300° 9.06 11.17 10.89 8.26 7.81 8.57 10.6 12.77 15.75 17.81 9.5 9.3 9.43
330° 12.4 16.22 13.6 9.34 8.53 11.09 17.25 22.35 22.37 14.98 11.32 11.32 13.6
360° 17.84 19.76 13.49 9.76 1 1.32 16.75 24.15 29.94 16.23 11.89 11.82 13.97 17.86

 

 

 

UHF TRIPLET AMI NOMM MULLIK BONDS NOINTER DENOUT ISOTOPE
NOANCI, GEO-OK, tetpap.br, Optimized search (grid), TOTAL CPU TIME IN FLEPO
: 63458.344

225

Table 32. Grid of Energies (kcal/mole) for Global Minimization of The Triplet

Biradical of a-(Z-Tolyl)propiopbenone

 

IN

00

240

48°

72°

96°

120°

144°

168°

192°

216°

240°

264°

288°

312°

336°

360°

 

00

35115

41.78

331

32111

1252

29113

32313

21153

4128

34111

2911

22124

2R158

27219

21182

35111

 

24°

.1287

31:48

30111

281N3

271"

29127

36117

21187

21196

2815

2R556

25141

2513

2715

3012

21183

 

430

32121

31.52

3017’

28112

21154

29117

21222

38J6»

1586

22176

26(17

251"

2613

22176

28317

28155

 

72°

33111

.3188

21158

21108

31.16

.3108

21145

30113

23109

301"

281MB

26115

26151

271Mi

22187

28155

 

96°

.1246

32115

3126

21185

27117

2154

2813

30317

32115

32315

3135

29115

27.17

273”

22175

2866

 

120°

21186

352”

21108

21193

2132

26115

22108

29113

1257

38117

21565

31.83

281MB

28112

28312

29117

 

1440

21163

38131

14188

34121

29113

28314

30121

34111

38115

4333

4M183

1556

31.72

21153

3133

3313

 

168°

46111

413”

21103

21168

31.56

321KB

35112

15109

41196

4217

36117

.1286

23167

32131

34131

 

39'

 

192°

21167

36114

21184

1256

32315

3554

21165

451”

50113

1167

23163

21132

32127

34(75

38123

4285'

 

216°

32117

.1288

32117

333”

.1176

14184

21165

2H578

331”

29315

28

22198

3013

3415

1179

.1249

 

2400

29315

311"

3142

31.93

3234

35

37327

38111

363N5

273”

2638

2126

281”!

21155

21139

291”

 

264°

34313

3312

3124

3139

21153

333”

21278

341”

3213

32117

3011

29113

2815

29113

21108

30327

 

288°

36111

21559

21155

32117

3131

31.76

33111

1144

21183

1178

3513

21587

21182

23162

.3198

3312

 

312°

39111

21158

21143

33373

.3147

31.33

21253

3415

3613

21186

36113

21142

.1249

21123

21168

1526

 

336°

43377

43113

4311

21187

21158

21176

.1256

36117

4N156

11142

35117

3233

311”

3196

1292

 

36m39

 

360°

 

 

21109

 

34m43

 

321M

 

3033

 

2848

 

29L"?

 

3151

 

21585

 

361%)

 

1258

 

291

 

28Jéi

 

28J€i

 

28113

 

31.78

 

3532

 

UHF TRIPLET AMI NOMM MULLIK BONDS NOINTER DENOUT ISOTOPE
NOANCI, GEO-OK, otolpp.br, Optimized search (grid), TOTAL CPU TIME IN FLEPO
: 53680.500

226

Table 33. Grid of Energies (Real/mole) for Global Minimization of The Triplet
Biradical of a-(2-Ethylphenyl)propiophenone

 

Kfi 0° 360 720 108° 144° 180° 216° 252° 2880 3240 3600

1

 

0° 29.23 24.02 22.74 22.91 22.9 30 24.43 18.35 16.62 18.91 29.31

 

36° 22.62 19.57 18.66 19.71 26.35 22.82 19.03 15.9 16.47 23.63 19.72

 

72° 17.76 19.89 20.7 20.66 23.09 23.23 21.64 18.23 17.44 16.64 17.23

 

1080 21.99 23.81 22.06 18.43 18.17 26.78 28.39 23.73 17.11 15.40 16.89

 

144° 22.02 34.78 28.83 20.61 21.52 28.37 38.29 29.64 20.56 18.33 22.0

 

180° 34.28 25.93 23.64 23.57 29.3 38.89 30.55 22.21 20.89 22.37 32.54

 

216° 23.73 21.27 22.75 28.39 36.5 27.13 21.05 18.2 23.85 27.95 21.35

 

252° 21.29 20.32 27.03 27.97 24.99 21.83 19.72 17.94 20.28 18.60 17.71

 

288° 24.82 26.59 25.15 24.31 23.42 24.66 26.58 28.43 20.28 19.44 21.34

 

324° 32.69 37.11 27.14 23.57 25.02 29.32 35.17 26.89 22.66 22.01 26.24

 

 

360° 29.24 24.07 22.94 22.92 23.03 29.91 24.34 18.71 16.72 18.8 29.4

UHF TRIPLET AMI NOMM MULLIK BONDS NOINTER DENOUT ISOTOPE
NOANCI, GEO-OK, oethylphenpph.br2, Optimized search (grid), TOTAL CPU TIME
IN FLEPO : 34510.688

 

 

 

 

 

 

 

 

 

 

 

 

 

227

Table 34. Grid of Energies (Real/mole) for Global Minimization of The Triplet
Biradical of a-(2,4,6-Trietbylpbeny1)propiopbenone

 

Y__ 00 300 60° 900 1200 150° 180° 2100 2400 2700 3000 330° 360°

1

 

0° 22.31 34.49 17.39 15.23 17.41 23.88 32.96 28.28 18.88 13.67 13.44 17.5 24.33

 

30° 13.7 13.67 13.65 15.52 20.05 22.05 16.78 11.52 7.91 9.9 15.27 23.57 20.28

 

60° 11.35 12.57 13.04 14.36 17.88 20.4 12.29 9.33 7.75 8.92 12.48 12.02 10.83

 

90° 15.11 15.47 16.09 14.46 12.75 12.76 13.9 15.35 14.39 11.69 10.92 10.62 12.19

 

1200 21.68 24.25 20.57 15.36 13.62 14.05 17.98 22.58 25.76 25.67 15.22 15.2 17.14

 

150° 21.17 29.54 23.32 16.91 14.93 17.75 24.47 33.96 28.58 21.09 17.02 17.18 21.31

 

1800 22.84 28.75 22.13 20.13 15.41 21.41 28.32 33.84 24.95 17.01 15.21 17.74 22.92

 

210° 13.49 13.21 13.42 15.25 18.8 21 16.48 11.19 7.74 8.44 14.43 19.57 25.45

 

240° 9.95 11.34 11.37 12.23 15.83 18.2 18.03 9.01 7.37 9.24 13.3 11.41 9.84

 

270° 11.68 15.08 15.4 13.91 12.82 12.38 12.78 15.82 14.45 12.2 11.85 10.67 11.15

 

300° 15.04 19.72 20.27 19.21 12.91 13.07 16.12 19.97 24.2 17.87 13.9 13.91 15.12

 

330° 24.02 32.09 24.36 18.78 16.91 20.3 26.98 38.33 29.45 22.87 19.94 20.11 24.21

 

 

360° 36.07 21.86 19.75 17.28 15.51 21.38 29.84 24.63 17.14 12.63 12.82 16.36 22.91

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UHF TRIPLET AMI NOMM MULLIK BONDS NOINTER DENOUT ISOTOPE
GEO-OK, tetpph.br, Optimized search (grid), TOTAL CPU TIME IN FLEPO :
74793.797

228

Table 35. Grid of Energies (Real/mole) for Global Minimization of The Triplet

Biradical of a-Mesitylpropiopbenone

 

N

00

240

48°

720

960

1200

1680

1920

2160

2400

2640

2880

3120

336°

360o

 

00

2587

25527

2129

2937

1163

1935

35512

325%?

