PART I:

PART II:

0—7639

LIBRARY

Michigan State
Unrvasby‘

 

This is to certify that the

thesis entitled

INTRAMOLECULAR CHARGE-TRANSFER QUENCHING
OF EXCITED STATES BY SULFUR

RADICAL B-CLEAVAGE VIA EXCITED STATESAND
PHOTOGENERATED DIRADICALS
presented by

Michael Jeffrey Lindstrom ;

has been accepted towards fulfillment
of the requirements for

Chemistry

4!”

/£jor profeésor

Ph. D. degree in

 

 

PART I

INTRAMOLECULAR CHARGE-TRANSFER QUENCHING
OF EXCITED STATES BY SULFUR

PART II

RADICAL B-CLEAVAGE VIA EXCITED STATES
AND PHOTOGENERATED DIRADICALS

BY

Michael Jeffrey Lindstrom

A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Chemistry

1978

ABSTRACT

PART I

INTRAMOLECULAR CHARGE-TRANSFER QUENCHING
OF EXCITED STATES BY SULFUR

PART II

RADICAL B-CLEAVAGE VIA EXCITED STATES
AND PHOTOGENERATED DIRADICALS

BY
Michael Jeffrey Lindstrom

PART I

The photochemistry of various benzoylsulfides,
sulfoxides, and sulfones was studied to determinelfluaeffect
of chain length upon the rate of interaction of the
excited benzoyl with the sulfur moiety.

In general, the rate of charge-transfer quenching
increases as the number of carbons between the donor and
acceptor decreases, with the exception of the a-thioalkoxy-
acetophenones, which quench more slowly than the B- and
y-thioalkoxyketones. The observed trend is rationalized
in terms of the ease of formation of various sized rings,
which,jJ1turn, corresponds to approach of donor and accep-
tor. Increasing the oxidation state of the sulfur group
also dramatically decreases the rate of charge-transfer
quenching;

In addition to Type II fragmentation, the a-thio-

alkoxyacetophenones undergo competitive B-cleavage ix:

Michael Jeffrey Lindstrom

varying degrees. The extent of B-cleavage is found to
depend upon the nature of the leaving group. For instance,
2-methylsulfinylacetophenone reacts exclusively via
B-cleavage, whereas for 2-thiomethylacetophenone such cleav-
age is a minor pathway. The competition between y-hydrogen
abstraction and B-cleavage was separated and its effect
upon kct determined.

The rate data obtained through the standard Stern-
Volmer analysis were separated into inductive and resonance
constituents. The following order, listed in decreasing
ability to stabilize an adjacent radical center, was deter-
mined: OMe > SPh ~ SBu ~ OPh > OH > 80311 > Ph > Me > SOZMe.

PART II

Phenacylsulfides

 

A number of substituted phenacylsulfides were synthe-
sized and studied to further investigate the nature of
B-cleavage.

All compounds studied underwent photoinduced
B—cleavage in benzene with the concomitant production of
the appropriate acetophenones and radical coupling products.
The addition of 0.05M benzenethiol was observed to maximize
the quantum yields and eliminate the formation of out-of-
cage coupling products.

The rate constants of B-cleavage were determined by
standard Stern-Volmer analysis. Electron donating substitu-

ents on the benzene ring decrease the rate of B-cleavage

Michael Jeffrey Lindstrom

significantly. The rate of B-cleavage is also dependent on
the nature of the leaving group. Relative rates of
B-cleavage for various groups were determined as follows:

SPh > SOMe > StBu > SOzMe.

6-Substituted Phenyl Ketones

 

A variety of 5-substituted phenyl ketones were syn-
thesized and studied. All compounds formed varying amounts
of 4-benzoyl-l-butene in addition to acetophenone upon uv
irradiation. The effect of solvent upon the ratio of
Type II products to 4-benzoyl-l-butene is negligible,
indicating that elimination of HX was occurring by a free
radical pathway rather than ionically. The mechanism was
determined to proceed by initial 1,4 diradical formation
followed by B-cleavage and rapid in-cage disproportionation
to yield 4-benzoyl-l-butene and HX. Comparison of Type II
products to 4-benzoyl-l-butene ratios allowed calculation
of relative rates of B-cleavage for a variety of groups.

A novel cyclic phenyl ketone system in which the
6-substituents and benzoyl groups are inaccessible to each
other was synthesized. Smooth photolytic elimination of HX
in these cases was observed. Afairly large rate enhancement
for y-hydrogen abstraction was observed for trans-4-bromo-
l,4-dimethyl-l-benzoylcyclohexane and is attributed to
anchimeric assistance by bromine.

Competitive a-cleavage in these compounds revealed

information concerning ground state equilibria.

To Joan

p.
5.4.

ACKNOWLEDGMENTS

The author wishes to thank Professor Peter J. Wagner
for his inspiring guidance throughout the course of this
endeavor. His friendship, advice, and sense of humor have
made the years of "courses and requirements" at M.S.U. very
enjoyable. It has indeed been a privilege and a pleasure
to work with him.

The author would also like to thank the Chemistry
Department at M.S.U. for financial support and the use of
its excellent facilities. Thanks also to the NSF for
research assistantships administered by Dr. Wagner.

Very special thanks is extended to my parents,
grandparents, relatives, and friends for their support and
encouragement.

My wife, Joan, deserves the author's deepest appre-
ciation for her patience, companionship, and support. Her
editorial comments, advice, and typing of the manuscript

proved invaluable.

iii

TABLE OF CONTENTS

LIST OF TABLES . . . . . . . . . . .
LIST OF FIGURES . . . . . . . . . .
LIST OF SCHEMES . . . . . . . . . .
INTRODUCTION . . . . . . . . . . .
Objectives and Organization . . .
The Norrish Type II Reaction . .
Charge-Transfer . . . . . . . . .

Energy Transfer . . . . . . . . .

The Norrish Type I Reaction, a-Cleavage

B-Cleavage . . . . - . . . . . .

Stern-Volmer Kinetics . . . . . .

PART I. INTRAMOLECULAR CHARGE-TRANSFER QUENCHING

OF EXCITED STATES BY SULFUR . . .

Results . . . . . . . . . . . . .

Preparation and Product Identification . . .

Quantum Yields . . . . . . . .
Quenching Studies . . . . . .
Intersystem Crossing Yields .
Discussion . . . . . . . . . . .

General Observations . . . . .

Rate of Hydrogen Abstraction Versus Inductive

and Resonance Effects . . .

iv

Page
xi
xv

xvii

12
15

17
17
17
18
l9
19
30

3O

32

Page

Competitive B-Cleavage and Y-Hydrogen
Abstraction . . . . . . . . . . . . . . . . 38

Charge-Transfer Quenching . . . . . . . . . . . 4l
Conformational Effects . . . . . . . . . . . 42
Effect of Donor on kct . . . . . . . . . . . 45
Bimolecular Quenching . . . . . . . . . . . 48

Indications for Further Research . . . . . . . 49
Synthetic Utility . . . . . . . . . . . . . 49
Products from C-T State . . . . . . . . . . 50
Effect of Ring Substituents . . . . . . . . 50
Nature of Quenching by the Sulfonyl Group . . 50

Energy Transfer Resulting in Homolytic
Cleavage . . . . . . . . . . . . . . . . 51

PART II. RADICAL B-CLEAVAGE VIA EXCITED STATES
AND PHOTOGENERATED DIRADICALS . . . . . . . . . . 52

Phenacylsulfides (Results) . . . . . . . . . . . . 52
Synthesis and Identification of Photoproducts . . 52
Quantum Yields . . . . . . . . . . . . . . . . 53
Quenching Studies . . . . . . . . . . . . . . . 53
Intersystem Crossing Yields . . . . . . . . . . 54
Spectroscopic Studies . . . . . . . . . . . . . 54

Phenacylsulfides (Discussion) . . . . . . . . . . 68
Mechanism . . . . . . . . . . . . . . . . . . . 68
Quantum Yields . . . . . . . . . . . . . . . . 72
Spectroscopy . . . . . . . . . . . . . . . . . 74

Rates of B-Cleavage and Charge-Transfer . . . . 79

Indications for Further Research . . .
Estimation of In-Cage Coupling . .
Generation of Free Radicals . . . .

6-Substituted Phenyl Ketones (Results) .

Synthesis . . . . . . . . . . . . . .

Identification of Diastereomers . . .

Identification of Photoproducts . . .

Quantum Yields . . . . . . . . . . . .

Quenching Studies . . . . . . . . . .

6-Substituted Phenyl Ketones (Discussion)

Mechanism of Radical B-Cleavage via
Photogenerated Diradicals . . . . .

Quantum Yields and Other Observations
Rates of B-Elimination . . . . . . . .

y-Hydrogen Abstraction and Anchimeric
Assistance . . . . . . . . . . . .

Conformational Effects . . . . . . . .
Indications for Further Research . . .
Synthetic Utility . . . . . . . . .

Relative Rates of 8-Cleavage . . .
B-Substituted Butyrophenones . . .
Inductive Effects . . . . . . . . .
EXPERIMENTAL . . . . . . . . . . . . . . . .
Preparation and Purification of Materials
Solvents and Additives . . . . . . . .
Benzene . . . . . . . . . . . . . .

Methanol . . . . . . . . . . . . .

vi

Page
84
84
85
85
85
87
89
91
91

101

101
106
107

112
114
119
119
119
120
120
121
121
121
121

121

Dioxane . . . .
Pyridine . . . .
Acetonitrile .
Ethanol . . . .
Hexane . . . . .
Pentane . . . .
Benzenethiol . .
Internal Standards
Dodecane . . .
Tetradecane .
Hexadecane . .
Heptadecane .
Octadecane . . .
Nonadecane . . .
Quenchers . . . . .

Napthalene . . .

1-Methylnapthalene .

cis- and trans-1,3-Pentadiene

cis-1,3-Pentadiene

n-Butylsulfide .
.n-Butylsulfoxide
n-Butylsulfone .
Ketones . . . . . .
Acetophenone . .
Valerophenone

Butyrophenone .

vii

Page
121
121
121
122
122-
122
122
122
122
122
122
122
122
122
122
122
122
123
123
123
123
123
123
123
123
123

Phenacylchloride . . . . . . . . . .
Phenacylbromide . . . . . . . . . . .
B-Bromopropiophenone . . . . . . . .

y-Chlorobutyrophenone . . . . . . . .
6—Chlorovalerophenone . . . . . . .
s-Chlorohexanophenone . . . . . . . .
2-Thiomethylacetophenone . . . . . .
2-Thiobutylacetophenone . . . . . . .
2-Thio-t-butylacetophenone . . . . .
2-Thiophenylpropiophenone . . . . .
2-Thiophenylisobutyrophenone . . . .
Phenyldesylsulfide . . . . . . . . .
2-Thiophenylacetophenone . . . . . .
2-Thiophenyl-4'-f1uoroacetophenone .
2-Thiophenyl-4'-chloroacetophenone .
2-Thiophenyl-4'-bromoacetophenone . .
2-Thiophenyl-4'-methylacetophenone .
2-Thiophenyl-4'-methoxyacetophenone .
2-Thiopheny1-4'-thiomethylacetophenone
2-Thiophenyl-4'-cyanoacetophenone .

2-Thiophenyl-4'-pheny1acetophenone .

2-Thiophenyl—4'-dimethylaminoacetophenone

l-Benzoyl-l-thiophenylcyclopropane
4'-Thiophenylmethylacetophenone . . .
3-Thiobuty1propiophenone . . . . .

4-Thiobutylbutyrophenone . . . . . .

viii

Page
124
124
124
124
124
124
125
125
125
125
125
125
125
125
125
126
126
126
126
126
126
126
127
127
128

128

4-Thio-t-butylbutyrophenone .
4-Thiophenylbutyrophenone .

5-Thiobutylvalerophenone . .
5-Thio-t-butylvalerophenone .
5-Thiophenylvalerophenone .

6-Thiobutylhexanophenone . .
3-Butylsulfinylpropiophenone
4-Butylsulfinylbutyrophenone
5-Butylsulfinylvalerophenone
5-Phenylsulfinylvalerophenone
3—Butylsulfonylpropiophenone
4—Butylsulfonylbutyrophenone
5-Buty1sulfonylvalerophenone
5-Phenylsulfonylvalerophenone
2-Methylsulfinylacetophenone
2-Methylsulfonylacetophenone
5-Thioacetoxyvalerophenone .

5-Thiocyanatova1erophenone .

trans-4-Chloro-l,4-dimethyl-1-benzoyl-

cyclohexane . . . . . . .

cis- and trans-4-Bromo-1,4-dimethyl-l-

benzoylcyclohexane . . . .

4'-Methoxy-5-chlorovalerophenone

4'-Trifluoromethyl-5-chlorovalerophenone

5-Iodovalerophenone . . . . .

5—(4'-Methoxy)-phenoxyvalerophenone .

4-Benzhydryloxybutyrophenone

ix

Page
128
129
129
129
129
129
129
130
130
130
130
131
131
131
131
131
132
132

132

133
134
134
134
134

135

Page
Techniques . . . . . . . . . . . . . . . . . . . 135
Preparation of Samples . . . . . . . . . . . . 135
Photochemical Glassware . . . . . . . . . . 135

Stock Solutions and Photolysis Solutions . . 136

Quantum Yields, Quenching, and Sensiti-
zation Studies . . . . . . . . . . . . . 136

Degassing . . . . . . . . . . . . . . . . . 136
Irradiation Procedures . . . . . . . . . . . . 137
Kinetic Runs . . . . . . . . . . . . .°. . 137
Preparative Runs . . . . . . . . . . . . . 137

Analysis of Samples . . . . . . . . . . . . . 137
Identification of Photoproducts . . . . . . 137

Gas Chromatography Procedures . . . . L . . 140
Actinometry and Quantum Yields . . . . . . 141

Spectra . . . . . . . . . . . . . . . . . . . 143

LIST OF REFERENCES . . . . . . . . . . . . . . . . . 147

APPENDIX 0 O O O O O O O O O O O O O O O O O O O O O 158

LI ST OF TABLES

Table Page
1. Photokinetic Data for Various Ketosulfides . . . 21
2 . Photokinetic Data for Various Ketosulfoxides . . . 24
3. Photokinetic Data for Various Ketosulfones . . . 25

4. Bimolecular Rate Constants for Quenching
by Sulfur . . . . . . . . . . . . . . . . . . 26

5. Calculated Rate Data for Sulfur Containing
Ketones O O O O O O O O O O O O O O O O O O 0 3 3

6. Relative Resonance Stabilization Factors
for Various Groups . . . . . . . . . . . . . 34

-7. Approximate Amounts of B—Cleavage Versus
y-Hydrogen Abstraction in a-Thioalkoxy-
acetophenones . . . . . . . . . . . . . . . . 40

8. Calculated Rate Data for a-Thioalkoxyaceto-
phenones . . . . . . . . . . . . . . . . . . 40

9. Quantum Yields and Rate Data for
p-Substituted Phenacylsulfides . . . . . . . 55

10. Quantum Yields and Rate Data for Structurally
Variant B-Benzoylsulfides . . . . . . . . . . 56

'k *
ll. Substituent Effects on n,n and n,w Transi-
tions in Phenacylsulfides . . . . . . . . . . 58

12. Triplet Energies of Ring-Substituted
Phenacylsulfides . . . . . . . . . . . . . . 59

13. Approximate Percentage of IBP and MAP Found
in the Photolysis of t-ZSPh . . . . . . . . . 74

14. Calculated Rate Data for Various Phenacyl-
sulfides . . . . . . . . . . . . . . . . . . 80

15. Relative Rates of B-Cleavage in Phenacyl-
sulfides . . . . . . . . . . . . . . . . . . 83

xi

Table

16.

17.

18.

19.

20.

21.

22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.

Quantum Yields of Acetophenone and 4-Benzoy1-

1-Butene Formation from Various
G-Substituted Valerophenones . . .

Solvent Effects on B-Cleavage for Various

S-Chlorovalerophenones . . . . . .

Quantum Yields and Rate Data for 4-Halo-l,4-
Dimethyl-l-Benzoylcyclohexanes . .'

Rate Constants of B-Elimination of Various
Substituents in G-Substituted Valero-

phenones O O O O O I O C I O O I 0

Rate Constants of y-Hydrogen Abstraction and
a-Cleavage for the 4-Halo-l,4-Dimethyl-l-

Benzoylcyclohexanes . . . . . . .

Ground State Equilibria of 4-Halo-1,4-

Dimethyl-l-Benzoylcyclohexanes . .

Data for 2-Thiomethylacetophenone

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

for
for
for
for
for
for
for
for
for
for
for
for
for

for

Thio—t-butylacetophenone
2-Thiobutylacetophenone .
4-Thiobuty1butyrophenone . .
4-Thio-t-butylbutyrophenone
4-Thiophenylbutyrophenone .
5-Thiobutylva1erophenone . .
5-Thiophenylvalerophenone .
6-Thiobuty1hexanophenone .
5-Thiocyanatova1erophenone
5-Thioacetoxyvalerophenone .
2-Methylsulfinylacetophenone
4-Butylsulfinylbutyrophenone
5-Buty1sulfinylvalerophenone

2-Butylsulfonylacetophenone

xii

Page

93

94

95

108

115

118
160
160
161
161
162
162
163
163
164
164
165
165
166
166

167

Table
37.
38.
39.
40.
41.
42.
43.
44.

45.

46.

47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.

58.

59.

Data

Data

Data

Data

Data

Data

Data

Data

Data

for
for
for
for
for
for
for
for

for

5-Butylsulfonylbutyrophenone . .

5-Butylsulfonylvalerophenone . . . .
2-Thiophenylacetophenone . . . . . .
2-Thiophenyl-4'-F1uoroacetophenone .
Thiophenyl-4'-chloroacetophenone . .
2-Thiopheny1-4'-bromoacetophenone .
2-Thiophenyl-4'-methy1acetophenone .
2-Thiophenyl-4'-methoxyacetophenone

2-Thiophenyl-4'-thiomethoxyaceto-

phenone . . . . . . . . . . . . . . . . .

Data for 2-Thiophenyl-4'-dimethy1aminoaceto-
phenone . . . . . . . . . . . . . . . . .

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Solvent Effects on Quantum Yield for 5-Chloro-

for
for
for
for
for
for
for
for
for

for

2-Thiophenyl-4'-phenylacetophenone .
2-Thi0phenyl-4'-cyanoacetophenone .
2-Thiophenylpropriophenone . . . . .
2-Thiopheny1isobutyrophenone . . .

l-Thiophenyl-l-benzoylcyclopropane .
4'-Thiophenylmethylacetophenone . .
4'-Thiophenylacetophenone . . . . .
Phenyldesylsulfide . . . . . . . . .
5-Phenylsulfinylvalerophenone . . .

5-Phenylsulfonylvalerophenone . . .

valerophenone . . . . . . . . . . . . . .

Solvent Effects on Quantum Yield for 5-Chloro-

4'-methoxyvaler0phenone . . . . . . . . .

Solvent Effects on Quantum Yield for 5-Chloro-

4'-trifluoromethylvalerophenone . . . .

xiii

Page
167
168
168
169
169
170
170

171

171

172
172
173
173
174
174
175
175
176
176
177

177

178

178

Table Page

60. Data for trans-4-Chloro-l,4-dimethyl-l-
benzoylcyclohexane . . . . . . . . . . . . . 179

61. Data for trans-4-Bromo-l,4-dimethyl-l-
benzoylcyclohexane . . . . . . . . . . . . . 180

62. Data for cis-4-Bromo-l,4-dimethyl-l-
benzoylcyclohexane . . . . . . . . . . . . . 181

63. The 3-Thiobutylpropiophenone Sensitized
Isomerization of cis-l,3-pentadiene . . . . 181

64. The 4-Thiobutylbutyrophenone Sensitized
Isomerization of cis-l,3-pentadiene . . . . 182

65. The 3-Butylsulfinylpropiophenone Sensitized
Isomerization of cis-1,3-pentadiene . . . . 182

66. The 3-Butylsulfonylpropiophenone Sensitized
Isomerization of cis-l,3-pentadiene . . . . 182

xiv

LIST OF FIGURES

Figure

l. Stern-Volmer Quenching Plot for Acetophenone
Formation from 4-SBu (O) , 4-StBu (.) ,
and 4-SPh ([5) in Benzene with 1,3-
pentadiene . . . . . . . . . . . . . . . .

2. Quenching of Acetophenone Formation from Butyro-
phenone with BuSBu (A) , BuSOBu (.) , and
BuSOzBu ([3); Quenching of p-MeO Valero-
phenone with BuSOBu (A) and BuSOzBu (Q) . .

3. Dependence of uantum Yield for 3-SBu (C))
and 4-SBu ( ) Sensitized Isomerization
of cis-1,3-pentadiene on Diene Concen-
tration in Benzene . . . . . . . . . . . .

4. Hammet Plot of Relative Rates of Triplet State
Y-Hydrogen Abstraction for G-Substituted
ValerOphenones. (Points Cl and CN are
included for comparison and can be found
in reference 76.) . . . . . . . . . . . . .

5. Quantum Yield of Acetophenone Formation in
2-SPh Versus [¢SH] . . . . . . . . . . . .

6. Stern-Volmer Quenching Plot for the Quenching
of the p-Substituted Acetophenone Forma-
tion from Cl-ZSPh (O), Br-ZSPh (Q),
Me-ZSPh (A), and CN-ZSPh (A) with
Napthalene in Benzene . . . . . . . . . . .

7. Ultraviolet Spectra of 2-SBu. [A = 0 . 00183M(EtOH) ,
B = 0. 0014M(heptane) , C = 0. 000183M(EtOH) ,
D==0.00014M (heptane)] . . . . . . . . . .

8 . Phosphorescence Spectrum of 2-SBu in MTHF at 77K .

9 . Phosphorescence Spectrum of 2-SPh in MTHF at 77K .

lO. Phosphorescence Spectrum of OMe-ZSPh in MTHF
at 77K 0 O O O O O O O O O O O O O O O O O

XV

Page

27

28

29

37

60

61

62
63
64

65

7

Figure Page

11. Phosphorescence Spectrum of NMez-ZSPh
in MTHF at 77K . . . . . . . . . . . . . . 66

12. Phosphorescence Spectrum of CN-ZSPh in
MTHF at 77K 0 I O O O O O O O l O O O O O O 67

13. X-Ray Crystal Structure of trans-CDMBC . . . . 96

14. NMR Spectra of trans—CDMBC in CDCl

(Bottom);
in cnc1 Containing 0.0259g/o.5%1

Eu(fod)§(Top) . . . . . . . . .

. . . . . 97
15. NMR Spectra of trans-BDMBC in CDCl

(Bottom);
in cuc1 Containing 0.0259g/o.531

Eu(fod)g(Top) . . . . . . . . .

. . . . . 98
16. NMR Spectra of cis-BDMBC in CDCl3 (Bottom);
in CDCl Containing 0.0259g/0.5ml

Eu(fod)§(Top) . . . . . . . . . . . . . . . 99

17. Temperature Dependence of qu for Valero-
phenone (‘) and 6-Iodovalerophenone (A)
in Benzene . . . . . . . . . . . . . . . . 100

18. 13C Spectrum of trans-CDMBC in CHCl3 . . . . . 144
19. 13C Spectrum of trans-BDMBC in CHCl3 . . . . . 145
20. 13C Spectrum of cis-BDMBC in CHCl 146

3 . . . . . .

xvi

Scheme

1.

LIST OF SCHEMES

The Mechanism of the Norrish Type II
Reaction 0 O O O O O I O O O O O O O O 0

Available Pathways for the Biradical Formed
from a-Cleavage . . . . . . . . . . . .

Photolytic Cleavage of Pivalophenone . . .

Photochemical Fate of l-Methyl-l-Benzoyl-
cyclohexane . . . . . . . . . . . . .

Mechanism of B-Cleavage of B-Ketosulfides .
Addition of Thiols to Vinylcyclopropane . .

Synthesis of 4-Halo-l,4-Dimethyl-l-
Benzoylcyclohexanes . . . . . . . . . .

Photolysis of 5-Thiophenoxyvalerophenone in
Benzene . . . . . . . . . . . . . . . .

Conformational Effects in the Photochemistry

of trans-CDMBC . . . . . . . . . . . . .

xvii

Page

10
10

12
68
73

86

105

116

INTRODUCTION

Objectives and Organization

 

The original objective of this thesis was, in a broad
sense, to investigate structure-reactivity relationships in
organic photochemistry. In particular, the effect of chain
length upon the rate of intramolecular charge-transfer
quenching of the excited benzoyl group by various sulfur
moieties was to be investigated. However, as work progressed,
unexpected results provided the stimuli to stray away from
the original objective and pursue other paths. Thus, this
thesis is composed of two separate but related parts. In an
attempt to avoid duplication, the introduction is composedcnf
one part in which topics relevant to the problems investi-
gated will be discussed. The results for each part are
treated separately and the corresponding discussion follows
each section. The experimental section presents the proce-
dures and materials for both parts.

Part I deals solely with the effect of chain length
upon the rate of quenching of the benzoyl group by various
sulfur moieties. In particular, ketosulfides, sulfoxides,

and sulfones were investigated.

Part II deals with radical B-cleavage of halo and
thiyl radicals both from excited states and photogenerated
biradicals. This includes the photochemistry of phenacyl
sulfides, 5-halo enui 5-thiyl substituted valerophenones,

and a novel cyclic system.

The Norrish Type II Reaction

Ketones possessing y-hydrogens undergo a charac-
teristic 1,5-hydrogen transfer, followed by cleavage or
cyclization, upon uv irradiation. Norrish and Appleyard1
first observed this reaction in 1934 while investigating
the photodecomposition of methyl butyl ketone in the gas
phase. Yang,2 who first noted the formationxxfcyclobutanols
as products, hypothesized the intermediacycxfa 1,4 biradical.
Compelling evidence for the intermediacy of a 1,4 biradical

4 In fact, the bi-

has been presented by Wagner3 and others.
radical from y-methoxybutyrophenone has actually been trapped
by thiols.5 The formation of cleavage products and of
cyclobutanols is collectively called the Norrish Type II
Reaction. Scheme 1 presents the accepted mechanism.

For phenyl alkyl ketones the rate constant of inter-

11 -1

system crossing, k isr~10 sec ;so fluorescence, kf,

isc’
which occurs on the order of 106sec-l, and radiationless
decay, kd, are negligible. As a result, the intersystem
crossing yield is equal to unity in most cases.6 Thus,1flua

triplet manifold is responsible for the majority of the

photoreactivity observed in phenyl ketones. Population of

 

 

 

 

 

 

R
J

Scheme 1. The Mechanism of the Norrish Type II Reaction.

the triplet manifold results in y-hydrogen abstraction
followed by either reverse hydrogen transfer, k_Y,cn:product
formation, kcyc and k3. Reverse hydrogen transfer was first
postulated by Hammond and Wagner7 to account for low quantum
yields i3: systems where the excited state reactivity was
thought to be fairly high. Wagner8 later showed that reverse

hydrogen transfer could be eliminated by the use of polar

solvents or various additives that are good Lewis bases.

Phosphorescence, k from the triplet is slow relative to

p’
y-hydrogen abstraction and is usually insignificant.

The reactivity of the triplet benzoyl group has been
likened by Walling and Gibian9 to that of the t-butoxy
radical. Numerous studies investigating structure-reactivity

relationships have been presented by Wagnerlo 11

and others,
but in general the variation in reactivity in phenyl ketones
can be ascribed to either inductive or resonance effects on
the y-radical center or the nature of the excited triplet.
Electron releasing substituents on the benzene ring
generally lead in) decreased or negligible reactivity of the
triplet benzoyl due to the interposition of a 3n,n* state,
which is unreactive toward y-hydrogen abstraction.12
Interestingly, Wagnerl3 has shown that thermal equilibration
of the 3n,n* state with the higher 3n,n* state in p-methoxy-
valerophenone is taking place. In this case, the low equi-
librium concentration of the upper 3n,n* state produces a
low observed rate constant for y-hydrogen abstraction.
Little work concerning the effect of structure on
cleavage:cyclobutanol ratios has been done, but Lewis14 has
shown that a-substitution on phenyl alkyl ketones markedly
15

increases the amount of cyclization. Wagner has noted an

analogous effect for a-fluoroketones.

Charge-Transfer

 

The phenomenon of charge-transfer was first invoked

by Mulliken16 to explain why iodine is violet in CCl but

4

brown in benzene. Formally, one can envision charge-transfer
as simply partial electron transfer from a donor to an

acceptor.
D°°+ A' -—+ D'+A‘(C-T complex)

Photochemical precedent was established by Leonhardt

17

and Weller who demonstrated by flash spectroscopy that

solutions of perylene and an amine undergo electron transfer,

18 later

a process not possible in the ground state. Cohen
observed that benzophenone isphotoreduced by Et3N 1000 times
faster than by isopropanol. This led to the suggestion that
rapid electron transfer from the nitrogen to the triplet
carbonyl followed by proton transfer was responsible for the

19 later suggested the

observation. Davidson and Lambert
following mechanism for the photoreduction of benzophenone

by amines.

+ - -
2NCHZR) -—> R COH + RCHNR

* u o _
R c=o 3 + RCH NR ——a (ch-o R 2 2

2 2 2

Later experiments by Cohen and Chao20

definitively ruled out
direct hydrogen abstraction from the amine.

The ionization potentials of amines have been correlated
with their ability to interact with triplet ketones. Cohen and

21

Guttenplan noticed an inverse relationship between the

ionization potential of the amines and their abilitytxnphoto—
reduce a ketone. However, they noticed the results were
inconsistent with full electron transfer and could best be

described as partial electron transfer. The fact that small

6

solvent effects were noted, relative to those for ground
state electron transfer reactions, further supported
their contention. Wagner and Kemppainen22 also noted no
increase in the rate of quenching of valophenone by tri-
ethylamine or t-butylamine in CHBCN relative to that in
benzene.

Other types of heteroatoms have demonstrated the
ability to form C-T complexes with excited carbonyls. Thio-
ethers have been shown to quench the phosphorescence of
benzophenone and also its photoreduction by isoborneol.23
Interestingly, little photoreduction by sulfides possessing
a-hydrogens was found to occur, indicating that proton trans-
fer analogous to that observed for amines24 is not an
important pathway for sulfides. The 4-carboxybenzophenone
sensitized photooxidation of methionine was found to occur
by initial charge-transfer complexation between triplet
benzophenone and sulfur followed by internal electron transfer
to nitrogen.25

Phosphorous, antimony, and arsenic have also been
postulated to quench the Type II Reaction of butyrophenone
via a charge-transfer interaction.26

Intramolecular charge-transfer quenching has not been
extensively investigated. However, Wagner27 has found that
intersystem crossing yields decrease and rates of quenching
increase as an amino group is moved closer to the carbonyl.
These facts indicate a competition between intersystem

crossing, charge-transfer quenching, and y-hydrogen abstrac-

tion. Type II products have also been shown to arise from

the C-T state of y-dimethylaminobutyro-2-napthone by
‘protonation of the ketyl radical anion.28

Strict conformational requirements for C-T quenching
were demonstrated by Wagner and Scheve.29 The lack of C-T
quenching in 1:3 demonstrates that such quenching requires

through-space orbital overlap.

Ph

[.1
I
(D

Intramolecular charge-transfer quenching of excited
ketones with sulfur has not been previously measured.

However, a "C-T type" intermediate has been proposed for

the photorearrangement of 2 to 3.30

<35$®~©é~<§

A variety of optically active sulfoxides have been

shown to undergo photochemically induced stereomutation,

31

resulting in racemization. The charge-transfer nature of

these transformations is indicated by the fact that energy

transfer would be at least 10-15 kcal endothermic.32

Sulfones have not been previously shown to interact

with excited carbonyls, but the conversion of 4 to 5 hints

at some sort of direct interaction.33

63;“ V I
v o
802 r1-—L—_> Pry/H h

i .5.