22195

24517

222M

235¥1

25357

2N129

36Jh1

2196

 

240

26557

22123

28514

29312

3181

32J13

2937

2151

22196

22185

22J4

21196

25u15

273”

26553

21595

 

48°

2N585

26517

21J7

275?

295%5

275"

26314

25313

255KB

24J1

23527

24527

25378

25337

24591

22189

 

72o

2H119

21189

29317

2137

26

265”

22153

295KB

305“

2E182

285“

25354

24521

2141

255M!

2N528

 

960

35J3

33.18

2M148

27J8

26524

26324

285KB

IN172

21167

36J6>

21105

2N159

22198

22125

2737

29553

 

120O

lH155

21119

32513

295y1

285¥1

28JM5

3L8

2M526

4“178

14185

21164

1122

2M138

295M

2fl184

33J4

 

1440

11183

3835

21185

2N188

28314

2N133

21183

l“106

11194

44577

383%?

1128

2M176

3052

3171

36J5

 

1680

1157

3L27

295%?

28314

3138

413”

43J

2%198

3538

2M164

2179

22165

22198

293KB

33.17

2fl155

 

1920

28557

2136

28J

29J7’

32557

2M528

4132

41566

2737

24¢33

2131

22108

27J6

3036

3129

291x)

 

2160

2652

26JMS

265”!

28J9

1125

3L82

2931

2639

216

2L36

2L03

2121

2451

27

2597

25J

 

2400

2554

2592

SM528

2M582

2956

3114

3L77

2N165

2156

21105

2236

2353

2523

2503

25J1

2133

 

2640

28317

29AMZ

22198

22144

2126

22105

2123

27J2

28A”?

2933

265%?

24313

22162

2142

2189

2559

 

288°

21163

3216

29Jt3

275¥1

26J9

27x1

295IZ

3144

3103

21172

21592

29313

22125

2630

2123

285M5

 

312O

4L45

38J2

1193

2859

275?

2856

3L4

3527

395“

45315

3933

1109

3L63

295MB

2M138

32315

 

3360

4539

40J2

1578

.1187

21167

1191

21184

46J

52313

45J7

3133

3172

2959

295%?

3146

3554

 

 

360°

 

3432

 

3038

 

22196

 

2139

 

21162

 

1199

 

383K!

1591

 

 

21163

 

33.11

 

2836

 

21585

 

265K!

 

28J1

 

21108

 

365M

 

 

UHF TRIPLET AMI NOMM MULLIK BONDS NOINTER DENOUT ISOTOPE
NOANCI GEO-OK, mespph.br, Optimized search (grid), TOTAL CPU TIME IN FLEPO
: 70180.500

229

Table 36.Grid of Energies (Real/mole) for Global Minimization of The Triplet
Biradical of a-(2-Ethy1pheny1)acetone

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

N 00 300 60° 900 1200 150° 1800 2100 2400 2700 3000 330° 360°
1

00 -6.08 -9.62 40.68 41.47 41.43 -7.72 4.06 5.84 41.51 41.49 40.69 -9.66 -6.09
300 40.49 41.37 40.9 41.99 2.82 4.28 -5.97 -9.65 -11.63 41.73 -9.89 .654 -IO.61
60° 42 41.49 40.83 -11.76 -7.98 .051 4.49 -8.89 40.8 41.5 -9.08 40.15 42.08
900 -ll.46 40.67 40.19 40.86 -8.87 -7.8 -723 .497 -944 40.95 .991 41.14 -11.86
1200 40.4 -8.42 -947 40.66 40.6 -8.57 .557 -0.45 -7.86 40.34 -9.89 -10.61 40.4
1500 -7.52 -6.49 -9.21 40.36 40.03 -6.88 4.96 -0.84 -8.12 40.3 -9.41 -9.52 -7.49
1800 -6.03 -771 -9.36 40.39 -9.46 -3.79 3.55 6.95 .921 40.33 -941 -773 ~6.05
2100 .749 -954 -97 40.17 -8.16 5.25 -0.6 -6.95 40.46 40.36 -8.98 -6.6 .753
2400 40.52 40.48 -9.87 40.45 -7.86 4.56 1.63 -8.59 40.47 40.44 -93 -8.44 40.52
2700 41.8 41 40.22 40.92 -9.04 -5.86 .727 -754 -8.77 40.77 -9.66 40.64 -11.61
3000 41.99 40.19 -9.16 -ll.67 40.83 -8.93 .753 -5.62 -3.62 41.75 40.78 41.45 42.04
3300 -919 -8.02 -8.73 -912 -9.03 -6.57 -307 -2.99 40.13 41.93 40.69 41.52 40.6
360° -7.28 -7.96 ~8.26 -8.8 -8.23 -4.56 0.81 4.79 -8.25 -8.66 -8.18 -8.14 -6.92
UHF TRIPLET AMI NOMM MULLIK BONDS NOINTER DENOUT ISOTOPE

NOANCI GEO-OK, oetphacetone.br2, Optimized search (grid), TOTAL CPU TIME IN
FLEPO : 17316.492

230

Table 37. Grid of Energies (kcal/mole) for Global Minimization of The Singlet
Biradical of a-(2-Ethylphenyl)acetone

 

N

30°

120°

150°

180°

210°

240°

270°

300o

330°

360°

 

00

84.75

80.21

74.28

69.84

69.59

83.53

51.6

56.39

74.57

100.04

143.77

123.75

130.76

 

30°

83.73

92.96

109.3

107.29

108.21

96.28

113.29

86.86

77.56

78.54

87.65

111.12

107.14

 

60°

84.84

82.12

77.17

83.49

97.35

127.45

105.15

99.79

94.44

91.99

85.78

88.07

84.53

 

90°

87.05

85.14

80.65

77.18

75.48

83.91

87.53

87.86

97.67

97.43

85.36

87.8

86.3

 

120°

87.56

89.01

85.75

80.54

81.42

78.39

89.63

99.53

110.11

1 12.63

102.11

93.76

88.37

 

1500

96.63

94.05

84.07

89.93

102.76

108.62

105.88

147.2

121.69

88.6

86.18

89.06

95.13

 

1 80°

95.34

92.36

86.14

79.26

85.8

99.38

107.6

123.11

133.15

119.12

94.12

93.93

93.32

 

2100

105.77

95.69

94

104.8

115.46

118.36

92.43

102.12

79.9

81.16

86.16

87.91

95.35

 

240°

88.58

88.05

86.28

90.04

84.66

113.9

140.77

96.78

90.46

90.92

84.59

90.04

87.51

 