Energy Transfer

 

Other mechanisms besides C-T interactions are possible
for the quenching of triplets. When an acceptor has a lower
triplet energy than the donor, triplet-triplet energy transfer
occurs. Other types of energy transfer are possible, but in
the case of phenyl ketones, intersystem crossing yields are
usually high so triplet-triplet energy transfer predominates.
Usually, the effectiveness of a quencher is determined by
the position of its lowest triplet level and not by its molec-
ular structure.34 On the other hand, the rate of exothermic
triplet energy transfer in solution is dependent on the
viscosity of the solvent, which for moderately viscous

solvents is described by the modified Debye Equation.35

k = k

et diff = 8RT/2000n

However, in less viscous solvents the quenching rate constant

is still lower than the calculated diffusion rate. The

implication of this is that there is inefficiency in the

energy transfer which may be indicative of a preferred

configuration of the donor and acceptor molecules.
Interestingly, not much is known about the steric

requirement to promote the exchange interaction needed for

transfer; however, Wagner and McGrath36 have shown that

transfer is rapid at van der Waals separation of donor and

37

acceptor. Cowan and Baum have measured ke in styryl-

t
ketones where the separation between donor and acceptor

varies from 2 to 4methylene groups. Predictably, when

11 M-1 -1

n = 2, ke =~lO sec . As n is increased to 4,

t
1 -1

k = ~109 M- sec . Thus, the number of conformations in

et
which the two ends of the molecule interact decreases
rapidly as the number of methylene groups is increased. It
has been estimated that for every 1.23 increase in the
distance between the donor and acceptor, an order
38

of magnitude decrease in ket results.

The Norrish Type I Reaction, a-Cleavage

 

The Norrish Type I Reaction involves homolytic
cleavage of the 1,2 bond in cyclic and acyclic ketones,
resulting in the formation of an acyl and alkyl radical pair.
Many other classes of compounds, such as the carboxylic acid

derivatives,39

which possess a heteroatom as the a-substituent,
also undergo this reaction. Thus, the reaction will be
referred to, in a broader sense, as a-cleavage. The fate

of the radical pair varies depending largely on structural

10

40 but the three possible routes as pictured in

features,
Scheme 2 are recoupling, two modes of disproportionation,

and decarbonylation.

R
H/CM

. hv C ROH /\/\/fi\0
-————9 ‘__9W/”\v/A\C:CJO'_—€> R
§_____

\

Scheme 2. Available Pathways for the Biradical Formed from
a-Cleavage

CC) + ,/”\»/”\3

In phenyl ketones, a-cleavage leads to a slightly different
picture than that presented in Scheme 2. As shown below in
Scheme 3, the photolysis of pivalophenone41 results in the
formation of a benzoyl radical and a t-butyl radical. In-cage

radical-radical recombination competes effectively with

\\:SH
Ph/ji\H + ,/'_' coupling Ph/I

products +

H_<_

Scheme 3. Photolytic Cleavage of Pivalophenone.

ll

diffusion out of the cage. Disproportionation to form
benzaldehyde and isobutylene can occur in-cage or out-of—cage.

However, in the presence of thiols, which are efficient

42

radical scavengers, the intermediate radicals are trapped,

thus minimizing or eliminating out-of—cage disproportionation
and coupling.

While a-cleavage is the major mode of decomposition

43

for certain aliphatic ketones, it is usually not observed

for normal phenyl alkyl ketones. Even in a,a-dimethylvalero-

phenone, Y-hydrogen abstraction is sufficiently fast that

a—cleavage comprises only about 5% of the reactivity.44 In

fact, triplet aliphatic t-butyl ketones a-cleave about 4000

45

times faster than triplet pivalophenone. The nature of the

excited state has also been found to greatly influence the

46

rate of a-cleavage. Lewis has shown that pivalophenone,

*
which has a lowest 3n,n state, cleaves with a rate constant

of around 107'sec-l; but p-phenylpivalophenone, which has
*

a 3n,w lowest triplet, is essentially stable to photolysis.
Lewis47 has noted a competition between a-cleavage and

y-hydrogen abstraction in some very elegant work with several
cycloalkyl phenyl ketones. Scheme 4 presents the conforma-
tional possibilities for 1-methyl-l-benzoylcyclohexane (6)
-Interestingly, 6:3 only undergoes y-hydrogen abstraction,

whereas 6-e exhibits only a-cleavage. In this case, kII and

kI were faster than interconversion of the excited conformers,
so product ratios reflected the ground state population of
the respective conformers. Thus, Lewis determined that the

ground state equilibrium was about 65:35 in favor of 6-e.

12

 

 

 

 

Type II products Type I products
A A)
kII kI
3 o 3 o
Kax Keq
At It
‘c
‘,R
___9 P
4___
Ph
6-a 6-e

Scheme 4. Photochemical Fate of l—Methyl-l-Benzoylcyclo-
hexane.

B-Cleavage

 

There is a wide variety of photochemical reactions of
carbonyl moieties in which electronic excitation results in

initial cleavage of one of the bonds 8 to the carbonyl

group.48 Also typical are B-eliminations in free-radical

49

reactions. In fact, a-haloacetophenones and, to a lesser

extent, phenacylsulfides have been used to photoinitiate

50

polymerization reactions. To date no kinetic studies on

B-cleavage reactions of ketones have been done.

13

There are, however, several interesting photoreactions

involving B-elimination. The photoisomerization of

. . . . 5
isothiochroman-4-one IS a c1a531c example. 1

We... 0‘,

W

O .
l o
//
.<————
co;—

Surprisingly, when the benzene ring is replaced with a

 

 

 

napthalene, the reaction does not go.

The photolysis of 1 yields 8 by B-cleavage of oSPh
followed by disproportionation and aromatization.52

0

¢ hv -S¢

 

O

|\l

(D
\l
+

OH

00

 

H89?)

8

[CD

14

53,54

In other systems, where disproportionation is not

possible, coupling products are observed as shown below.

0| R L '0' H + sulfur containing
Ph/b\/s\ PM?) prOdUCtS

 

o v o
/°\/S‘>2’r “ > AVA + i—som”

The formation of the vinylsulfonate in the second example
arises from radical recombination on oxygen rathertflunicarbon

as shown below.

[Asa/R] + - ---e +

15

Stern-Volmer Kinetics

The quantum yield for any photochemical process can be
expressed as a product of probabilities. Thus, for the

Type II Reaction:

in = c) (1)

1.
?-k+kd (2)

where ¢isc equals the intersystem crossing yield, kY equals
the rate constant of hydrogen abstraction, kd equals the rate
constant of triplet decay, T equals the triplet lifetime, and
P equals the probability that the diradical will go on to

product. In the presence of an external quencher, GD becomes:

= kY + kd + kq[Q] (3)

all-4

where kq equals the bimolecular rate constant. Utilizing

these facts, the Stern-Volmer Equation (4)55 can be derived.

0
= 1 + qu [Q] (4)

9+9

In the presence of polar solvents or Lewis bases,
which minimize reverse hydrogen transfer, the maximum quantum

yield can be expressed:

(5)

Thus,

k = (6)

 

16

The sensitization equation (7)56 allows measurement

Of ¢isc°

-1 -1 -1 1

sens. - isc ktr[Q]) (7)
Thus, in the case of 1,3-pentadiene, a equals 0.55 and a
plot of 0.55/q)c+t versus [cis-l,3-pentadiene]-l yields a
straight line in which the reciprocal of the intercept equals

¢isc and intercept divided by the slope equals ktTr°

PART I

INTRAMOLECULAR CHARGE-TRANSFER QUENCHING OF EXCITED
STATES BY SULFUR ‘

Results

Preparation and Product Identification

A variety of ketosulfides of varying chain length were
prepared by Sn2 displacement on an appropriate haloketone by
the corresponding sodium thiolate. The ketosulfoxides and
sulfones were prepared by hydrogen peroxide oxidation of the
corresponding ketosulfides. The corresponding compounds and
their abbreviations are listed in Tables 1, 2, and 3. For
example, a-thiomethylacetephenone is denoted as 2-SMe and
a-methylsulfinylacetophenone as 2-SOMe.

All compounds except 3-SBu, 3-SOBu, and 3-SOzBu pro-
duced acetophenone upon uv irradiation. These compounds were
stable to irradiation at 31303 and underwent no disappearance
of ketone. Acetophenone was actually isolated by preparative
vpc for 4-SBu but was subsequently identified either by the
appearance of a singlet at 2.36 in the nmr or by comparison
of its vPc retention time with that of an authentic sample.
The olefinic moiety which results from cleavage was not
observed since it probably came out under the solvent peak

on the vpc. Small peaks which were assumed to be the

17

18

cyclobutanols were sometimes observed and usually corres-
ponded to about 10-15% of the total product. No evidence of
the corresponding thietanols was observed for 2-SMe and
2-SBu.

The 6-substituted valerophenones were found to produce
varying amounts of 4-benzoy1-l-butene (4-BB) in addition to
acetophenone. The mechanism for the formation of 4-BB will

be discussed in Part II.

Quantum Yields

Quantum yields for acetophenone formation and other
products were determined by irradiation at 3130A in a merry-
go-round apparatus at 25°C. Solutions containing 0.05M
ketone in benzene, which sometimes contained various addi-
tives, were irradiated in parallel with degassed benzene
solutions of 0.1M valerophenone, which served as an acti-
nometer.57 All samples were degassed by two or three freeze-
thaw cycles prior to irradiation. Percent conversion of the
ketone and/or actinometer was kept below 10% whenever
possible. Disappearance quantum yields were measured at
typically 20-30% conversion. Product to standard ratios were
measured by vpc. The associated error was estimatedtnrdupli-
cate runs and was generally found to be about i5% for aceto-
phenone formation and about :10-15% for disappearance quantum
yields.

Polar solvents or Lewis base additives had little

or no effect upon the quantum yields. The maximum quantum

19

yields, ¢ I were usually obtained in benzene containing

max
1.0M dioxane. The quantum yields are listed in Tables 1,

2, and 3.

Quenching Studies

 

‘Stern-Volmer quenching slopes were performed at 3130A
or 36603 by photolysis of 0.05M ketone solutions containing
varying amounts of either 1,3-pentadienecnzl-methylnapthalene.
Conversions were usually kept below 10% for the tube with no
quencher, and the slopes were linear outtx>a ¢°/¢ value of
about 7 or 8. The associated error was estimated by dupli-
cate runs to be about i10%. Values obtained from these
studies are listed on Tables 1, 2, and 3. A representative
Stern-Volmer plot is presented in Figure 1.

The bimolecular rate constants for quenching by
n-butylsulfide, n-butylsulfoxide, and n-butylsulfone were
determined by an analogous procedure through the utilization
of butyrophenone and p-methoxybutyrophenone as substrates.
No quenching of acetophenone formation was detected when
n-butylsulfone was used as a quencher. The bimolecular rate
constants are listed in Table 4, and the quenching plots are

presented in Figure 2.

Intersystem Crossing Yields

 

Intersystem crossing yields were determined by
parallel irradiation at 31303 of 0.05M ketone solutions

containing varying amounts of cis-1,3-pentadiene and a 0.10M

20

acetophenone solution containing 1.0M cis-l,3-pentadiene,

58 Plots of reciprocal

the latter serving as an actinometer.
quencher concentrations were linear. In all cases where

measurement was possible, ¢. was equa11x31. Irreproducible

isc
results were obtained for the a-thioalkylacetophenone and the
G-substituted valerophenones due probably to the production

of low concentrations of radicals. The intersystem crossing

yields are presented in Tables 1, 2, and 3, and a representa-

tive sensitization plot is presented in Figure 3.

21

Anmumuec
%m>\/U\nm

 

 

 

m~.m
me.H o.H s~.o uuu nu- a
Asmmuec
mo.m m.eoa.e amm\\/(\)/AV\:E
o~.o n oe.a o.H He.o n mH.e mH.o H~.o a
Asmmumc
smm//\\/4v\nn
mom.o n OH.H o.H In- In- nu- m
Asmmnmc
umo.o n mm.o emm\//o\HE
H.o n e.H nu- mo.o n me.o me.o so.o n me.o a
Asmumumc
Jx/m\\//o\xrw
v.0 n m.m nu: umoo.o n eo.o Hoo.ov nu- :
o
Amzmnmv
omo.o n mm.o mzmx\/xw\en
~.o n eo.m In- mm.o In- He.o a
cox one 539 e VT e 9509.50
3 m
.mmowwdumoumx m50aum> How sumo owumcflxouonm .H manna.

22

 

.ommumv
Oflm//\\/(\// m

 

Redo.o _
+ as us. mas o mm o nu- o
Azomsmc
m N . 0 20m <</W\£m
sea -n- oo.o emu o I). m
xsmmnmc
mo.oe smm.\)/\\//\\/Ax\:m
e.em o.H Ho.o n m~.o Ho.o n m~.o sm.o a
Annmumv
nm~.o nm~.o namI/\\/<\)xw\en
m.mm In- mao.o mHo.o In- a
Anmmumv
Hoo.o n eoo.o :mm//\\//\\/Aw\en
m.e~ nu- Ho.o n fi~.o mH.o m~.o a
Annalee
nmm\\/(\)/o\xrm
oe.o es.e o.H No.o H em.o No.0 n mm.o nu- a
x on A.” e axmae m 9 Mia 9:59:00

 

 

A.U.ucoov .H OHQMB

23

.mc0psnlanahoNconlv:

.uoHQ Hoooumwoou mandoo Eoum pmcamuno osam>m

.po>uomno mcoumx mcfluumum mo mocmumommomflp ozm

.ocmucon :H ocwpwuhm 2o.Hm

.ucm>aom Hocmnumzo

.ocmncon ca mme 2mo.oo

.mcoucon cw ocmxoflp So.an

.MOMHM Um QCGNGQQ C.“ GCOCGSQOUQUM HO COHHMEHOH 05v... HON mmVHmflxn SUCMSOM

 

A.e.ueooc .H manna

24

.mcmusnlanahoNcmnlvo

.mcaeensn zom.oe

.mme ch.oo

.mcmxoflp Zo.Hn

.momam um ocmncon cw poumwpmuuHm

 

 

AsmOmumc
mmm.o 9m _ m
o.nmo.o H mm.o owl/\)/(\)/J\LL
~.o n N.H~ in- nme.c mo.o mm.o r
Asmomuev
emmo.o smom\/\\/o\HE
om.o n e.mH o.H nmo.o mo.o us: a
Asmomnmv
o~.o n oe.a o.H nu- In: In- a
Asmuomumc
. - . . prom\\//J\irm
nu- nu- oeo o + mm o ma 0 u)- w
Amzomumc
mzom>o\;m
no.0 n ma.o u)- ome.o n ee.o HH.o u)- a
v one xms ml
p x e e Q.Me e panomfioo

 

 

.mmpflxOMHSmoumm msoflum> MOM sumo owumcflxouonm .m manna

25

.ocmusnlalahoNconlv

@

.mcmeMp 2o.Ho

.mcmucmn :H mme Smo.o

Q

.Momam um mcmucmnfijncwumflomuuHm

 

 

 

 

Annmom-mc
N
am On
e.o~oo.o n mo.e /\/<\/o\§H
me n mom I.) one.o n oe.o nu: me.o :
o
Asmmomnec
- sm~0m\\/(\)/AW\:E
ems + omsm o H oom o uuu nu: a
Aammomumv
. In- In- nu- , _
was o H o
omumv
nu- nu- has e me o u-) r
AsmNOmnmv
I DMN0m>U\Sm
as + saw I-) nem.o om.o nu- :
0
sex ones xmee we sue easoneoo
.mmc0mazmoumx msowum> MOM mama owuocwxouonm .m manna

26

Table 4. Bimolecular Rate Constants for Quenching by Sulfur.

 

 

 

Quencher kq’lOSMIlsec-l
n-butylsulfide 3.25a
n-butylsulfoxide 0.014a

0.012
c

n-butylsulfone ---

 

aMeasured by quenching the formation of acetophenone from
butyrophenone.

bMeasured by quenching the formation of acetophenone from
p-methoxyvalerophenone.

cNo quenching of acetophenone formation from butyrophenone or
p-methoxyvalerophenone observed.

27

 

 

6‘
1k
5..
4‘
A.
¢O
I
3-
A.
2 ‘ (5
6
0
1.
0.5 1.0 1.5 2.0

[l,3-pentadiene],M

Figure 1. Stern-Volmer Quenching Plot for Acetophenone
Formation from 4-SBu (O), 4-StBu (O), and 4-SPh(A)
in Benzene with 1,3-pentadiene.

e|e

Figure 2.

 

28

)4

 

 

A»
.A
ea A9 2%—
0.5 1.0 1.5 2.0

[Q] .M

Quenching of Acetophenone Formation from Butyro-
phenone with BuSBu (A), BuSOBu (7.) , and
BuSOZBu(Z§);and Quenching of p-MeO Valerophenone
with BuSOBu (‘) and BuSOZBu(@) .

 

 

29

 

Figure 3.

*O
*0
O
'3
—l I r I I I
0.5 1.0 1.5 2.0 2.5 3.0

[cis-pentadiene]"':",M"l

Dependence of Quantum Yield for 3-SBu (D) and
4-SBu (.) Sensitized Isomerization of cis-l,3-
pentadiene on Diene Concentration in Benzene.

30

Discussion

General Observations

 

As indicated in Tables 1, 2, and 3, the quantum effi-
ciencies for acetophenone formation are fairly low, typically
5 around 20-30%. Normally, in the absence of alternative decay
routes the inefficiency in the Type II Reaction is due to

9 In the

revertibility (reverse 1,5-hydrogen transfer).5
present system, however, only a modest increase in quantum
yield is observed in the presence of additives (e.gu,jpyridine
or dioxane) which normally maximize the Type II yield. For
example, 4-SBu goes from a quantum yield of 0.13 in benzene
to only 0.18 in benzene containing 1.0M dioxane. Generally,
enhancements by a factor of 2-3 are observed. Thus, intra-
molecular hydrogen bonding between the ketyl and sulfur

moieties must be faster than reverse hydrogen transfer

H-bonding >> k-x) '

H
Ph’g;v;T/SR k . PW’Cf .
H-bonduEL \
o *7 ' \
hv
Type II
E:\\N #:2é: products
0 R
M
P

Such intramolecular hydrogen bonding has been postulated previ-
60

(i.e., k

 

ously to explain the elimination of ROH in B-alkoxyketones .

31

Difficulty in maximizing the quantum yield has been noted
previously for 6-methoxyvalerophenone and was ascribed in
part to 6-hydrogen abstraction.61 The propensitycflfsulfides,
sulfoxides, and sulfones toward hydrogen bonding is well
documented;62 and as such, intramolecular hydrogen bonding
must be minimizing revertibility in the same manner as
external Lewis bases.63

Polar solvents seem to depress cyclization slightly
since solvation of the hydroxyl moiety presents some steric
inhibition to coupling.64 In contrast, analogous steric
problems are absent for intramolecular solvation; and, in
fact, an increase in cyclization might be expected since the
conformation necessary for intramolecular hydrogen bonding
favors that necessary for coupling. However, material
balances indicate that the normal amount of cyclization is
taking place, i.e., lO-20%. The anomalous lack of any
thietanol formation for 2-SMe and 2-SBu has been noted

65 . . .
and seems surprising Since the analogous com-

previously
pounds containing oxygen or nitrogen cyclize with ease.66

Ground state reversion of the initially formed thietanol to
starting material can be accommodated by two pathways; and

as such, isomerization of the starting materials would be

expected as shown below.

H
% '9 2 88
Ph 8 ——)ph/C\/S\/RP S__9PP/C\‘/\

32

Since isomerization of starting material was not observed,67
this process can be eliminated. Therefore, it seems likely
the differing behavior of this system with respect to the
analogous oxygen and nitrogen systems may be related to

the relative weakness of the C-S bond (65 kcal) as compared
to the C-0 (85 kcal) and C-N (73 kcal) bonds. Also, the
interposition of the fairly large sulfur atom may introduce

subtle conformational effects, which inhibit cyclization.

Rate of Hydrogen Abstraction Versus Inductive
and Resonance Effects

 

 

Calculation of the various rate constants deserves
comment. The value of ky, the rate constant for y-hydrogen
abstraction, can be calculated from the measured lifetime
and the maximum quantum yield of Type II products according

to equation 6.

k = (6)

 

The calculated rate data is listed in Table 5. Now, in the
case of the a-thioalkoxyacetophenones, B-cleavage is found
to compete with y-hydrogen abstraction, so in these cases

the observed kY actually equals kY + k The extenttx>which

B'
B-cleavage competes in the thioalkoxyketones and the corres-
ponding corrections will be discussed in the following
section. The rate constant of C-T quenching will be

discussed in the appropriate section.

33

Table 5. Calculated Rate Data for Sulfur Containing Ketones.

 

 

 

Compound l,1085ec-l k lO-lsec-l k ,107sec-l
T Y’ ct
2-SMe 24.3 ---a 149
2-SBu 31.3 —--a 135
Z-StBu 12.8 ---a 118
2-SOMe 51.0 ---a 61.0
2-SOZMe 0.23 —--a 1.4
3-SBu 45.4 --— 455
3-SOBu 29.4 --- 294
3-SOZBu 0.28 --- 2.84
4-SBu- 29.4 52.9 241
4-SOBu 3.21 0.96 31.0
4-SOZBu 0.013 0.03 0.10
4-StBu 28.9 78.0 211
4-SPh 10.5 37.8 67.2
S-SBu 1.80 3.96 14.0
S-SOBu 2.36 9.91 13.7
5-sozau 0.24 1.01 1.42
S-SPh 1.30 3.89 9.09
6-SBu 1.37 3.42 10.2
S-SCN 0.47 1.2 3.5
S-SAc 1.14 9.15 2.28

 

aSee Table 7 for the separation of kY + k

B.

34

All substituents stabilize a radical center relative
to the unsubstituted case. The fact that the various kY values
vary greatly with substitution indicates that inductive deac-
tivation of the y-hydrogen center must be strong. In the
case of y-substitution, separationxmfthe competing inductive

68 has

and resonance effects is at best tricky; but Wagner
separated the two by assuming a p value of -4.3 for
y-substituents. Table 6 lists various relative stabilization

factors which were calculated using the data in Table 5.

Table 6. Relative Resonance Stabilization Factors for Various

 

 

 

Groups.

Substituent OI 10-4'3OI k/ko Stagiiiggtion
SPh 0.30 0.051 3.0 58.8
SBu 0.25 0.084 4.5 53.6
SOBu 0.52 0.0058 0.077 13.3
SOzBu 0.60 0.0026 0.022 0.78
OMe 0.30 0.051 5.0 98.0
Me --- --- 1.0 1.0
OH 0.25 0.085 3.1 37.0
0 0.10 0.37 3.1 8.4
O¢ 0.39 0.021 1.15 54.7

 

Table 6 reveals the following sequence listed in decreasing

ability to stablize an adjacent radical center:

OMe > SPh -SBu ~'O¢ > OH > SOBu > 0 > Me > 502Me

35

As with alkoxy radicals,‘59 the stabilizing effect of
y-substitution reflects the availability of the lone pair of
electrons. Ethers are about 2-5 times better than the
corresponding alcohols at stabilizing an adjacent radical
center. Qualitatively, it is known that sulfur can stabilize
a free radical since the a-hydrogens of sulfides are suscep-
tible to hydrogen abstraction.70 The present study indicates
a factor of about 2 less than the corresponding ether.
Interestingly, SBu and SPh stabilize an adjacent radical to
about the same extent, indicating a lack of participation
by the benzene ring. Although phenyl systems are known to
participate in free radical stabilization,71 ESR studies have
indicated no participation by the phenyl ring when attached
to a heteroatom.72 The stabilizing effect of a methyl group
is fairly small relative to heteroatoms as one might expect.
The difference in kY for a primary carbon versus a secondary
carbon, as in butyrophenone versus valerophenone, is about
16. However, a difference of about 2-0 between primary and
secondary is apparent for 2-SMe and 2-SBu. In the case of
y-methoxybutyrophenone versus y-methoxyvalerophenone, the

73

former is slightly more reactive. Here the greater reac-

tivity of a 3° relative to 2° carbon is not great enough to

offset the larger number of hydrogens in the latter. The

same effect has been noted for the a-alkoxyacetophenones,74

where the ky's for a-methoxy-auxin-ethoxyacetophones are

9 l 9

3.2- 10 sec- and 8.4 -10 sec-l, respectively--a factor of

2.6.

 

36

Introduction of an insulating methyl group as in the
d-substituted valerophenones corresponds to a decrease in
the inductive effect by a factor of 0.4375 and at the same
time eliminates any resonance stabilization of the y-radical
center. Figure 4 presents a Hammettgflrnzfor 6-substituents
in which a plot of log(k/k°), where ko equals the rate
constant of y-hydrogen abstraction for valerophenone, versus

76
0 yields a p-value of -l.85. Wagner has calculated an

I
identical p—value for various 6-substituents, and agreement
here indicates the correctness of the present values and
further illustrates the predictive value of such a plot.
However, an anomalous result arises in that 5-SOBu falls way
off the line and appears that y-hydrogen abstractionifisabout
ten times faster than that expected on purely inductive
grounds. An analogous activation has been noted for 6-Br
and 6-I valerophenone and was attributed to anchimeric
assistance in the hydrogen abstraction step.77 Comparable
rate enhancements have been observed previously for sul- I
fides,78 and Shevlin79 has recently observed a weak anchi-
meric effect by a sulfinyl group. Whereas assistance by

bromine or iodine and formation of a bridge species can be

pictured below,

37

 

 

 

0.0‘
A (8080)
-0.5'
k
log-é;
k
r
-1.0-
0.2 0.4 0.6 0.8
“’1
Figure 4. Hammet Plot of Relative Rates of Triplet State

y-Hydrogen Abstraction for 6-Substituted Valero-
phenones. (Points C1 and CN are included for
comparison and can be found in reference 76 . )

 

38

assistance by a sulfinyl group can be represented in two

ways:

0 R R

‘\S/’ .
.41 °r 1....

 

Unfortunately, only speculation concerning the nature of
anchimeric assistance by sulfinyl groups is possible with
the available data. The topic of anchimeric assistance will

be discussed in depth in Part II.

 

Competitive B-Cleavage and y-Hydrogen Abstraction

For the B-ketosulfides, sulfoxides, and sulfones,
B-cleavage is found to compete with y-hydrogen abstraction.
This reaction is well documented80 but has escaped a thorough
kinetic examination. Thus, 2-SBu has two available routes

for acetophenone formation as shown below.

diffusion
1) out of cage 9

R
[ p \. 'SBU ] 2)RSH 'Ph/o\+ BUSH

fl kBZ/‘SB

h
Ph/CVS\/\/ ‘b k H
\Y 6 3 Type II

P h/éVSW products

 

81 82
Lewis and Wagner have separately estimated that about:50%
of the initially formed radicals in Type [cleavage recombine

in-cage to form starting material as indicated. Thus,

39

compounds which form acetophenone primarily via B-cleavage
experience at least a 50% inefficiency. The addition of
thiols has been shown to increase the quantum yield of
product formation by trapping the radicals that diffuse out
of the cage.83 Enhancements on the order of two to five are
typical in the present system as well as previous systems.84
Examination of Tables 1, 2, and 3 allows estimation
of the amount of B-cleavage relative to y-hydrogen abstrac-
tion in the thioalkoxyacetophenones. For instance, 2-StBu,
which possesses no y-hydrogens, forms acetophenone in the
presence of 0.05M HSPh with a quantum yield of 0.04. Thus,
at least 4% of acetophenone formation arises from B-cleavage
in 2-SMe and 2-SBu. However, if one assumes about 50% in-
cage recombination, 8% of the light is attributable to
B-cleavage. If the total quantum yield of acetophenone is
divided into that found via B-cleavage, the competition
between B-cleavage and Y—hydrogen abstraction can then be
separated. The results are presented in Tables 7 and 8.

Interestingly, 2-SOMe and 2—SO Me appear to react mainly via

2
B-cleavage, which is in agreement with that observed by

85 86

Majeti and deMayo. A more detailed discussion of

B-cleavage appears in Part II.

40

 

 

 

 

 

 

 

Table 7. Approximate Amounts of B-Cleavage Versus Y-Hydrogen
Abstraction in a-Thioalkoxyacetophenones.
Com ound % B-Cleavage % y-Hydrogen
p Abstraction
2-SMe 21 79
2-SBu 14 86
2-SOMe 100 0
2-SOzMe 83 17
Table 8. Calculated Rate Data for a-Thioalkoxyacetophenones.
a 8 -1 8 -l 8 -1
Compound ¢corr kY,10 s k8,10 s kct'lo s
2-SMe 0.39 7.5 1.9 14.9
2-SBu 0.57 15.3 2.49 13.5
2-StBu 0.08 --- 1.02 11.8
2-SOMe 0.88 --- 44.9 6.1
2-502Me 0.41 0.016 0.078 0.14

 

aQuantum yield of acetophenone corrected flar50% recombination
of the initially formed radicals.

 

41

Charge-Transfer Quenching

 

Previous work on aminoketones has indicated a competi-
'thx1betweenintersystem crossing, charge-transfer quenching,

and y-hydrogen abstraction. Since ki *- 10 sec for

so
87

phenyl ketones, interaction of the amine with the excited

carbonyl must be comparably rapid to be able to quench the
singlet. However, intersystem crossing yields for the
ketosulfides are found to be one, indicating a much slower
rate of interaction. Despite this, the general trends should
be the same--that is, as the sulfur moiety is moved closer

to the carbonyl, the amount of charge-transfer quenching
should increase. The amount of charge-transfer quenchingiJ1
the present case is assumed to be the only significant decay
process of the triplet, as expressed by the following

equation:

1.
-‘F_kY+kCt (8)

Thus, knowledge of 'l' and the quantum yield allows calculation

of kct’ The effect of competing B-cleavage on kCt has

already been discussed in the previous section. Examination

of Table 5 reveals fairly high kct values for 5-SBu and 6-SBu at

7 1 7

14.2-10 sec" and 10.2-10 sec'l, respectively. As previously

found in azidoketones,88 kct is found to decrease by a factor

<often when the chain length is increased by one. For

8 1

instance, kct 9063 from 0.28-10 sec- in G-azidovalero-

8 l

phenone to <0.02'10 sec- in e-azidohexanophenone. The fact

that kc. for 5-SBu and 6-SBu are nearly identical is

t

42

disturbing. However, the qu of 6-SBu--i.e., 36.6--is nearly
identical to that for nonanophenone,89 which is nearly
equivalent to 6-SBu in size. Therefore, the sulfur does not
seem to be influencing the lifetime, yet the quantum yields
cannot be maximized. It then seems likely that most of the
inefficiency in 6-SBu is due not to C-T quenching by sulfur
but to some other effect which prevents solvation of the
biradical. This effect has been observed previously for very
long-chain ketones90 and in this laboratory for long chain
ketones that contain a heteroatom.91 The kY that one would
expect on inductive grounds for 6-SBu is ~1083ec-1, which is
roughly a factor of ten less than 5-SBu.

Conformational Effects. The fact that overlap of

 

donor and acceptor orbitals is necessary for efficient
quenching was demonstrated by Wagner and Scheve92 with the
1-methyl-l-benzoylpiperidine system. Thus, one would expect
that intramolecular quenching in an acyclic system would
depend upon the mobility of donor and acceptor relative to
each other. The approach of the sulfur and carbonyl moieties
corresponds to the formation of different sized rings and
should compare qualitatively with the known propensities of
molecules 1x: form various sized rings in the ground state.
For example, the kct's for 5-SBu and 6-SBu are considerably
less than those of 4-SBu and 3-SBu. The former case corres-
ponds to 7- and 8-membered rings, whereas the latter, 6-

and 5-membered rings, respectively.

43

 

p u
(4-SBu) ' (6-SBu)
6-membered ring 8-membered ring
stable unstable

The formation of 5- and 6-membered rings--i.e., B- and y-
substituted phenylketones--represents the maximum amountcnf
quenching. A dramatic reversal of trend is noted in going
from 3-SBu to 2-SBu in that kct decreases markedly. This
must reflect the conformational instability of small rings
as well as large rings since approach of donor and acceptor

in 2-SBu would represent a 4-membered ring.

i: gbu
va/-‘\/

(2-SBu)
4-membered ring
unstable

In the case of the a-thioalkoxyacetophenones, B-cleavage
followed by rapid in-cage recombination leads to inefficiency
not ascribable to C-T quenching. Table 8 lists the corrected

kct's for the a-substituted acetophenones.