270°

92.73

94.96

99.74

99.58

91.79

82.07

84.8

80.67

70.65

74.12

81.95

84.65

84.93

 

3000

97.15

96.1

89.73

90.5

92.73

93.01

94.19

80.51

71.51

78

82.75

83.55

88.73

 

330°

96.13

97.2

88.89

89.17

104.09

148.62

129.76

96.37

71.62

75.57

78.77

81.82

88.06

 

 

360°

 

94.8

 

87.56

 

81.07

 

77.98

 

89.53

 

109.86

 

94.75

 

84.2

 

77.14

 

77.29

 

80.06

 

93.46

 

109.97

 

 

 

EXCITED SINGLET AMI NOMM MULLIK BONDS NOINTER DENOUT NOANCI
GEO-OK, oetphacetonebr, Optimized search (grid), TOTAL CPU TIME IN FLEPO :
54177.381

231

Table 38. Grid of Energies (Real/mole) for Global Minimization of The Triplet
Biradical of a-(2,4,6-Triisopropylphenyl)acetone

 

 

 

 

 

 

 

 

 

by 0° 30° 60° 90° 120° 1 50° 1 80° 2 1 0° 240° 270° 300° 3 30° 360°
1
~900 ~25.42 ~27.17 ~27.2 ~24.75 ~20.51 ~19.57 ~26.96 ~28.86 ~28.33 ~26.21 ~2 I .45 ~22.32 ~25.22
~60° ~26.82 ~27.68 ~27.84 ~24.19 ~24.59 ~27 ~28.55 ~29.28 ~28.8 ~26.97 ~23.43 ~24.52 ~26.97
~30° ~27.34 ~27.62 ~27.57 ~26.95 ~26. 18 ~28.51 ~28.75 ~28.97 ~28.33 ~27.38 ~25.93 ~26.46 ~27.25
0° ~26.66 ~27.09 ~26.92 ~27.34 ~27.69 ~28.52 ~28. 17 ~28.68 ~28.84 ~27.73 ~27.09 ~26.69 ~26.95
30° ~26.49 ~26.15 ~25.97 ~26.91 ~27.68 ~27.9 -27.53 ~27.99 ~27.71 ~27.97 ~26.84 ~26.52 ~26.46
60° ~26.01 ~23.61 ~23.88 ~25.68 ~26.28 ~27.1 ~26.99 ~26.19 ~24.66 ~25.46 ~25.46 ~26.34 ~25.88
90° ~24.42 ~22.26 ~20.07 ~23.49 ~25.14 ~26.37 ~25.47 ~23.46 ~22.09 ~22.57 ~24.26 ~25.46 ~24.29

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UHF TRIPLET AMI RESTART NOMM MU LLIK BONDS NOINTER DENOUT

NOANCI GEO-OK, tippacetone.br, Optimized search (grid), TOTAL CPU TIME IN
FLEPO : 81761.70]

2. Quantum Yield Measurements

Quantum yields for product formation were measured by irradiating solutions of
desired precursor parallel to 0.1 M valerophenone samples in sealed, degassed tubes.
Quantum yields were calculated from the following equation,

<D==[P]/l

232

where [P] is the concentration of photoproducts and I is the intensity of light absorbed by
samples.

The intensity of light, I, was determined by 0.10 M valerophenone actinometer irradiated
parallel with the samples to be analyzed. The irradiation was stopped after less than 10%
conversion and the valerophenone sample was analyzed for presence of acetophenone.
Acetophenone's concentration was, then, determined from Equation 6:

[AP]= fo [Std] x A P/AStd

A

Equation 6

where [AP] is the concentration of acetophenone, Rf is the instrument response factor for
acetophenone, A AP is the integrated area for acetophenone, [Std] is the concentration of
standard, and AStd is the integrated area for the internal standard. The intensity of the
light, I, can then be calculated using the acetophenone concentration based on (D49: 0.33,
thus,
I= [AP]/0.33 ~
The concentration of photoproduct, [P], can be calculated using Equation 7.
[P]= RflP) x [Std] x AP/AStd

Equation 7

Where R11?) is the instrument response factor for the product and AP is the integrated area

for the photoproduct. The instrumental response factors for photoproducts were obtained

using Equation 8:

 

233
Rap)=( [P]/[Std] )x ( As‘d/ AP )
Equation 8

In cases where the photoproducts are difficult to isolate or unstable to analyze, the

response factors can be calculated using Equation 9:

R.F.= {# of Carbons + 1/2 ( # of C-O bonds)Sui /{ # of Carbons + 1/2 ( # of C-0 bonds) }P

Equation 9

3. Quenching Studies

Stern-Volmer quenching studies were performed by irradiating sealed degassed
tubes containing the precursor and various amounts of quencher. The quenching is
assumed to be diffusion-controlled with a rate constant of 6x109 M'ls".3o The
experimental results measure the quenching of triplet to biradical. Thus in order to
translate this into triplet lifetime, it must be assumed that the predominant mode of triplet
relaxation is its conversion to the biradical. The results of these experiments are

summerized below.

 

234

Quantum Yield Measurement for 01;]2-Ethylphenyl[acetophenone in Benzene

Table 39. Product Quantum Yields of a-(2-Ethylphenyl)acetophenone in Benzene

GC analysis: 1400 Varian GC

DB~225 Megabore column

Initial column temp.: 100°C

Initial col. hold time: 2 min.

Final col. temp.: 160°C

Rate: 6°C/min., Hold time: 2 min.

 

 

 

 

 

 

 

 

 

Photoproduct A(product) A(std.) Concentration (D
Indanols 9.81939 29.23396 0.0015 0.47
Indanols 9.72419 29.94644 0.0014 - 0.46
Indanols 10.86830 29.26621 0.0016 0.50
Indanols 9.93122 29.79142 0.0015 0.47
Indanols 10.00819 29.49707 0.0015 0.48
Indanols 9.70557 29.39158 0.0015 0.46
Indanols 9.72804 29.24990 0.001 5 0.47

 

 

 

 

 

[Ketone]= 0.0239 M, [VP]= 0.1456 M, [C20]= 0.00328 M, 7»: 313 nm

Rf'"da"°'s=l .36, RfAP=2.90, Irradiation Time=2 hrs., Source= Mercury Arc Lamp

 

 

235

GC analysis: 1400 Varian GC

DB-225 Megabore column

Initial column temp.: 100°C

Initial col. hold time: 2 min.

Final col. temp.: 172°C

Rate: 8°C/min., Hold time: 5 min

Quantum Yield Measurement for aj2,4,6-Triethylphenyl[acetophenone in Benzene

Table 40. Product Quantum Yields of a-(Z,4,6~Triethylphenyl)acetophenone in

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Benzene
Photoproduct A(product) A(std.) Concentration <1)
Indanols 7.26507 23.16086 0.00149 0.47
Indanols 7.45212 23.74302 0.00149 0.47
Indanols 7.22500 22.81 123 0.00151 0.48
Indanols 7.20434 22.42082 0.00153 0.48
Indanols 7.51868 22.80132 0.00157 0.50
Indanols 7.09332 23.35354 0.00145 0.46
Indanols 7.38268 21.62746 0.00163 0.51
Indanols 7.26572 23.24797 0.00149 0.48

 

[Ketone]= 0.0307 M, [VP]= 0.1456 M, [C20]= 0.00328 M, 3.= 313 nm

Rf lndanols=1 .45, RfAP=2.90, Irradiation Time=2 hrs., Source= Mercury Arc Lamp

 

 

236

Quantum Yield Measurement for a-[Z-Bengylphenyl[acetophenone in Benzene
GC analysis: 1400 Varian GC
DB-225 Megabore column
Initial column temp.: 130°C
Initial col. hold time: 2 min.
Final col. temp.: 210°C

Rate: 20°C/min., Hold time: 5 min

Table 41. Product Quantum Yields of a-(2-Benzylphenyl)acetophenone in Benzene

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Photoproduct A(product) A(std.) Concentration <1)
Indanols 3.55851 18.36751 0.00057 0.41
Indanols 3.72227 19.22229 0.00057 0.41
Indanols 3.69135 19.28770 0.00056 0.41
Indanols 3.48125 19.31330 0.00053 0.38
Indanols 3.56177 18.25970 0.00057 0.41
Indanols 3.57529 19.49070 0.00054 0.39
Indanols 3.55951 19.35477 0.00054 0.39
Indanols 4.11391 22.20100 0.00055 0.40

 

[Ketone]= 0.0195 M, [VP]= 0.03 M, [C20]= 0.00328 M, 3.: 313 nm

Rf'"°‘"°ls=1 .34, Rf AP=2.90, Irradiation Time=2 hrs., Source= Mercury Arc Lamp

 

237

Quantum Yield Measurement for 01;] 2~Ethylphenyl[propiophenone in Benzene
GC analysis: 1400 Varian GC
DB-225 Megabore column
Initial column temp.: 100°C
Initial col. hold time: 5 min.
Final col. temp.: 195°C

Rate: 8 °C/min., Hold time: 5 min

Table 42. Product Quantum Yields of a-(2-Ethylphenyl)propiophenone in Benzene

 

 

 

 

 

 

 

 

 

 

 

 

 

Photoproduct A(product) A(std.) Concentration (D
Indanols 2.44339 1 1.27331 0.00029 0.061
Indanols 2.41312 10.37372 0.00031 0.066
Indanols 2.33439 9.97659 0.00032 0.066
Indanols 2.38892 9.97659 0.00033 0.068

2,3-Diarylbutanes 2.56981 1 1.27331 0.00029 0.061
2,3-Diarylbutanes 2.28177 10.37372 0.00028 0.059
2,3-Diarylbutanes 2.28231 9.97651 0.00030 0.62

Benzaldehydea 1.57951 4.53267 0.00190 0.43

Benzaldehydea 1.53167 4.44051 0.00188 0.42

Benzaldehydea 1.60169 4.41437 0.00198 0.44

 

 

 

 

a) Quantum yield determined in presence of thiol , l=313 nm

[Ketone]= 0.0216 M, [VP]= 0.118 M, [C17]= 0.0015 M, Source= Mercury Arc Lamp

Rf 1nd""°"=0.89, R,23'°‘""°““"“=0.85, R,B°""‘“""‘=4. 1, R,“"=3.0, Irradiation Time=6 hrs.

 

238

Quantum Yield Measurement for aj2,4,6-Triethylphenyl[propiophenone in
Benzene
GC analysis: 1400 Varian GC
DB~225 Megabore column
Initial column temp.: 100°C
Initial col. hold time: 5 min.

Final col. temp.: 195°C

Rate: 8 °C/min., Hold time: 5 min

Table 43. Product Quantum Yields of a~(2,4,6-Triethylphenyl)propiophenone in
Benzene

 

 

 

 

 

 

 

 

 

 

 

 

 

Photoproduct A(product) A(std.) Concentration <1)
Z,E~Indanol 1.62441 17.58086 0.00025 0.16319
Z,E-Indanol 1 .60987 18.18207 0.00024 0.15605
Z,E~Indanol 1.56916 17.44271 0.00024 0.15865
Z,E-Indanol 1.54773 17.98575 0.00023 0.15215
Z,E-Indanol I .52696 18.03058 0.00023 0.15215
E,Z-Indanol 1 .3 7224 18.14674 0.00021 0.13329
E,Z-Indanol 1.31834 18.03058 0.00020 0.12874
E,Z~Indanol 1.26739 17.83340 0.00019 0.12549
E,Z-Indanol 1 .40440 17.44271 0.00022 0.14174
E,Z-Indanol 1.46234 17.5886 0.00023 0.14629

 

 

 

 

 

[Ketone]= 0.0202 M, [VP]= 0.118 M, [C20]= 0.0033 M, Source= Mercury Arc Lamp

R,‘"““°"=1 .24, R,“"=3.0, Irradiation Time=6 hrs., x= 313 nm

 

239

MW
GC analysis: 1400 Varian GC
DB-225 Megabore column
Initial column temp.: 105°C
Initial col. hold time: 5 min.
Final col. temp.: 185°C

Rate: 6 °C/min., Hold time: 1 min.

Table 44. Product Quantum Yields of a-(Z-Ethylphenyl)acetone in Benzene

 

 

 

 

 

 

 

 

 

 

 

 

 

Photoproduct A(product) A(std.) Concentration <1)
Indanols 3.46544 45.64795 0.00048 0.01268
Indanols 3.43325 45.21899 0.00048 0.01268
Indanols 3.46251 43 .69783 0.00050 0.01285
Indanols 3.33783 44.1 1 101 0.00048 0.01228
Indanols 3.26094 43.41493 0.00047 0.01285

Diarylethane 6.69141 45.64795 0.00057 0.01495
Diarylethane 6.25961 45.21899 0.00053 0.01405
Diarylethane 7.01283 43.69783 0.00062 0.01601
Diarylethane 7.09688 44.1 1101 0.00062 0.01596
Diarylethane 6.62436 43.41493 0.00059 0.01504

 

 

 

 

 

[Ketone]= 0.0196 M, [VP]= 0.052 M, [C20]= 0.00351 M

Rf llnd““°"=1.8, Rf 2“W'~""""'~'-°‘=1.1, R, AP=2.9, Irradiation Time=20 hrs, 1:313 nm,

Source= Mercury Arc Lamp

 

Quantum Yield Measurement for a—Mesigylacetone in Benzene

240

CC analysis: 1400 Varian GC

DB~225 Megabore column

Initial column temp.: 100°C

Initial col. hold time: 1 min.

Final col. temp.: 195°C

Rate: 8 °C/min., Hold time: 10 min.