44

Although full electron transfer is not takingplace,93
the C-T complex is conformationally constrained, resembling
more a tight ion-pair. Wagner and Ersfeld94 have shown that
in benzene no proton transfer is taking place in 9 since

the acidic hydrogens a to the positive nitrogen are inacces-

sible to the oxygen anion.

 

However, in the case of the 0:—thioalkoxyacetOphenones, the
charge-transfer complex presents a more favorable situation for
proton transfer although formation of the complex itself may be

slow.

Padwa95 has shown that products do indeed arise from the C-T

*
state in .1_°_ since flpossesses a lowest 30,0 triplet which is

0‘
' h" ‘* __> «ii/'3
Ph’Ph/gvsvph —’ PWWSVPh . Ph’P ' W

l_0 /

TYPE 11 PRODUCTS (1) = 0.04

45

inert to hydrogen abstraction. Perhaps coincidentally, the
quantum yield Padwa observed was identical to the value
measured for 2rStBu in the presence of 0.05M thiol.T%erefore,
it is possible that products arise in Padwa's system via
B-cleavage followed by hydrogen abstraction from starting
material which possesses highly abstractable hydrogen atoms

as shown below.

9
10 h" > h/Ph/C\. + 'Svph

—‘ 7 P
/19
O

B-cleavage
n P.
PH ph’ -

Unfortunately, the available data ch) not allow further
speculation.

Product formation from the charge-transfer state in
the present system has not been rigorously investigated.

Effect of Donor on kct- In the case of phenylamines,
the nitrogen leads to increased electron densitijlthe ring
which, in turn, leads to a more favorable interaction between
excited species and the conjugated system, resulting in more
efficient quenching relative to aliphatic amines.96 However,
phenylsulfides are less efficient quenchers than aliphatic

97

sulfides, which indicates that quenching arises primarily

46

by interaction of the non-bonding electrons of sulfur.
Electron withdrawing groups on the sulfur, like phenyl,
decrease its effectiveness. Thus, 3-SPh quenches about

98 noted a difference of

four times slower than 3-SBu. Cohen
about nine between n-butylsulfide and phenylsulfide in the
bimolecular quenching of the photoreduction of benzophenone
by isoborneol with sulfides. That S-SAc and S-SCN quench
about seven times slower than 5-SBu is also indicative of

the effect electron withdrawing groups have on the avail-
ability of the non-bonding pairs on sulfur.

Expectedly, increasing the oxidation state of the
sulfur moiety leads to a decrease in the rate of charge-
transfer quenching. For instance, 4-SOBu quenches about
eight times more slowly than 4-SBu, and 4-SOZBu about 2500
times more slowly than 4-SBu. The reduced rates of
quenching for sulfoxides relative to sulfides is attributable
to the decreased availablity of the electrons on sulfoxides.
This, in turn, is manifested in a higher ionization potential

than sulfides.99

The nature of the C-T complex in sulfides
and sulfoxides is pictured below and can be represented as
interaction of the non-bonding electrons on sulfur with the

triplet.

, O
6 18R 5 C?- JLSR (DJ/(R Ufa
l
Pn/4%\c_/J Ph/€K\__/J f%y/¢ p ,

47

Sulfones, on the other hand, are completely oxidized and
possess no non-bonding electrons except for thosecn1oxygen;
and, as such, the previous representation seems inappropriate.

Sulfones can best be represented by a resonating decet

100
structure.
R O- R O_' R O
\ x“
ES<1 é—-————9 /}£;f e———___9 >34'
R \o R 0‘ R/\o‘

Formally, C-T quenching can arise by interaction with either
the lone pair of electrons on oxygen (lla) or with a n-bond

between the sulfur and oxygen (11b).

. \ IO ' O -
(I)- + S<R ('3 Vi)? U5;
ph/CQ Ph/C\_/' arah .

11a 11b

While these structures are aesthetically pleasing, they seem
intuitively wrong in light of the high ionization potentials
of sulfones.101 Other mechanisms leading to inefficiency are
possible. The polar nature of the sulfonyl group may lead

to some ground state complexation which could, in turn,
behave differently than uncomplexed ketone, leading to decay.
Internal solvation of the benzoyl group by the sulfonyl group
may actually be switching the triplet levels from lowest

3

* *
n," to a lowest 30,0 , which might lead to enhanced decay.

One final intriguing mechanistic possibility to explain why

 

48

sulfones quench is by invoking "sandwich" type exciplex
formation where the triplet carbonyl lowers the reduction
potential of the sulfone enough to allow C-T complexation

with the solvent, in this case benzene.

 

 

 

, O R ~ - O\S /R
R Q83 A 886 ...... Md
Hy/C\\__/J O I INY/C\\__/J
hv ?///£//3///’
K

Such a mechanism may explain why sulfones quench intramolec-

ularly but not intermolecularly, since such a mechanism

would necessarily require strict conformational alignment,

which would not be fast enough on a bimolecular level.
Direct energy transfer to sulfones is unlikely,

102

however, due to its highly endothermic nature.

Bimolecular Quenching. Cohen103 has previously

 

measured the bimolecular rate constant for quenching of

benzophenone photoreduction with isoborneol by sulfides and

found it to be 6.6'108M-lsec_1. Cohenl04 later quenched the

phosphorescence of benzophenone with various alkyl and aryl

sulfides. The kq for butylsulfide in benzene was measured

at 8.3'108M-lsec-l. This is in fairly good agreement with

the present value of 3.25-108M-lsec-1. Comparing this with

the intramolecular kCt for 5-SBu (1.42'1083ec"l

that having the sulfur at the 6-position correspondsrcmghly

), one finds

to that found in the intermolecular case.

49

The apparent lack of correlation between the intra-
and intermolecular rate constant for quenching by butyl-
sulfoxide and butylsulfone is disturbing. That is, butyl-
sulfoxide quenches 100 times more slowly intermolecularly
than intramolecularly, while butylsulfone does not quench at
all bimolecularly but quenches intramolecularly with a
rate constant of about 107sec-l. The explanation may lie in
the fact that the orientation needed for approach of the
sulfoxide or sulfone to the carbonyl is not known exactly.
Therefore, the proper orientation for quenching may only be
obtained fast enough intramolecularly. There are numerous
examplesloswhere intramolecular processes are immensely
favored in rate over intermolecular processes, and the dif-
ference does indeed seem linked to the fact that effective

concentrations of intramolecular processes are far greater

than those normally achievable.

Indications for Further Research

 

Synthetic Utility. One of the questions most often

 

asked of chemists is whether their research is good for
anything. In this case the answer is a definitive yes. The
synthetic utility of the Type II Reaction has been explored
only sparingly. It offers an excellent way to prepare
unusual olefins as well as substituted cyclobutanols. For
instance, the Type II Reaction has been used to synthesize

adamantene,106 a molecule which has eluded synthesis by

 

50

108observations

conventional methods. Lewis'le7and others'
that a-substitution increases cyclization products relative
to cleavage products have been ignored synthetically.

Products from C-T State. It is not clear in the

 

present study whether products can arise from the C-T state.

The compound below might give a definitive answer.

 

*
Since napthyl ketones have lowest 0,0 triplets,109 formation

of products here would be indicative of a C-T, proton trans-
fer mechanism like that proposed by Wagner.l1’0

Effect of Ring Substituents. The amount of charge-

 

transfer is dependent upon the ionization potential of the
donor. It should, therefore, also be dependent on the reduction
potential of the acceptor, in this case the benzoyl moiety.
Thus, electron donors or acceptors should raise or lower

the reduction potential, respectively, resulting in decreased
or increased rates of C-T quenching. The following system

would be representative.

SR

X X=CF3. CN, O’Me2. etc.

Nature of Quenching by the Sulfonyl Group. The idea

of a "sandwich" type exciplex is intriguing and could probably

51

best be tested by varying the ionization potential of the
benzene by using substituted benzenes. For instance,
anisole should cause a slight increase in the rate of
quenching since it donates an electron more easily. Perhaps
coupling products resulting from proton transfer to the

sulfonyl group from alkyl benzenes could be observed as

shown below.

\~/ 9
Om""""'-«~--.S{"“‘m~u... 9 . .
Ph/H\_/’ 0” O ——’ "—9 Ph\/\Ph

Energy Transfer Resulting in Homolytic Cleavage. Intra-

molecular energy transfer could be studied by the following

system:

ph/IOLM 9.1211, ph/fi\/\/S

:9///? ‘
RSH h/fi\¢/\\
PRODUCTS €—-———' P °+--SNamh

where energy transfer to the napthyl group could possibly

  

promote B-cleavage resulting in radicals which could be
trapped with thiols and measured. The effectcxfchain-length

could then be investigated.

PART II

RADICAL B-CLEAVAGE VIA EXCITED STATES
AND PHOTOGENERATED DIRADICALS

Phenacylsulfides

 

Results

Synthesis and Identification of Photoproducts

Various substituted phenacylsulfides were prepared
by reaction of the phenacylhalide with sodium thiophenoxide
in ethanol. The compounds and their respective abbreviations
are listed in Tables 9 and 10. For example, a-thiophenoxyace-
tophenone is referred to as 2-SPh and p-chloro-a-thiophenoxy-
acetophenone as Cl-ZSPh. In all cases the corresponding
acetophenones were observed upon irradiation in benzene. In
the case of 2-SPh, acetophenone was actually isolated by
preparative vpc. For t-ZSPh, isobutyrophenone was identified
by nmr. The other acetophenones were identified by compari-
son of vpc retention times with authentic samples. Thiophenol
and diphenyldisulphide were observed in most cases but not
measured. In the cases of s-ZSPh and t-ZSPh the corresponding
disproportionation products--i.e., acrylophenoneanuia-methyl-
acrylophenone--were not separable from propiophenone and
isobutyrophenone. However, a-methylacrylophenone was identi-

fied by observation of a singlet at about 1.65 in the nmr.

52

 

53

The other radical coupling products--i.e., the 1,2-dibenzoy1-
ethanes--were not observed under the analysis conditions but

111

have been identified and measured previously. Surprisingly,

no benzaldehyde formation was detected in PDS.

Quantum Yields

 

The quantum yields for the appropriate acetophenone
formation were measured in benzene at 313019. in the same manner
as that described in Part I. The addition of benzenethiol
was found to maximize the quantum yield as shown in Figure 5.
Enhancements of quantum yields were typically on the order
of two to five. Nearly 100% material balances were observed
in the cases measured. The quantum yields are presented in

Tables 9 and 10.

Quenching Studies

 

Stern-Volmer plots for the quenching of acetophenone
were performed at 3660A as previously described with either
napthalene or l-methylnapthalene as quenchers. The use of
1,3-pentadiene gave irreproducible results probably because
of radical scavenging. The photoreactivity of certain com-
pounds was found to be unquenchable even with 2.0M naptha-
lene; thus, no information regarding the triplet was avail-
able. The corresponding kinetic parameters are listed in
Tables 9 and 10, and a representative Stern-Volmer plot is

shown in Figure 6.

54

Intersystem Crossing Yields

 

The intersystem crossing yields were not measurable
for the phenacylsulfides. Attempted sensitization of cis-
l,3-pentadiene resulted in meaningless numbers, probably
because of the production of radicals which isomerized the
olefin. Use of trans-stilbene as the sensitizee with
OMe-ZSPh resulted in an intersystem crossing yield in excess
of 3. The intersystem crossing yield must be at least 50%
for the quenchable compounds since the reactions were

totally quenchable.

Spectroscopic Studies

 

The uv spectra of selected substituted phenacylsul-
*
fides were measured in heptane, and the Amax for n,n and

n,0* transitions and e's are listed in Table 11.
Interestingly, vibrational fine structure on the n,n*
shoulder was observed in all cases. Substitution of ethanol
as solvent eliminated the fine structure. Representative
spectra indicating the solvent effect are presented in
Figure 7.

Corrected phosphorescence spectra (see Experimental

4M ketone

Section) were obtained at 77K at approximately 10-
in methyltetrahydrofuran (MTHF) glasses. The triplet
energies are presented in Table 12 and the actual spectrajxl

Figures 8 through 12.

55

Table 9. Quantum Yields and Rate Data for p-Substituted

 

 

 

Phenacylsulfides.
Compound 0a ¢maxb'c qu
9.
\v/SPh
H!”
H (2-SPh) 0.08 0.24 e 0.02 ---°
- 0.26 : 0.03d

F (F-ZSPh) 0.05 0.24 ---C
c1 (Cl-ZSPh) 0.05 0.24 0.80
Br (Br-ZSPh) 0.02 0.20 2.00 t 0.10
Me (Me-ZSPh) . 0.05 0.30 ---°
OMe (OMe-ZSPh) 0.09 0.41 1 0.03 2.20
SMe (SMe-ZSPh) 0.04 0.19 30.0 t 2.0
NMe2 (NMez-ZSPh) 0.07 0.19 13.8 i 0.8
4 (0-ZSPh) 0.05 0.27 40.0
CN (CN-ZSPh) 0.04 0.16 r 0.01 1.08 e 0.2

 

aAll 0's were obtained in benzene at 31303.
bMaximum yields were performed in the presence of 0.05M 05H.

cUnquenchable with 2.0M napthalene or 1-methylnapthalene.

d
¢-K

eThese are the observed quantum yields. Table 14 lists the
quantum yields corrected for about 50% in—cage recombination.

56

 

 

 

oa.o e om.m meo.o e eo.o In- Asmumumv
new
on-.. 3.0 2.0 3.82-3
oo.o H mm.H «6.0 eH.o lemmmnsoc
6mm.o semWV/,
0... No.0 0 em.e mm.e ieemmuuv :
cam.o
04-- Ho.e H mm.o o~.o Anemmumv
pvx mee e pcsomfioo
n m
.mmvflmanmawoNcmmlu ucmwum> haamusuoauum How sumo mumm can mvamww Esusmso .OH OHQMB

57

.Uonsmmme DOZM

.ea magma :e 0000efl 000 00H0es 2500000 0000000060

.mu
60

.manmzocmsqcso

mms Zmo on

.Momam um mcmucmn ch

 

 

5mm

I vao.o woo.o Amomv sm\L//

__

0

cm
- See -..- 30003 Jaw
me

e n 9 _Me vasomfioo

 

 

1.0.ucoo. .oa 0Hnme

58

'k *
Table 11. Substituent Effects on n,n and 0,0 Transitions

in Phenacylsulfides.a

 

 

 

* *

Compound xmax(n’" ), nm Amax("," ),nm

3 340 (372) 240 (8,157)}3

say/C‘\/’SB“ 336 (634)b 242 (10,382)
8

/K::ZTA3\V/Sph

X e

H 341 (448) 246 (19,462)

CN 355 (809) 248 (31,181)

OMe 336 (649) 257 (19,603)

SMe 340C 307 (20,183)

NMe2 330c 325 (27,067)

 

aIn heptane; molar extinction coefficients in parentheses.

*
bIn ethanol; fine structure on n,n band has disappeared.

* *
C:10,“ buried under «,1: ; estimated by comparison of fine struc-

ture with other compounds.

59

Table 12. Triplet Energies of Ring-Substituted Phenacyl-

 

 

 

sulfides.a
Compound Et(kcal)
H 70.9 (74)
C Bu
SPh
X x
H 73.5 (74)
CN 68.4 (69.2)b
OMe 70.4 (71)
NMe2 62.6

 

aNumbers in parentheses refer to the corresponding ring-
substituted valerophenone in 2-methylpentane. (Seeref.112)

bE. J. Siebert, unpublished.

60

 

 

 

 

 

 

0.3 ~
0 j
4
0.2 0
0.1 -
S i
i I fij r I
0.1 0.2 0.3 0.8
[48H]

Figure 5. Quantum Yield of Acetophenone Formation in 2-SPh
Versus [05H].