Table 45. Product Quantum Yields of a-Mesitylacetone in Benzene

 

 

 

 

 

 

 

 

 

 

 

 

Photoproduct A(product) A(std.) Concentration <1)
Indanol 15.16800 22.35858 0.00238 0.08686
Indanol - 15.51011 22.34461 0.00243 0.08868
Indanol 15.74424 22.88781 0.00241 0.08795
Indanol 15.97379 22.52081 0.0249 0.09087

Dimesitylethane 9.48040 22.35858 0.00149 0.05438
Dimesitylethane 9.69382 22.34461 0.00152 0.05547
Dimesitylethane 9.84015 22.8878] 0.00150 0.05474
Dimesitylethane 9.98362 22.52081 0.00155 0.05657
Dimesitylethane 9.83397 22.381 18 0.00154 0.05620
Dimesitylethane 9.80945 22.37678 0.001 54 0.05620

 

 

 

 

 

[Ketone]= 0.049 M, [VP]= 0.052 M, [C20]= 0.00351 M, Source= Mercury Arc Lamp

R,‘"“‘“°'S=1 .7, Rf2'3'9‘“'°"“"°5=1 .o, R,“’=2.9, Irradiation Time=20 hrs, 2:313 nm

 

 

241

Quantum Yield Measurement for aj2,4,6~Triethylphenyl[acetone in Benzene

NMR analysis: Gemini 300 MHz

Table 46. Product Quantum Yields of a-(2,4,6~Triethylphenyl)acetone in Benzene

 

 

 

 

 

 

 

 

 

 

Photoproduct A(product) A(std.) Concentration <1)
Indanol 4.9 62.4 0.0039 0.039
Indanol 4.3 64.5 0.0033 0.033
Indanol 5.2 64.5 0.0040 0.040

Diarylethane 2.3 62.4 0.0018 0.018
Diarylethane 2.3 64.5 0.0018 0.0018
Diarylethane 2.6 64.5 0.002 0.02

 

 

 

 

[Ketone]= 0.032 M, [VP]= 0.156 M, [Methyl benzoate]= 0.05 M
Irradiation Time=20 hrs, 1:313 nm

Irradiation Source= Mercury Arc Lamp

 

[H

 

 

242

Quantum Yield Measurement for 01;]2,4,6-Triisopropylphenyl[acetophenone in

Benzene

 

GC analysis: 3400 Varian GC
DB-l Megabore column
Initial column temp.: 65°C
Initial col. hold time: 5 min.
Final col. temp.: 225°C

Rate: 10 °C/rnin., Hold time: 22 min.

Table 47. Product Quantum Yields of a-(2,4,6~Triisopropylphenyl)acetophenone in
Benzene

 

 

 

 

 

 

 

 

 

2. (nm) %Conversion [Enol] chm. ' [Indanol] <1>.,,,,,,. ""

313 6 0.0065 0.35 - -

313 15 0.013 0.234 0.003 0.062
313 19 0.014 0.15 0.006 0.059
313 24 0.014 0.09 0.009 0.052
366 10 0.13 0.64 ' - -

366 18 0.18 0.64 0.024 0.085
366 25 0.24 0.64 0.034 0.085

 

 

 

 

 

 

a) Quantum yields were measured by NMR (b) Quantum yields were measured by GC
[Ketone]= 0.0143 M (GC studies), [Ketone]= 0.0983 M (NMR studies)

[VP]= 0.024 M (GC studies), [VP]= 0.1165 M (NMR studies)

[C20]= 0.0033 M (GC studies), [Methyl benzoate]= 0.03 M (NMR studies)

Rfl"°'“°'=1 .12, RfAP =1 .34, Irradiation Time=4 hrs, Irradiation Source= Mercury Arc

 

 

 

 

243

Quantum Yield Measurement for ajZ-Bengylphenyl[propiophenone in Benzene

NMR analysis: Gemini 300 MHz

Table 48. Product Quantum Yields of a-(Z-Benzylphenyl)propiophenone in Benzene

 

 

 

 

 

 

 

 

Photoproduct A(product) A(std.) Concentration (D
Z,Z~Indanol 0.57 1 1.05 0.0033 0.052
Z,Z~Indanol 0.51 9.36 0.0034 0.053
Z,Z~Indanol 0.54 9.34 0.0036 0.056
Z,E-Indanol 0.54 1 1.05 0.0031 0.049
Z,E-Indanol 0.42 9.36 0.0029 0.045
Z,E-Indanol 0.42 9.34 0.0029 0.045

 

 

 

 

 

 

[Ketone]= 0.0113 M, [VP]= 0.166 M, [Methyl benzoate]= 0.064 M
Irradiation Time=8 hrs, l=313 nm

Irradiation Source= Mercury Arc Lamp

 

244

Quantum Yield Measurement for 01:] 2,4,6-Triisopropylphenyl[acetone in Benzene
GC analysis: 1400 Varian GC
DB~225 Megabore column
Initial column temp.: 100°C
Initial col. hold time: 5 min.
Final col. temp.: 185°C

Rate: 8 oC/min., Hold time: 5 min.

Table 49. Product Quantum Yields of a—(2,4,6~Triisopropylphenyl)acetone in
Benzene

 

 

 

 

 

 

 

 

 

 

 

Photoproduct A(product) A(std.) Concentration CD
Indanol 2.69067 66.80157 0.0002 0.009
Indanol 2.64648 66.75248 0.0002 0.009
Indanol 2.68319 66.19910 0.0002 0.009

Diarylethane 2.03309 66.80157 0.00009 0.004
Diarylethane 1.85067 66.75248 0.00008 0.004
Diarylethane 2.06752 66.19910 0.00009 0.004.
Enol 0.15 22.5 0.0036 0.028
Enol 0.18 231 0.0042 0.032
Enol 0.15 22.3 0.0036 0.028

 

 

 

 

 

 

[Ketone] = 0.0245 m, [VP]= 0.03 M, [C20]= 0.0035 M
R,"‘“‘“°"=1 .0, sz'3'D‘W'°"""°‘=0.62, R,“’=2.9, Irradiation Time=20 hrs, 2:313 nm

Irradiation Source= Mercury Arc Lamp

245

Quantum Yield Measurements for 2j2’j2’éhDimethyllbutyl[benzophenone

NMR analysis: Gemini 300 MHz

Table 50. Product Quantum Yields of 2-(2’~(2’,3’~Dimethyl)butyl))benzophenone

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Solvent Photoproduct A(product) A(std.) Concentration (D

Benzene 151ndmZ 0.98 17.84 0.0021 0.026
Benzene 15indmZ 1.19 18.54 0.0024 0.028
Benzene 15inde 2.17 17.84 0.0046 0.052
Benzene 15inde 2.20 18.54 0.0045 0.052
Benzene 15indip 0.47 17.84 0.0010 0.01

Benzene 15indip 0.35 18.54 0.0008 0.009
Benzene 15alc 0.28 17.84 0.0006 0.006
Benzene 15alc 0.24 18.54 0.0005 0.005
Methanol 151ndmZ 3.26 12.3 0.0037 0.116
Methanol lSinde 3 .72 12.3 0.0042 0.132
Methanol 15indip 2.98 12.3 0.0034 0.107
Methanol 15alc 1.65 12.3 0.0019 0.06

 

 

 

 

 

 

[Ketone]= 0.0145 M, [VP]= 0.131 M, [MB]= 0.04 M

Irradiation Time=8 hrs, 7t=313 nm, Irradiation Source= Mercury Arc Lamp

 

 

246

Table 51. Quenching of the Indanol Formation in a-(Z-Ethylphenyl)acetophenone
with 2,5-Dimethyl-2,4~hexadiene at 313 nm in Benzene

 

 

 

 

 

 

 

[Q] A(product)/A(std.) <1>°/<I>
0.00 0.145 1.00
0.0046 0.138 1.05
0.0092 0.135 1.07
0.0138 0.131 1.11
0.0184 0.127 1.14

 

 

 

 