 

61

 

 

6.4
5‘
4-1
2° .
¢ A
3'1
0.5 1.0 1.5 2.0
[napthalene],M
Figure 6. Stern-Volmer Quenching Plot for the Quenching of

the p-Substituted Acetophenone Formation from
Cl-ZSPh (O), Br-ZSPh (Q), Me-ZSPh (A), and
CN-28Ph.(‘k) with Napthalene in Benzene.

62

.10:0060:120Hooo.o u a .Amoumvzmmaoco.o n o
.Amcmummnvzeaoo.o n m .Amoumvzmmaoo.o n ma .smmlm mo mnuommm umaoa>muuaa .5 musmflm

Ezomv cow omm mNm oom mhm omm com

 

 

 

 

 

 

63

 

 

 

 

 

 

350 400 450 500 550nm

Figure 8. Phosphorescence Spectrum of 2-SBu in MTHF at 77K.

64

 

 

 

 

350 400 450 500 550nm

‘ Figure 9. Phosphorescence Spectrum of 2-SPh in MTHF at 77K.

65

 

 

 

 

 

350 400 450 500 550nm

Figure 10. Phosphorescence Spectrum of OMe-ZSPh in MTHF at
77K.

 

66

 

 

 

350 400 450 500 550nm

Figure 11. Phosphorescence Spectrum of NMe -28Ph in MTHF at

77K. 2

 

67

 

 

 

 

370 420 470 520 570nm

Figure 12. Phosphorescence Spectrum of CN-ZSPh in MTHF at
77K.

68

Discussion

Mechanism

 

The free radical nature of photoinduced B-cleavage
of B-ketosulfides has been firmly established by careful
examination of product distributions.113 On the other hand,
certain substituents display a propensity toward heterolytic
cleavage as in the case of a-tosylketones, which result in
rearranged products typical of carbonium ion chemistry.114
In the present system, the detection of coupling products--
namely, diphenyldisulfide--and the fact that thiols, which
are known radical scavengers, greatly enhanced the quantum
yields, eliminated heterolytic cleavage as a mechanistic

possibility. The mechanism of photoinduced B-cleavage of

B-ketosulfides is presented in Scheme 5.

diffusion out
ofcmge

RSH
O

coupfing (sh/[L~

products

 

Scheme 5. Mechanism of B-Cleavage of B-Ketosulfides.

69

As in free radical systems,115 fairly strict stereo-
chemical alignments between the radical center and the bond
that is breaking would be expected. Thus, two important
conformations need to be considered: conformation 13! in
which the bond that is breaking is parallel to the benzoyl
fl-system, and conformation 13, in which the breaking bond is
parallel to the C-0 bond and the sulfur and oxygen are
eclipsed. Previous studies on carbonyl compounds116
containing a-heteroatoms have indicated that conformations
12 and 13 are present in about equal amounts in solution.

In fact, d—haloaldehydes and ketones exist primarily in
conformation _]._3_ where the carbonyl and halogen atom are nearly
eclipsed. However, in the case of a-thioalkoxyaldehydes117

conformation 12 is clearly dominant. The analogous thio-

alkoxyketones have not been studied. On the other hand, IR

   

J:

 

studies have shown a-bromocyclohexanone exists primarily
in the conformation where the bromine is axial, while the
a-chlorocyclohexanone exists in the conformation where it is
equatorial. The situation is obviously fairly complicated;
however, other factors aside, conformation 12 clearly
represents the sterically favored orientation. In fact,

such a conformation seems rigidly required by analogy with

70

119 120
the a-tosyloxy- and a-aminocyclohexanones which cleave

only when axial. Further support for conformational control
of B-cleavage can be gleaned from the fact that phenyldesyl-
sulfide (PDS) reacts with a quantum efficiency far below

the other phenacylsulfides. Examination of the three impor-
tant conformational possibilities reveals a possible reason

for this.

SPh

 

16

I“
.b

In this case, alignment of the proper orbitals as in 14 and
15 causes serious eclipsing interaction between the two
phenyl rings or the carbonyl and phenyl ring. Therefore,
the amount of conformation 16 present at any time will be
higher than normal; and as such, the amount of C—T quenching
will be increased.

Consideration of conformation E does not suggest
straightforward type of elimination. However,the geometry
enables maximum overlap of the n-orbital on oxygen and one of the
lone pairs on sulfur. This conformation allows C-T complexa-
tion as discussed in Part I and product formation from such
a complex must be considered. One possible mode of cleavage

can be envisioned as follows:

71

 

However, this seems unlikely in light of the fact that an
analogous mechanism is also possible for equatorial
a-tosyloxy- and a-aminocyclohexanones, which do not react.
Also, 2-SOtBu cleaves smoothly in spite of the fact that

SOtBu would be a poor anionic leaving group.121

O

n/\- + -SO+

Pmiy; + ’80—}—

Another mechanistic possibility exists. Direct
energy transfer from the carbonyl to the sulfur moiety could

result in homolytic cleavage as shown below.

b

I '0' ‘ ?
Ph/k/sph ——+ Ph/VSPh ——> PRODUCTS

The preferred orientation necessary for energy transfer in
this case is unclear. Charge-transfer complexation, on the

other hand, between the n-orbital and the lone electron pair

72

on sulfur can occur only from conformation 13. Triplet-
triplet energy transfer for 2-SPh would be slightly endo-
thermic since the triplet energy of thioanisole is

~76 1:001.122

As substitution on the benzoyl moiety lowers
the triplet energy, the exchange would become even more
endothermic. In any event, products from homolytic cleavage
in 3-SPh and 4-SPh were not observed; so it seems that
product formation via energy transfer is unlikely.
Therefore, conformation 13 results mainly in C-T

quenching of the excited carbonyl. The amount of this

quenching will be discussed later.

Quantum Yields

 

Tables 9 and 10 present the quantum yields for a
variety of structurally variant phenacylsulfides. The addi-
tion of benzenethiol leads to fairly large quantum yield
enhancements. Out-of—cage coupling is a fairly efficient

process, usually leading to respectable yields of dibenzoyl-

123

ethane. Near quantitative material balances in the

presence of thiols indicate that all the radicals are
scavenged before they get a chance to couple. The rate

constant for trapping by alkylthiols (kt) is<31the order of

107M-lsec-l.124 The rate constant for trapping by PhSH.can

be estimated from the addition of thiols to Vinylcyclopro—

pane125 as shown in Scheme 6. When benzenethiol is used,

100% of product E is formed, which indicates that kt > kc. If

kcnv107sec-l,126 kt for PhSH must bel~108M-lsec-l.

 

 

RSH %_1_7 %_8_ Rs?-
CH SH 12 88 \A

08H 100 0 lg

 

Scheme 6. Addition of Thiols to Vinylcyclopropane.

Examination of Table 10 reveals some interesting
information regarding s-ZSPh and t-ZSPh. Although the dis-
proportionation products--i.e., vinylacetophenone and
a-methylacrylophenone--could not be separated from their
saturated analogues under the analytical conditions, nmr
experiments on t-ZSPh allowed approximate measurement of
the amount of a—methylacrylophenone (MAP). Curiously, no
enhancement of quantum yield was observed for either compound
upon the addition of PhSH. Table 13 lists the approximate
amounts of reduction and disproportionation products from
t-SPh as estimated by nmr experiments. In the presence of
thiol, it is assumed that most of the radicals that diffuse
out of the cage are trapped. Thus, most of the dispropor-
tionation product (MAP) in the presence of thiol is probably

coming from in-cage disproportionation. The slight

74

Table 13. Approximate Percentage of IBP and MAP Found:h1the
Photolysis of t-ZSPh.

 

 

fl
Solvent Phj\< PM ¢IPB + MAP

 

(IBP) (MAP)
Benzene 45 55 0.33
Benzene 83 17 0.34

0.05M 05H

 

predominance of MAP in the absence of thiol is also indica-
tive of in-cage disproportionation. The amountscflfIBP and
MAP are comparable in the absence of benzenethiol,indicating
that out-of—cage disproportionation greatly predominates
over coupling as is the case for t—butyl radicals.127 Data
arexufi:availab1e for s-ZSPh, but one would expect a lesser
predominance of disproportionation over recombination due to

the diminished amount of B-hydrogens.128

Spectroscopy

 

Any discussion of substituent effects upon the rate<xf
a photoreaction must include an examination of the nature of
the excited state or states responsible. Since the 3n,fi*
and 30,0* states are in energetic proximity for phenylalkyl
ketones129 and the benzene 0,1r* excitation energy is strongly

influenced by substituents, the effects of substituents upon

* *
the energy levels of the n,“ and 0,0 triplets must be noted.

75

*
Both electron donors and acceptors stabilize 0,0

130

transitions, with the exception of the strongly with-

drawing CF3 group, which tends to increase the S°+1LA transi-
tion energy since it cannot extend conjugation.131 Thus,
the conjugative effects generally outweigh any inductive
effects. While electron donors stabilize the S,,->]'LA transition
of acylbenzenes,they tend to destabilize n,0* transitions,
eventually resulting in inversion of the triplet levels for
strong donors.132 The effect of substituents upon the

* *
ordering of n,0 and 0,0 states is presented below.

 

 

 

0,0
*
n,0
\ *
0,0

*
nzn CH3
CF3 OCH3
H SCH3

Table 12 presents the triplet energies of some ring-
substituted phenacylsulfides. The phosphorescence spectrum
of 2-SBu is presented in Figure 8 and strongly resembles valero-

phenone in which the vibrational structure corresponds to

the ground state carbonyl stretch.133

The triplet

energy is about 3 kcal lower than valerophenone due to the
inductive effect of the a-thioalkoxy group, which stablizes
the n,0* state slightly. The spectra of the a-thiophenyl-

acetophenones (Figures 9 through 12), on the other hand,

*
show a marked lack of structure, resembling more 0,0 states.

 

76

Disturbingly, the E for the a—thiophenylacetophenones are

t
almost identical to the corresponding ring-substituted
valerophenones. The discrepancy here is why does SBu

lower the Et energy relative to the corresponding valero-
phenone but SPh seems to have no effect. Several possibili-
ties seem to exist. One possibility is that emission is
being observed from two different n,0* triplets, analogous
to that observed in the dual phosphorescence of phenylalkyl-

ketones.134

Thus, two excited state conformations, the
higher in energy of which resembles the ground state con-
formation, would yield different Et's. Extrapolation to the
phenacylsulfide case presents the possibility that 70.9 kcal
represents the conformationally relaxed emission of 2-SBu,
whereas the values for the a—thiophenylacetophenones repre-
sent emission from a higher, unrelaxed state. Therefore,
the increase in energy would offset the decrease expected on
inductive grounds. The difference between SBu and SPh apart
from extended conjugation in SPh are primarily steric in
nature. Since dual phosphorescence is highly dependent upon
the nature of the solvent,135 which in turn determines the
orientation of the carbonyl and sulfur groups in the glassy
matrix, subtle changes in conformational orientation could
result.

A more obvious possibility is that 2-SPh is actually
a lowest 0,0* state (p-OMe and p-NMe2 are most certainly so),

*
whereas 2-SBu is n,0 in nature. The inductive effect of

*
the a-substituent would not be expected to affect a 0,0

at
state as much as an n,0 state.

77

Lastly, a disturbing possibility is that B—cleavage
to yield a radical pair is competitive with emission in the
glassy matrix. If that is the case, the emission would
actually be from the acetophenone moiety, and the lack of
structure in the phosphorescence spectra could be explained
by its free radical nature.

The effect of a-substituents on the uv spectra is
also interesting. The intensification of the n,0* transi-
tion and its subsequent red shift relative to the unsubsti-
tuted ketone has been noted previously for a-heteroketone
spectra.136 In fact, the original observation by Jones137
has since been extensively used in conformational analysis.
Again, two conformations need to be considered: one, where
the C-X bond is parallel to the 0-system which corresponds
to an axial substituent for a cyclohexanone as in conforma-
tion 12, and two, where the C-X bond is parallel to the C-0
bond corresponding roughly to the analogous equatorial
cyclohexanone substitutent as in conformation 13.

The intensification of the n,0* absorption and its
shift to longer wavelength is observed only for axial sub-
stituents. Equatorial substituents on a-substituted cyclo-
hexanones produce either no effect or cause a slight blue
shift. Allinger138 has ascribed this effect to hyperconju—
gation between the C-X bond and the carbonyl 0-system.
Interaction between the carbonyl 0* level and a low lying
C-Xo* orbital when X is axial gives rise to a red shift.

Hoffmann139 has recently treated the a-aminoketones

78

theoretically and found Allinger's arguments essentially
correct in that the hyperconjugation effect is extremely
dependent upon C-N/0-system alignment. Little beyond thisis
known about the (as-heteroatom effect, but the nature of the

140

effect can perhaps be likened to the Murrel or Labhart-

141 models for B-Y unsaturated carbonyls. In any

Wagnier
event, it seems that enhanced absorptions are observed when-
ever a carbonyl and group of low ionization potential are
present with proper mutual geometric disposition.

Table 11 presents the uv data for selected substi-
tuted phenacylsulfides, and Figure 7 shows the actual spectra
of 2-SBu in heptane and in ethanol. As mentioned previously,
fine structure is observed in the nnr* shoulder for all
compounds in heptane but disappear when ethanol is used as
solvent. This observation is a rare occurrencelnn:has been
observed previously in cyclobutanone142 and exo-dicyclopenta-

143

dienone. Interestingly, the spacing of the structure

corresponds to the stretching frequency of the excited
carbonyl singlet (about 1200 cm-l).144

Differing behavior between a-SBu and a-SPh substi-
tuents are also noted in the uv. SBu stabilizes the n,v*
transition relative to acetophenone (Amaxn,fl* = 316nm) but
does nothing to the 0,0* transition. However, SPh stabilizes
both n,0* and 0,0* transitions. There is obviously some
interaction between the phenyl ring and the benzoyl fl-system
but the exact nature of this observation is unknown. As

145

noted previously, electron donating groups tend to

'k *
stabilize the 0," transition while raising the n,0

 

79

*
transition energy. Conversely, CN-ZSPh stabilizes the n,0
*
transition but also lowers the 0,0 band because of its

ability to extend the conjugation.

Rates of B-Cleavage and Charge-Transfer

The rate constant of B-cleavage, k is calculated

8!
from equation 9.

_ corr (9)

where ¢co equals the observed quantum yield multiplied by

rr
two to correct for about 50% in-cage recombination. The
remaining inefficiency is assumed to be due to C-T quenching
and is calculated as mentioned previously from equation 8.
The rate data are listed in Table 14.

The rate of B-cleavage can be influenced by three
factors: the nature of the excited state, the stability of
the incipient radicals, and the overall thermodynamics of
the system.

A consideration of the effect of excited state upon
reactivity centers upon the dichotomy between the n,0* and
0,0* states. As can be seen from the phosphorescence
studies, all substituents tend to lower the triplet energy.
However, the lowering of the triplet energy is accompanied
by an opposing effect. That is, electron donors are

indeed lowering the Et' but they are also inverting the

* *
ordering of the n,0 and 0,0 states. Incomplete knowledge

80

 

 

 

Table 14. Calculated Rate Data for Various Phenacylsulfides.
Compound 0;:ira 31131085.l k8,1083-l ct.1083
2-SPh 0.48 --- >100 ---
F-ZSPh 0.48 --- >100 ---
Cl-ZSPh 0.48 62.4 30.0 32.5
Br-ZSPh 0.40 25.0 10.0 15.0
Me-ZSPh 0.60 --- >100 ---
OMe-ZSPh 0.82 22.7 18.4 4.30
SMe-ZSPh 0.38 1.67 0.63 1.04
NMez-ZSPh 0.38 3.62 1.38 2.24
0-23Ph 0.54 1.25 0.68 0.58
CN-ZSPh 0.32 46.3 14.8 31.5
s-ZSPh 0.64 -—- >100 ---
t-ZSPh 0.68 --- >100 ---
cy-ZSPh 0.84 36.2 30.4 5.80
4'-MSPh 0.80 --- >100 ---
2-StBu 0.08 12.8 1.02 11.8
4'-SPh <0.002 --- --- -—-
PDS 0.02 --- --- ---

 

aCalculated by doubling

the observed quantum yield.

81

of the multiplicity of the reaction prevents a good corre-
1ation between the phosphorescence and uv data and the
observed reactivity. However, all reactivity comes from the
triplet state in the compounds which are quenchable--it is
the efficienty of triplet formation which is unknown. One
general observation is applicable--i.e., electron donors
tend to slow down the reaction. However, this immedicately
implies that 0,0* states are less reactive than n,0* states.
The reduced hydrogen abstraction ability of the carbonyl in
the 30,0* state is understandable in terms of its greatly
reduced electrophilicity,146 but the mechanism of B-cleavage
requires only that there be free spin on the carbonyl carbon.

The valence bond representation of the respective

states are shown below.

57’ .11.

n,0

We

*
The main difference between the two is that in the n,0

 

 

state, an electron from the n-orbital on oxygen is promoted
to a 0*-orbital, whereas the 0,0* state results from promo-
tion of an electron from the 0-system to a 0*-orbital. Both
representations, however, indicate significant amounts of
spin on the carbonyl carbon, but in actuality it is known

*
that most of the excitation in 0,0 states is localized in

82

the benzene ring.147 Thus, it would appear that the observed

decrease in rate with electron donating substituents is due
to 21 decreased amount of spin density at the carbonyl
carbon. In simpler terms, the n,0* state resembles a 1,2-
biradical, whereas a 0,0* does not.

Table 14 reveals a difference in the observed rate

of C-T quenching, k between the electron donating and

ct’
releasing substituents. Charge-transfer occurs primarily
between the lone electron in the n-orbital and the lone pair
on sulfur in the n,fl* state. Not much C-T formation between
the 0-system in the 0,0* state and sulfur is expected since
the oxygen is already "electron rich." Thus, as the lowest
triplet becomes 0,0*, a decrease in kct is observed. Any<>4P
involving the 0-system would in any event be decreased by
electron donating groups. The effect of a p-CN-substituent
is curious. It has the effect of decreasing the rate of
cleavage much like electron donors; and, in fact, its phos-
phorescence spectrum resembles a 0,0* state. However, its
strong electron withdrawing effect increases the amount of
kct by lowering the reduction potential of the carbonyl.
As mentioned in the Introduction, the interposition of a
0,0* state for a n,0* state has been shown to eliminate (or
greatly slow down) B-cleavage.148

As is the case in free radical chemistry, the sta-
bility of the incipient radicals in part determines their rates

149

of formation. The kB for cy-ZSPh is less than t-ZSPh.

The difference here presumably lies in the difference in

 

83

a tertiary radical and a 3° cyclopropyl radical. The
instability of the cyclopropyl radical probably reflects its
inability to attain a planar sp2 configuration.150 The
cyclopropyl radical is surpassed only by the phenyl radical
in difficulty of formation.151
The nature of the leaving group--i.e., the sulfur
moiety--probably has the greatest effect on the rate of

B-cleavage. Table 15 lists some relative rates<xfB-cleavage

for various phenacylsulfur moieties.

Table 15. Relative Rates of B-Cleavage in Phenacylsulfides.

 

 

8 l

 

Compound kB,lO sec krel
Z-StBu 1.02 l
Z-SOMe 44.9° 44
2—SPh >100 >196

 

aData from Table 8.

That -SPh is more stable than SR has been demonstrated

152

repeatedly. The order of stabilities--i.e. , SPh > SOR >

SR > SOzR--confirms Rice‘s153 original suggestion that SOR

has the greatest kinetic stability compared to SR or SO R.

2
A more detailed discussion of leaving groups will be forth-

coming in the section on G-substituted valerophenones.

84

The strength of the C-S bond in the phenacylsulfides
is intrinsically related to the stability of the incipient
radicals. The bond dissociation energy for CH3SPh+ ~CH3 +

154 and would probably be lower

~SPh equals about 60 kcal/mole
for 2-SPh since an d-keto radical is being formed rather than
a methyl radical. Thus, even in the case of NMez-ZSPh, where
the triplet energy is about 62 kcal/mole, the energy requirements
are sufficiently met. However, as the triplet energies are
lowered, the gap between the bond dissociation energy and
the triplet energy becomes smaller, or less exothermic, and
may explain the observed decrease in rate of B-cleavage. The
bond dissociation energy for CH3SCH3 + ~CH3 + ~SCH3, which
would correspond roughly to B-cleavage in 2-SMe, is about

73 kcal/mole.

Indications for Further Research
Estimation of In-Cage Coupling. A more accurate esti-
mates for the amount of in-cage radical recombination could

be gained by studying the following compounds:

l+

Generation of the two radicals might be possiblekurextrusion

of SO2 from the thiosulfonate, thus yielding the desired

85

radical pair. There is, however, the question astx>whether
this would be an in-cage process.

A measurement of the extent of racemization of an
optically active phenacylsulfide might give some indication
of the amount of in-cage recombination.

Generation of Free Radicals. This system offers an

 

excellent way to generate free radicals. Processes such as

intramolecular or intermolecular additions could be studied.

0
II

o O
I SR H . 'SR
hv etc.
—> O? -—> CO —»
¢ //

This system also offers an excellent opportunity to
study solvent effects upon radical reactions since little

is known in this respect.

6-Substituted Phenyl Ketones

Results

Synthesis

 

The 6-substituted valerophenones listed in Table 16
were prepared by Sn2 displacement of d-chlorovalerophenone
with the sodium salt of the appropriate nucleophile. To
eliminate direct interaction between the benzoyl group and
G-substituent as the cause of elimination of HX, compoundstI
which the benzoyl group and X were inaccessible to each other

‘were synthesized as outlined in Scheme 7.

86

 

0 Nb
\L__ Benzene 2
1 \/co Me >
// § // 2 AICI3 Q
1)KOH
1 2)PhLi
O O

X =CL. «flNWBC)

. he ”X 0 h
X :8 BDMBC ‘
r ( ) Acetic acid

 

Scheme 7. Synthesis of 4-Halo-1,4-Dimethyl-l-Benzoylcyclo-
hexanes.

The Diels-Alder Reaction between isoprene and a-methyl-
methacrylate proceeded smoothly in benzene in the presence
of a catalytic amount of aluminum chloride. Interestingly,
a high degree of regioselectivity is observed in that only
the 4-methyl isomer is isolated. The directing effect of
AlCl3 and other Lewis acids is fortunate because the thermal
reaction yields significant amounts of the 3-methyl isomer.
Unfortunately, the analogous cycloaddition utilizing
oi-methylacrylophenone and isoprene did not go. It was feared
that thermolysis would lead to a inseparable mixture, so
this path was not pursued further. Subsequent hydrolysis of
the ester to yield the acid and reaction with two equiva-
lents of PhLi to form the phenyl ketone proceeded in 95% and

60% yields, respectively. Addition of HX was found to be

 

87

exceedingly sluggish in ether or hydrocarbon solvent but

was found to proceed smoothly in glacial acetic acid. In

the case of the bromo-derivative, the two diastereomers were
separable by fractional crystallization, but such was not the
case for the Cl isomer for which only one diastereomer was

obtained.

Identification of Diastereomers
Spectral comparison of the two bromide diastereomers
revealed significant differencesiJithe chemical shift in the

1H and 13

C for the l-methyl group. Based on experimental

free energy differences between axial and equatorial substi-
5 . .

tuents,ls the folloWing assumptions about the conforma-

tional equilibria were made:

o\\ “
O
<—— 3 ll
-’ Ph
r
C§§ “ r
.____9 O
h

Differentiation between the l- and 4-methyl groupsirs

156

straightforward. The effective shielding constant of

Br is larger than COPh, so one would expect the 4-methyl

group to appear farther downfield. A difference between

13

axial and equatorial absorption in the nmr and C have been

 

88

noted previously, where axial protons and methyl groups
usually resonate at higher field strengths.157 The conforma-
tional assumptions reveal that the l-methyl group is equa-
torial most of the time in trans-BDMBC, whereas it is mostly
axial for cis-BDMBC. Comparison with similar measurements on

18 and 12 by Lewis158 is revealing.

C
O\. CH3 61.28
h
Q
CH3 61.27
h
H3 61.43 g
r f
13

An analogous effect is noted in the C where the l-methyl
group in cis-BDMBC resonates at much higher field strength
than trans-BDMBC.

In the case of the chloride, the assignment was not
so straightforward since only one diastereomer was obtained.
However, by analogy with the bromo-derivatives, its physical
properties suggested it was the trans-isomer. An X-ray
structure (see Figure 13) confirmed the original suspicion.

Europium shift studies on the known trans—chloro isomer

and the suspected trans-bromo isomer related the structures and

89

confirmed the original assignments (see Figures 14, 15, and
16) . The photoreactivity of each diastereomer also supported

the assignments.

Identification of Photoproducts

 

All the G-substituted valerophenones produced aceto-
phenone and 4-benzoy1-1—butene (4-BB) in varying amounts.

In the case of 5-SPh, acetophenone and 4-BB were isolated by
preparative vpc and compared to authentic samples. Subse-
quent identification of acetophenone and 4-BB was made by
comparison of vpc retention times with authentic samples.

The radical coupling product from 5-SPh--i.e., diphenyl-
disulfide--was identified by comparative vpc retention

times. A small peak which was assumed to be the cyclobutanol
was observed in the vpc for S-SPh and certain other compounds.
The coupling product from 5-SOBu--i.e., BuSOZSBu--was identi-
fied by comparative vpc retention times. The olefinic
fragments resulting from Type II cleavage were not identified
or measured.

Elimination of p-methoxyphenol from 5-OPh was not
observed. Only acetophenone formation was observed. Cleav-
age of a C-O bond in 4-OBzhydl, resulting in the formation
of benzhydrol and B-benzoylpropionaldehyde was anticipated
but not observed. Again, only Type II cleavage was observed.

Unfortunately, BDMBC and CDMBC were found to be
extremely unstable to vpc analysis, yielding 1,4-dimethy1-1-

benxoylcyclohex-3-ene (DMBC) as a broad, tailing peak upon

90

injection on QF-l, SE-30 or Carbowax columns at various
column and injector temperatures. Analogous elimination of
HX was observed upon column chromatography on either neutral
alumina or silica gel. This decomposition greatly compli-
cated the identification of DMBC as a photoproduct.

However, prolonged photolysis of CDMBC resulted in
complete consumption of starting material and resulted in
two peaks in the vpc trace. The shorter retention time peak
was shown to be DMBC by comparison with an authentic sample,
whereas the longer retention time peak was assumed to be
the cyclization product resulting from y-hydrogen abstrac-

tion. Attempts to isolate this compound proved futile.

 

However, an IR of the crude photolysate revealed a fairly
1

intense OH absorption at about 3500 cm- . Addition of Br2
to the crude photolysate resulted in the precipitation of an
orange solid, which was found to be identical to the bromine
'addition product of DMBC. Furthermore, zinc dust debromina-
tion of the orange product yielded DMBC by vpc.

Lastly, the photolysis of trans-BDMBC in benzene-d6
containing 0.05M pyridine resulted in the appearance of

vinylic proton absorptions in the nmr. Since Type II cleav-

age products are not found to any significant extentixtthese

 

 

91

systems,159 the vinylic absorptions can be ascribed with a

fair degree of confidence to DMBC.

Quantum Yields

 

The quantum yields of acetophenone and 4-BB formation
from the 6-substituted valerophenones were measured as
previously described at 3130A and are presented in Table 16.
The solvent effects on II:4-BB ratios are presented in Table 17.

Since cis- and trans-BDMBC and trans-CDMBC decomposed
upon analysis, yielding DMBC, the product could not be
measured directly. Fortunately, trans-CDMBC was found to
decompose in consistent amounts to the extent of around 25%.
Enhancements beyond this value were taken to be equal to the
amount formed upon photolysis. However, cis-enuitrans-BCMBC
decomposed quantitatively, so quantum yields were determined
by measuring the disappearance of. pyridine, which complexed
HBr to form insoluble pyridinium hydrobromide. Benzaldehyde
quantum yields from cis- and trans-BDMBC and trans-CDMBC were
measured in the usual manner. The quantum yields for forma-
tion of DMBC and benzaldehyde from cis-anuitrans-BDMBC and

trans-CDMBC are listed in Table 18.

Quenching Studies

 

The Stern-Volmer quenching plots for the é-substituted
valerophenones were measured as previously described at
31303 with 1,3-pentadiene as quencher and have been listed
in Part I. The quenching plot for BDMBC and CDMBC were

measured at 36603 by quenching the disappearance of pyridine

92

with napthalene. The formation of benzaldehyde was quenched
by napthalene. These values are listed in Tables 18.

The effect of temperature upon k t for valerophenone
and 6-iodovalerophenone in benzene was determined. The plot

is presented in Figure 17.

 

93

Table 16. Quantum Yields of Acetophenone and 4-Benzoyl-1-

Butene Formation from Various 6-Substituted Valero-

phenones.

 

 

 

Compound ¢II ¢4-BB
H (S-X)
15th
x,
Cl 0.58a 0.10a
Br 0.05a 0.55a
I . <0.002a 0.43a
SCN 0.003 0.25
SAC 0.78 0.02
SBu - 0.21 0.006
SOBu 0.03 0.39
SOZBu 0.39 0.03
StBu 0.16 0.01
SOPh 0.003 0.32
SOZPh 0.19 0.22
SPh 0.015 0.28
0 -.—0Me ---b 0 . 00
ph//\\//\~/’ Ph Y

 

aMeasured by J. H. Sedon in the presence of 0.1M pyridine

(see reference 160).
b

No 4-BB detected. Acetophenone present butrxfi:measured.

c:No detectable B-benzoylpropionaldehyde. Acetophenone present

but not measured.

94

 

 

 

 

Table 17. Solvent Effects on B-Cleavage for Various 6-Chloro-
valerophenones.a
Compound Solvent ¢II ¢4-BB II/4-BB
fl Benzene 0.58 0.10 5.8
./\/\/\Cl Dioxane 0.36 0.06 6.0
CH3CN 0.54 0.08 6.8
MeOH 0.36 0.06 6.0
O Benzene 0.045 0.008 5.6
II
MeOH ---b ---b (22)
OMe
F Benzene 0.63 0.07 9.0
1 Dioxane 0.20 0.028 7.1
CF3 CH3CN 0.63 0.04 16
MeOH 0.43 0.03 14
aA11 measurements made in benzene containing 0.10M pyridine.

b
Too low to measure.

95

Table 18 . Quantum Yields and Rate Data for 4-Halo-l, 4-Dimethyl-
1-Benzoy1cyclohexanes.

 

 

Compound a k

 

 

c"c110 qTCHO ¢DMBC quDMBC
Ph
0.008 233 0.21 100
0.01b
c
O h
d
0.019 208 0.45(0.osm) 10.7
0.017 0.40(0.10md
Br
\Tf::::::;7LIr/Ph 0.11 210 0.12(0.051~4)d 65
B
Ph 0.20C 200 0.045 29

E

 

a0.02M 05H.
bPresumed to be bicyclic alcohol.

cSee reference 161.

dNumber in parenthesis refers to the concentration of added
pyridine.

96

ago.

.mmo_

\
/

-J/V ‘

/

.mU.

.Umzaoimcmuv mo musgosuum Hmummuo >mmix

_Go_ .mmoi

.eo.////

.moi

.HUH

-UH

_0_

.MH gunmen

97

 

 

 

 

 

 

 

 

 

 

 

 

 

 

r,
1
0\ Ph /
C1
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

5ppm

Figure .14 . NMR Spectra of trans-CDMBC in CDC13 (Bottom) ; in
CDCl3 Containing 0.0259g/0.5ml Eu(fod)3(Top).

98

 

 

 

 

 

 

 

 

 

 

 

8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0
GPPm

Figure 15 . NMR Spectra of trans-BDMBC in CHCl3 (Bottom) ; in
CDCl3 Containing 0.0259g/0.5ml Eu(fod)3(Top).

99

 

 

 

 

—————

 

 

 

 

f.
L @0011)

“J:
10.1.}

 

 

 

 

 

 

 

8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0
Gppm

Figure 16. NMR Spectra of cis-BDMBC in CDCl3 (Bottom) 7 in
CDCl3 Containing 0.02599/0.5ml Eu(fod)3(Top).