[Ketone] = 0.032 M

Table 52. Quenching of the Indanol Formation in a-(2,4,6-Triethylphenyl)
acetophenone with 2,5-Dimethyl-2,4~hexadiene at 313 nm in Benzene

 

 

 

 

 

 

[Q] A(product)/A(std.) <l>°/<D
0.00 0.094 1 .00
0.0046 0.089 1.06
0.0092 0.088 1.07
0.0138 0.084 1.12

 

 

 

 

[Ketone] = 0.075 M

 

247

Table 53. Quenching of the Indanol Formation in a—(Z-Benzylphenyl)acetophenone
with 2,5~Dimethyl~2,4~hexadiene at 313 nm in Benzene

 

 

 

 

 

 

 

1Q] A(product)/A(std.) <D°/<D
0.00 0.393 1 .00
0.00978 0.378 1.04
0.0195 0.356 1.07
0.0293 0.348 1.10
0.0391 0.327 1 . 16

 

 

 

[Ketone] = 0.085 M

kqt=4

Table 54. Quenching of the Indanol Formation in a-(2-Ethylphenyl)propiophenone
with 2,5-Dimethyl-2,4~hexadiene at 313 nm in Benzene

 

 

 

 

 

 

 

[Q] A(product)/A(std.) <b°/<I>
0.00 0.056 1.00
0.00978 0.0422 1.32
0.0195 0.0393 1.42
0.0293 0.035 1.60
0.0391 0.034 1.7

 

 

 

[Ketone] = 0.064 M

kq‘t = 17.4

 

 

 

248

Table 55. Quenching of the Indanol Formation in a-(2,4,6-Triethylphenyl)
propiophenone with 2,5-Dimethyl-2,4~hexadiene at 313 nm in Benzene

 

 

 

 

 

 

 

[Q] A(product)/A(std.) <D°/<D
0.00 0.4241 1.00
0.00978 0.3876 1.06
0.0195 0.352 1.17
0.0293 0.3278 1.26
0.0391 0.3198 1.29

 

 

 

[Ketone] = 0.0825 M

Table 56. Quenching of the Indanol Formation in 2'-(2,3~Dimethyl~2~
butyl)benzophenone with 2,5-Dimethyl-2,4~hexadiene at 313 nm in Benzene

 

 

 

 

 

 

[Q1 A(product)/A(std.) d>°/<b
0.00 0.0595 1.00
0.025 0.0365 1.63
0.062 0.025 2.38
0.079 0.0225 2.64

 

 

 

[Ketone] = 0.0051 M

qu = 20.8

 

 

 

249

Table 57. Quenching of the Diarylethane Formation in a—(2-Ethylphenyl)acetone
with 2,5-Dimethyl-2,4~hexadiene at 313 nm in Benzene

 

 

 

 

 

 

[Q] A(product)/A(std.) <1>°/<1>
0.00 0.333 1 .00
0.0046 0.318 1.05
0.0092 0.315 1.06
0.0138 0.302 1.10

 

 

 

 

[Ketone] = 0.0075 M

kqt = 6.7

Table 58. Quenching of the Diarylethane Formation in a-Mesitylacetone with 2,5-
Dimethyl~2,4-hexadiene at 313 nm in Benzene

 

 

 

 

 

 

[Q] A(product)/A(std.) <D°/(l>
0.00 0.586 1 .00
0.0046 0.517 1.133
0.0092 0.4795 1 .222
0.0138 0.4035 1.452

 

 

 

 

[Ketone] = 0.0312 M

kqt=31.4

 

250

Table 59. Quenching of the Diarylethane Formation in a-(2,4,6~Trisiopropylphenyl)
acetone with 2,5-Dimethyl-2,4~hexadiene at 313 nm in Benzene

 

 

 

 

 

 

[Q] A(product)/A(std.) (D°/(D
0.00 0.1 36 1 .00
0.0092 0.067 - 2.03
0.0138 0.054 2.52
0.0184 0.046 2.96

 

 

 

 

[Ketone] = 0.006 M

kqt=107.1

 

251

References:

1. Jablonski, A. Z. Physik. 1935, 94, 38.
2. Cowen, D. O.; Drisco, R. L. “Elements of Organic Photochemistry”, Academic Press,
New York, N.Y., 1969.
3. Turro, N. J. in “Modern Molecular Photochemistry”, Benjamin-Cummings, Menlo
Park, Ca, 1978.
4. Halpren, A.; Ware, W. R. J. Chem. Phys. 1970, 53, 1969.
5. Almgren, M Mol. Photochem. 1972, 4, 327.
6. a) Morris, J. M.; Williams, D. F. Chem. Phys. Lett. 1974, 25, 312.

b) E1~Sayed, M. A.; Leyerle, R. J. Chem. Phys. 1975, 62, 1579.

c) Bately, M.; Kearns, D. R. Chem. Phys. Lett. 1968, 2, 423.
7. a) Matsumoto, T.; Sato, M.; Hiroyama, S. Chem. Phys. Lett. 1972, I3, 13.

b) Hansen, D. A.; Lee, K. C. J. Chem. Phys. 1975, 62, 183.

c) Anderson, R. W.; Hochstrasser, R. M.; Lutz, H.; Scott, G. W. J. Chem. Phys. 1974,
61, 2500.
8. a. Wagner, P. J .; Kochevar, I. J. Am. Chem. Soc. 1968, 90, 2232.

b. Clark, W. D.; Litt, A. D.; Steel, C. J. Am. Chem. Soc.1969, 91, 5413.

c. Herkstroeter, W. G.; Jones, L. B.; Hammond, G. S. J. Am. Chem. Soc. 1966, 88,
4777.
9. Turro, N. J. “Modern Molecular Photochemistry”, Benjamin-Cummings, Menlo Park,
Ca. 1978.
10. Wagner, P. J. in “Rearrangements in Ground and Excited Molecules”, Academic
Press, New York, N. Y. 1980, V3, 381.
11. Wagner, P. J. Topic in Curr. Chem. 1976, 66, 1.
12. a) Yang, N. C.; McClure, D. S.; Murov, S. L.; Houser, J. J.; Dusenberry, R. J. Am.
Chem. Soc. 1967, 89, 5466.

b) Yang, N. C.; Dusenberry, R. L. J. Am. Chem. Soc. 1968, 90, 5899.
13. Wagner, P. J. ; Kemppainen, A. E.; Schott, H. N. J. Am. Chem. Soc. 1973, 95, 5604.
14. Wagner, P. J.; Thomas, M. J.; Harris, E. J. Am. Chem. Soc. 1976, 98, 7675.
15. Scaiano, J. C.; Leigh, W. J.; Meador, M. A.; Wagner, P. J. J. Am. Chem. Soc. 1985,
107, 5806.
16. a) Norrish, R. G. W.; Bamford, C. H. Nature 1936, 138, 1016.

b) Norrish, R. G. W.; Bamford, C. H. Nature 1937, 140, 195.

17. a) Heine, H. G.; Hartmann, W.; Kory, D. R.; Magyar, J. G.; Hoyle, C. E.; McVey, J.
K.; Lewis, F. D. J. Org. Chem. 1974, 39, 691.

b) Lewis, F. D.; Hoyle, C. H.; Magyar, J. G. J. Org. Chem. 1975, 40, 488.

c) Lewis, F. D.; Magyar, J. G. J. Am. Chem. Soc. 1973, 95, 5973.
18. Zimmerman, H. E. Adv. Photochem. 1963, 1, 183.
19. Gray, P.; Williams, A. Chem. Rev. 1959, 59, 239.
20. Walling, C.; Padwa, A. J. Am. Chem. Soc. 1963, 85, 1593.
21. Lewis, P. D.; Magyar, J. G. J. Org. Chem. 1972, 37, 2102.
‘ 22. Baum, A. A. J. Am. Chem. Soc. 1972, 94, 6866.

 

252

23. Hamer, N. K. J. Chem. Soc: Perkin 1 1979, 1285.
24. Padwa, A.; Au, A. J. Am. Chem. Soc. 1976, 98, 5581.
25. a) Dalton, J. C.; Dawes, K.; Tmro, N. J.; Weiss, D. S.; Baltrop, J. A.; Coyle, J. D. J.
Am. Chem. Soc. 1971, 93, 7213.
b) Dalton, J. C.; Pond, D. M.; Weiss, D. S.; Lewis, F. D.; Turro, N. J. J. Am. Chem.
Soc. 1970, 92, 2564.
26. Yang, N. C.; Feit, E. D.; Hui, M. H.; Turro, N. J.; Dalton, J. C. J. Am. Chem. Soc.
1970, 92, 6974.
27. Heine, H. G. Justus Liebigs Ann. Chem. 1970, 105, 732.
28. Wagner, P. J. Acc. Chem. Res. 1971, 4, 168.
29. Wagner, P. J.; Park, B. S. Org Photochem. 1991, 11, 227.
30. Gilbert, A.; Baggott, J. in “Essentials of Molecular Photochemistry”; CRC Press:
Boca Raton, F1, 1991; pp 287-352.
31. a) Walling, C.; Gibian, M. J. Am. Chem. Soc. 1965, 87, 3361.
b) Padawa, A. Tetrahedron Lett. 1964, 3465.
32. Walling, C.; Padwa, A. J. Am. Chem. Soc. 1964, 85, 1593.
33. Wagner, P. J. J. Am. Chem. Soc. 1967, 89, 5898.
34. Wagner, P. J. Acc. Chem. Res. 1983, 16, 461.
35. Wagner, P. J .; Chen, C. P. J. Am. Chem. Soc. 1976, 98, 239.
36. a) Wagner, P. J.; Meador, M. A. J. Am. Chem. Soc. 1983, 105, 4484.
b) Wagner, P. J.; Meador, M. A. J. Am. Chem. Soc. 1984, 106, 3684.
c) Wagner, P. J.; Scaiano, J. C. J. Am. Chem. Soc. 1984, 106, 4626.
d) Wagner, P. J.; Zhou, B. J. Am. Chem. Soc. 1988, 110, 611.
e) Wagner, P. J .; Zhou, B. Tetrahedron Lett. 1989, 30, 53 89.
f) Wagner, P. J .; Zhou, B. Tetrahedron Lett. 1990, 31, 2251.
g) Wagner, P. J .; Hasegawa, T.; Zhou, B. J. Am. Chem. Soc. 1991, 113. 9640.
37. Lewis, F. D.; Johnson, R. W.; Johnson, D. E. J. Am. Chem. Soc. 1974, 96, 6090.
38. a) Haag, R.; Wirz, J.; Wagner, P. J. Hel. Chim. Acta. 1977, 60, 2595.
b) Sammes, P. G. Tetrahedron 1976, 32, 405.
39. Turro, N. J.; Weiss, D. W. J. Am. Chem. Soc. 1968, 90, 2185.
40. Scheffer, J. R.; Trotter, J.; Omkaram, N.; Evans, S.; Ariel, S. Mol. Cryst. Liq. Cryst.
1986, 134, 169.
41. Scheffer, J. R.; Dzakpasu, A. A. J. Am. Chem. Soc. 1978, 100, 2163.
.42. Severance, D.; Pandey, B.; Morrison, H. J. Am. Chem. Soc. 1987, 109, 3231.
43. Sugiyama, N.; Nishio, T.; Yamada, K.; Aoyarna, H. Bull. Chem. Soc. Japan 1970, 43,
1879. '
44. Lahav, M.; Chang, H. C.; Popovitz-Biro, R.; Leiserowitz, L. J. Am. Chem. Soc. 1987,
109, 3883.
45. Matsuura, T.; Ito, Y. Tetrahedron Lett. 1988, 29, 3087.
46. Sauers, R. R.; Scimone, A.; Shams, H. J. Org. Chem. 1988, 53, 6084.
47. Sauers, R. R.; Scaiano, J. C.; Bliss, R. A.; McGimpsey, W. G.; Casal, H. L. J. Am.
Chem. Soc. 1986, 108, 8225.
48. Wagner, P. J.; Kelso, P.; Kemppainen, A. K.; Zepp, R. J. Am. Chem. Soc. 1972, 94,
7500.

253

49. Scheffer, J. R.; Ariel, S.; Ramamurthy, V.; Trotter, J. J. Am. Chem. Soc. 1983, 105,
6959.
50. a) Houk, K. N.; Dorigo, A. E. J. Am. Chem. Soc. 1987, 109, 2195.
b) Houk, K. N. ; Dorigo, A. E.; Tucker, J. Acc. Chem. Res. 1990, 23, 107.
51. Houk, K. N.; Dorigo, A. E.; McCarrick, M. A.; Loncharich, R. J. J. Am. Chem. Soc.
1990, 112, 7508.
52. Sauers, R. R.; Krogh-Jesperson, K. Tetrahedron Lett. 1989, 30, 527.
53. Sauers, R. R.; Huang, 8. U. Tetrahedron Lett. 1990, 31 , 5709.
54. Wagner, P. J.; Giri, B. P.; Pabon, R.; Singh, S. B. J. Am. Chem. Soc. 1987, 109, 8104.
55. Wagner, P. J.; Meador, M. A.; Giri, B. P.; Scaiano, J. C. J. Am. Chem. Soc. 1985, 107,
1087. ,
56. Wagner, P. J.; Giri, B. P.; Scaiano, J. C.; Ward, D. L.; Gabe, E.; Lee, F. L. J. Am.
Chem. Soc. 1985, 107, 5483.
57. Wagner, P. J.; Pabon, R.; Park, B. S.; Zand, A. R. Ward, D. L. J. Am. Chem. Soc.
1994, 116, 589.
58. Wagner, P. J.; Hasegawa, T.; Zhou, B. J. Am. Chem. Soc. 1991, 113, 9640.
59. a) Wagner, P. J .; Hammond, G. S. J. Am. Chem. Soc. 1965, 87, 4009.
b) Dougherty, T. J. J. Am. Chem. Soc. 1965, 87, 4011.
c) Coulson, D. R.; Yang, N. C. J. Am. Chem. Soc. 1966, 88, 4511.
d) Yang, N. 0; Elliott, S. P.; Kim, B. J. Am. Chem. Soc. 1969, 91 , 7551.
60. Dalton, J. C.; Turro, N. J. Annu. Rev. Phys. Chem. 1970, 21, 499.
61. Yang, N. C.; Elliott, S. P. J. Am. Chem. Soc. 1969, 91, 7550.
62. Stephenson, L. M.; Cavigli, P. R.; Parlett, J. L. J. Am. Chem. Soc. 1971, 93, 1984
63. Heller, A. Mol. Photochem. 1969, I, 257.
64. Hammond, G. S. Advan. Photochem. 1969, 7, 373.
65. Salem, L. J. Am. Chem. Soc. 1974, 96, 3482.
66. Scaiano, J. C.; Nau, W. M.; Cozens, F. L. J. Am. Chem. Soc. 1996, 118, 2275.
67. Noh, T.; Lei, X.~G.; Turro, N. J. J. Am. Chem. Soc. 1993, 115, 3105.
68. Turro, N. J .; Wan, P. Tetrahedron Lett. 1984, 25, 3655.
69. De Mayo, P.; Nakamura, N., Tsang, P. W. K.; Wong, S. K. J. Am. Chem. Soc. 1982,
104, 6824.
70. Wagner, P. J.; Park, B. ~S.; Sobczak, M.; Frey, J.; Rappoport, Z. J. Am. Chem. Soc.
1995, 11 7, 7619. '
71. Evans, S. E.; Omkaram, N.; Scheffer, J. R.; Garcia-Garibay, M.; Trotter, J. J. Am.
Chem. Soc. 1986, 108, 5648.
72. Evans, S. E.; Omkaram, N.; Scheffer, J. R.; Trotter, J. Tetrahedron Lett. 1985, 26,
5903.
73. Evans, S. E.; Omkaram, N.; Scheffer, J. R.; Trotter, J. Tetrahedron Lett. 1986, 27,
1419.
74. Scaiano, J. C. Tetrahedron 1982, 38, 819.
75. Salem, L.; Rowland, C. Angew. Chem. , Int. Ed. Engl. 1972, 11, 92.
76. Michl, J. J. Am. Chem. Soc. 1996, 118, 3568.
77. Wagner, P. J .; Kochevar, I. E.; Kemppainen, A. E. J. Am. Chem. Soc. 1972, 94, 7489.
78. Small Jr., R. D.; Scaiano, J. C. Chem. Phys. Lett. 1978, 59, 246.
79. Small Jr., R. D.; Scaiano, J. C. J. Phys. Chem. 1977, 81, 828, 2126.

254

80. Wagner, P. J. Acc. Chem. Res. 1989, 22, 83.
81. Turro, N. J .; Buchachenko, A. L.; Tarasov, V. F. Acc. Chem. Res. 1995, 28, 69.
82. Closs, G, Forbes, M. D. E.; Piotrowiak, P.. J. Am. Chem. Soc. 1992, 114, 3285.
83. Griesbeck, A. G.; Stadtmuller, S. J. Am. Chem. Soc. 1991, 113, 6923.
84. Griesbeck, A. G.; Stadtmuller, S. J. Am. Chem. Soc. 1990, 112, 1281.
85. Hart, H.; Giguere, R. J. J. Am. Chem. Soc. 1983, 105, 7775.
86. Hart, H.; Lin, L. T. W. Tetrahedron Lett. 1985, 26, 575.
87. Wagner, P. J.; Meador, M. A.; Zhou, B.; Park, B. ~S. J. Am. Chem. Soc. 1991, 113,
9630.
88. Park, B. S. Ph. D. Dissertation, 1992, Michigan State University, 157-199.
89. Pappas, S. P.; Blackwell, J. E. Tetrahedron Lett. 1966, 1175.
90. Pappas, S. P.; Zehr, R. D.; Blackwell, J. E. J. Heterocycl. Chem. 1970, 1215.
91. Wagner, P.J.; Meador, M. A.; Park, B. S. J. Am. Chem. Soc. 1990, 112, 5199.
92. a) Marshall; Prager Aust. J. Chem. 1979, 32, 1261.
b) Scholl, B.; Jolidon, S.; Hansen, H.~J. Helv. Chim. Acta 1986, 69, 184.
c) Morrison, H.; Giacherio, D. J. Org. Chem. 1982, 47, 1058.
93. Montgomery, M. E.; Wirth, M. J. Anal. Chem. 1992, 64, 2566.
94. Zielinski, W.; Mazik, M. Pol. J. Chem. 1992, 66, 661.
95. Scheffer, J. R. in “Organic Solid State Chemistry”; Desiraju, G. R. Ed.; Elsevier, New
York, 1987; Chapter 1.
96. a) Closs, G. L. Adv. Magn. Res. 1975, 7, 1.
b) Closs, G. L.; Doubleday, C. J. Am. Chem. Soc. 1973, 95, 2735.
c) Kaptein, R.; Dekanter, F. J. Am. Chem. Soc. 1982, 104, 4759.
d) Carlacci, L.; Doubleday, C.; Furlani, T.; King, H.; Mciver, J.; J. Am. Chem. Soc.
1987,109, 5323.
e) Carrington, A.; McLauchlan, A. Introduction to Magnetic Resonance, Harper and
Row; New York, 1967.
97. Doubleday, C. Jr.; Turro, N. J.; Wang, J~F. Acc. Chem. Res. 1989, 22, 199.
98. Zimmt, M. B.; Doubleday, C. Jr.; Gould, I. R.; Turro, N. J. J. Am. Chem. Soc. 1985,
107, 6724.
99. Zimmt, M. B.; Doubleday, C. Jr.; Turro, N. J. J. Am. Chem. Soc. 1986, 108, 3618.
100. Biali, S. E.; Rappoport, Z. J. Am. Chem. Soc. 1984, 196, 5641.
101. Old, M.; Iwamura, H.Tetrahedron 1968, 24, 1905.
102. Zhou, B. Ph. D. Dissertation, 1988, Michigan State University.
103. Wagner, P. J.; Meador, M. A.; Scaiano, J. C. J. Am. Chem. Soc. 1984, 106, 7988.
104. Wagner, P. J .; J. Am. Chem. Soc. 1967, 89, 2820.
105. Scheffer, J. R. Org. Photochem 1987, 8, 249.
106. Burke, S. D.; Silks, L. A.; Strickland, S. M. S. Tetrahedron Lett. 1988, 29, 2761.
107. Chandler, W. D.; Goodman, L. J. Mol. Spectrosc. 1970, 35, 232.
108. Lewis, F. D.; Johnson, R. W.; Johnson, D. E. J. Am. Chem. Soc. 1974, 96, 6090.
109. Wagner, P. J.; Kochevar, I. E.; Kemppainen, A. E. J. Am. Chem. Soc. 1972, 94,
7489.
110. Encinas, M. V.; Lissi, E. A.; Lemp, E.; Zanocco, A.; Scaiano, J. C. J. Am. Chem.
. Soc. 1983, 105, 1856.

 

255

111. a) Ariel, S.; Evans, S. V.; Garcia-Garibay, M.; Harkness, B. R.; Omkaram, N.:
Scheffer, J. R.; Trotter, J. J Am. Chem. Soc. 1989, 111, 5591.

b) Lewis, T. J .; Rettig, S. J .; Scheffer, J. R.; Trotter, J .: Wierko, F.; J. Am. Chem. Soc.
1990, 112, 3679.

112. a) Dewar, M. J. S.; Zoebisch, E. G.; Healy, H. F.; Stewart, J. J. P. J. Am. Chem. Soc.
1985, 107, 3902.

b) Stewart, J. J. P. J. Comp. Chem. 1989, 10, 209, and references therein.

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