100

60“

40‘

 

 

 

 

10 20 30 40 50 60 70

Figure 17. Temperature Dependence of k r for Valerophenone
(A) and 6-Iodova1erophenone (A) in Benzene.

101

Discussion
Mechanism of Radical B-Cleavage via
Photogenerated Diradicals
The following transformation was first observed by
Wagner and Sedon.162 In light of the known propensities for

photoinduced biradicalsix>undergo rearrangements typical of

monoradicals, the mechanism seemed straightforward,

O O
I hv H HX
P -——-—>Ph/\/\¢+

x=CLBnI

proceeding by radical B-cleavage of the initially formed

1,4-biradical followed by disproportionation as shown below.

H H E?
MX—e Vii/V 'X _) PM? + HX

However, the rate of elimination of Cl deduced from such a
mechanism is much faster than that usually assumed.163 In-
asmuch as all biradicals possess some zwitterionic charac-
ter, anionic elimination as presented below seemed to be a

viable mechanistic possibility.

(DH (DH

HY%\~/Afirf\% ; pW/+\/”\//\y

 

102

Table 17 presents the quantum yields of ¢II and ¢4-BB for
various 6-chlorova1erophenones in different solvents. Little
variation in II:4-BB ratios are observed with solvent, except
in the case of p-methoxy-G-chlorovalerophenone in CH3CN and
MeOH. The ability of polar solvents to stabilize carbonium
ions is well known,164 and as such any zwitterionic character
of the 1,4-biradical should be stabilized in a polar solvent.
Therefore, if X is being eliminated ionically, stabilization
of the zwitterion form of the biradical should result in
greater amounts of B-elimination relative to Type EIcleavage.

Stabilization or destabilization of the zwitterionic form

can also be brought about by ring substitution.

   

X

Whereas, p-MeO should stabilize the carbonium ion, p-CF3
should destabilize it. In view of the 100 or 1000 fold
effect p-substitutents have upon ground state carbonium ion

formation,165

the fact that II:4-BB varies little with p-OMe
or CF3 in benzene is enlightening. On the other hand, p-CF3
substitution favors Type II elimination slightly in methanol
and CH3CN to the extent of a factor of about two. The
results for p-OMe-S-Cl in CH3CN and MeOH are confusing in
that just the opposite effect is observed. Here, in a situ-

ation where B-cleavage should be favored, Type II cleavage

predominates. However, the ability of polar solvents to

103

166 and the effect in

invert triplet levels is notorious,
the p-OMe-S-Cl case is to lower the quantum yields to such
an extent that accurate measurements are impossible. Thus,
the discrepancy could be due to analytical difficulties.
The extent to which p-substitution influences ks, the rate
constant of Type II cleavage, which is normally about
107sec-l,167 is unknown; however, it is safe to say that
solvent or substituent effects are at best extremely small,
and the ionic mode of elimination is probably only a small
contributor for only the worst radical leaving groups.
Formation of 4-BB or DMBC from their respective
precursors via either intramolecular or intermolecularinter-
action of the halide or thiyl groups with the excited benzoyl

group can be definitely ruled out. Irradiation of 4-SPh

resulted in no allylacetophenone formation.

0

hv O
Ph/H\/\/SPh +PH/|k/§ + HSPh

Interaction between the sulfur and the benzoyl groupsixtthis
case was shown in Part I to be faster than S-SPh and should
be even more favorable for photolytic elimination by the

above mechanism. Intermolecular interaction in the case of

BDMBC was ruled out by the following control experiment.

r hv

acetophenone \\ \
benzene V?

0.5M pyridine

 

104

This coupled with the fact that alkyl.halides<k3not quench
triplets168 eliminates any intermolecularly sensitized
elimination mechanism.

Another interesting mechanistic alternative, analo-

gous to that already suggested for B-alkoxyketones, is a

cyclic concerted elimination as shown below.

35* 3". 7. fl

. + HX
Ph , PH/”\V/~\¢?

Here, "concerted" elimination of HX circumvents the dispro-
portionation step but requires that the leaving group and
the ketyl moieties come into close proximity. The cyclic
haloketones--i.e., BDMBC and CDMBC--were prepared to test
this hypothesis. As listed in Table 18 and illustrated
below, both diastereomers undergo elimination of HX to some

extent.

0
cis-BDMBC H

hv P“
or + HBr

trans - BDM BC

\/

In the trans-diastereomer, X is totally inaccessible
to the benzoyl group; and even in the cis-diastereomer, it
is doubtful whether the required cyclic orientation would

be possible. Therefore, such a cyclic orientation is not

 

105

necessary for photoinduced B-cleavage; however, these
experiments do not preclude product formation from such an
orientation in the acyclic analogues.

Therefore, it seems likely that initial 1,4-biradical
formation followed by rapid B-elimination and in-cage dis-
proportionation is the correct mechanism. The fate of
6-thiophenoxyvalerophenone is shown in Scheme 8 and is

presented to be illustrative of the mechanism.

OH
ks (3. 3%)

8(30. 7%)
34%
«I:

\OH
PMPh ——> 3"[C T] , + -SPh

PhM

coupling 27 7%
products °
100% hv

Ph/H\/\/\5Ph

Type II products

Scheme 8. Photolysis <16 6-Thiophenoxyvalerophenone 1J1
Benzene.

106

Quantum Yields and Other Observations

 

Examination of Table 16 and Scheme 8 reveals that
in the case of 5-SPh, C-T quenching by sulfur is the major
reaction followed by B-elimination to form 4-BB. Inter-
estingly, very small yields of PhSSPh were measured, which at
best comprised only about 3% of the total products. In-cage
coupling of the radicals would result in the situation

shown below, which would probably revert to starting material.

hjj:~/A\// 1 -——-+' O
'SPh
S h

 

 

However, out-of—cage coupling would be statisticalanuiresult ,

in the formation of disulfideanuithe corresponding pinacol.

(fiIOH

OH Ph Ph
2 Ph/i\~/A\¢9’ '—————-9 ;iF—EE
/ \

The small quantum yield of disulfide coupled with the near 100%
material balance allows one to ignore these small side
reactions. However, the fact that they are small means that

very rapid in-cage disproportionation must be taking place.

OH O
.SPh /U\/\
Ph , / ——-—) Ph / + SPh

 

107

In the acyclic cases, the leaving group is already set up
for disproportionation as shown in the previous diagram;
but in the cyclic case, and especially for the trans-
compounds, the leaving group is on the opposite side of the

ring with respect to the ketyl.

q F‘

 

 

 

 

 

Therefore, it must migrate around inside the cage before
disproportionation can occur. In-cage molecular reorgani-

zation must indeed be very rapid.

Rates of B-Elimination

 

Given the plausible assumption that 6-substitution
effects little change in kg,169 comparison of II:4-BB ratios
allows extraction of relative rates of B-elimination.

Table 19 contains the relative rates of B—cleavage for a

variety of groups. Comparison of Cl, Bu, and I reveals the
expected order of ease of elimination--i.e., I > Br > C1-—
which parallels that observed for ionic eliminations.17o

The difference between SR and SPh is roughly a factor

of 1000 in favor of SPh and can be rationalized in terms of

resonance stabilization by the benzene ring, analogous to

 

108

Table 19. Rate Constants of B-EliminatiOn of Various Substit-
uents in G-Substituted Valerophenones.

 

 

 

 

 

Compound k8,108sec-la kBrel
O
H
12th
E.
Cl 0.17 1
Br 1.1 65
I 21.5 1260
SCN 83.0 490
SAC 0.0026 0.15
SBu 0.0029 0.16
SOBu 1.3 76.0
SOzBu 0.0077 0.46
StBu ' 0.0064 0.41
SOPh 10.6 630
SOZPh 0.12 6.8
SPh 1.4 110
aCalculated assuming ks equals 107sec-1.

109

that in a benzylic radical, that is,

are ls .- 1, o:-

The enhanced rate of elimination of SPh relative to RS has
been demonstrated previously171 by the addition of ethane-

thiol to allylphenylsulfide as shown below.

Here elimination of SPh is faster than chain-transfer with
ethanethiol.
The three-fold difference in rates between SBu and

S-tBu can be explained by increased hyperconjugation in the
latter, analogous to that observed for alkyl radicals172 and
the fact that the steric bulk of the t-butyl group lowers
the bond dissociation energy.

Surprisingly, oxidation of the sulfur to a sulfinyl
moiety enhances its rate of elimination relative to the sul-
fide. Thus, the order PhSO > SOBu >> SOzBu and SBu confirms
Kice's173 suggestion that sulfinyl radicals have the greatest
kinetic stability of the three. Sulfinyl radicals have been
thought to be rather stable by analogy with the isoelectronic

nitroxide and dithiyl radicals.174

110

-+
R—S=O 4——) R—S-O- R N—o- (—-—-9 R N—o'

R—S—S- 6——) RS$

Interestingly, S-SCN B-cleaves almost exclusively, whereaijt
5-SAc B-cleavage is a minor product. One might expect
these radicals to be fairly stable by analogy to allyl

radicals.

- sea €——> S=C=N

vs C—C=C «h—a C=C—C
O

H
- S—CCH

0
l
3 (——> S=C—-CH

3

The known lack of conjugative stabilization in a-keto
radicals175 explains the order SCN >> SAc and further indi-
cates the X leaves as a radical since ionic cleavage of
-SAc should be favorable.

The most surprising result of all is that Cl is elimi-
nated faster than SR. Kineticists have assumed a much
smaller value (If kB for C1, and as such one would expect
the observed order to be reversed.176 However, it is
possible that previous studies on monoradicals have indi-
cated too low a value of k8 due to reverse additions. In

the present system rapid in-cage disproportionation tends

to minimize the effects of reversible addition.

111

. . . . . . 177 -
Competitive elimination studies by Hall are

consistent with the present observations. That is, in the

addition of ethanethiol to the allylchloride shown below,

.0

an unexpected product was observed. .
\N EtSvk/Cl EtS
ms + // 1 —'7 +
Cl
72% 28%

The lesser product can be explained by elimination of -C1
followed by ionic addition of HCl to form the observed

product.

 

EEEV/L\¢/Cl'———9 EtS '§§4'Cl- 3FEEV/k\y

C1

Relative rate constants for B-cleavage have not been previ-

ously reported. In fact, the actual rate constants can be

estimated by assuming kS equals 107sec-l.178 This would
yield kB's of lossec-l and lossec-1 for SBu and Br,
respectively.

The corresponding G-phenoxyethers are observed not

to undergo B-cleavage, indicating that ks >> kB in these

Ph/‘(LAA :1, (11A / . no...

112

cases. Cleavage of the comparatively strong C—O bond is
apparently unfavorable. In fact, cleavage in 19, which
would result in the formation of a C-O double bond and a
relatively stable benzhydryl radical, is not observed,

reflecting total kinetic control of the reaction.

ANO Ph hV N + o
P ——> .
h P PhAPh

19

o
I +
P M11 Ph/\Ph

y-Hydrogen Abstraction and Anchimeric Assistance

 

The rate constants of y-hydrogen abstraction for
5-Br and S-I have been found to be enhanced by 230% and 530%,

respectively, relative to that expected if only inductive

179 The observed enhancements were

180

effects were operative.
attributed to anchimeric assistance by the B-haloatom.
Numerous examples of B-halo and B-thiyl assistance are

known.181 Recently, Shevlinl8

2 presented evidence that
suggested a small amount of anchimeric assistance byaphenyl-
sulfinyl group in thetflJ1hydride induced elimination of the
B-bromophenylsulfinyl group. Since the triplet benzoyl

183 only a

group mimics the behavior of alkoxy radicals,
minor effect is noted in the case of S-Br and S-I. The

highly exothermic nature of abstraction of bromine atoms by

113

tin radicals is probably responsible for the small effect
noted in the latter case.

A fairly substantial enhancement in ky.was noted in
Part I for 5-SOBu--rough1y a factor of ten. Assistance by
the sulphinyl group can be envisioned to occur in two dif-
ferent ways in which three-(n:four-centered intermediates
can be constructed. On the other hand, 5-SBu or 5-SPh show

no such enhancements.
‘9
§ or (1-18

The concept of anchimeric assistance requires two
clarifying observations: one, the lowering of the transi-
tive state enthalpy by bridging and greater conformational
restrictions on the structure of the transition state (i.e.,
a more negative AST) require that the temperature dependence
of y-hydrogen abstraction be different than that of a com-
pound in which no bridging is occuring; and, two, stereo-
electronic requirements lead one to expect significant
stereochemical effects on the magnitude of anchimeric assis-
tance, analogous to those observed by Skell184 for axial and
equatorial bromines in a rigid cyclohexyl system.

Figure 17 presents the temperature dependence of the
qu for 6-iodovalerophenone relative to valerophenone. The

fact that the two slopes are different is consistent with

the suggestion that anchimeric assistance is operative.

 

 

114

The effect of orientation upon the magnitude of
anchimeric assistance is striking. Table 20 presents the
kY and km of the various diastereomers of BDMBC and CDMBC.

7 l, which is comparable

The kY for t-CDMBC is 1.1 - 10 sec-
to the kY in 6-chlorovalerophenone. It is faster bya factor
of two in the cyclic case due to the fact that the hydrogens
are perfectly set up for abstraction. However, kY for trans-

8sec-1, a facter of about 200 times

BDMBC is 1.9 - 10
faster. The inductive effect of Br and C1 are comparable18

so the enhanced rate must be due to assistance by Br.

 

Formation of a bridged species as suggested by Skell186 is

possible, but the data do run: permit any comment in this
respect. The trans-isomer is, of course, perfectly set up
for assistance since the C-H and C-Br bonds are trans-

periplanar.187

Conformational Effects

 

Scheme 9 depicts the conformational effects in the
photochemistry of trans-CDMBC. Lewisl88 has previously shown
that when the benzoyl group is axial, only y-abstraction
occurs. Conversely, when it is held equatorially, only
Type I cleavage occurs. Thus, analogous arguments can be

made for the present system. If the respective rates of

 

115

Table 20. Rate Constants of y-Hydrogen Abstraction and
a-Cleavage for the 4-Halo-1,4-Dimethy1-l-
Benzoylcyclohexanes.

 

 

 

- 1 7 -1 7 - 7 -
COmpound ?,10 s kYIlO s ka,10 s
c§ Ph
(0) 2'14 1.11 0.017
(7) 5.07
1
Ch h
(0) 2'40 21.0 0.046
(v)46.7
r
h (a) 2.38 0.92 0.26
5' (y) 7.69
Br
h (0) 2'50 0.77 0.50
U (v) 17.2

 

 

116
Type II Type I
products products
o§ h
-—> c ‘i
(—
h
Cl
Th0 hv
Q§ Ph
———) C]. H
l h
C

Scheme 9. Conformational Effects in the Photochemistry of
trans-CDMBC.

 

117

reaction--i.e., kY and ka--are faster than equilibration of
the excited state conformers, two distinct triplet lifetimes
will be observed (kY and ka can, of course,tx3coincidentally
equal, in which case a single lifetime will be observed).
Thus, product distribution reflects the ground state equili-
brium. Lewis189 has found the Type I quantum yield for 22

in the presence of 0.01M dodecanethiol to be 0.31.

20

Assuming that remote substituents have little effect on 0“.
comparison of the quantum yields of benzaldehyde formation
for the present system should yield the respective ground
state population. Thus, utilizing the quantum yields in
Table 18, the following ground state conformational equili-
bria can be calculated and are presented in Table 21.

Obvisouly, the photochemical results and the corre-
sponding determination of ground state equilibria agree
nicely with the initial predictions and further illustrate
how light can be used as a probe.

On the other hand, prior equilibration of the two
excited conformers would lead to a single lifetime, in which
case the product distribution would depend only upon the
relative rates of y-hydrogen abstraction and a-cleavage.
This, in turn, would reveal little or no information about

ground state equilibria. Complications arising from

 

118

Table 21. Ground State Equilibria of 4-Halo-1,4-Dimethyl-
l-Benzoylcyclohexanes.

 

 

o§ Ph
0
——-0 Cl I
¢______ Ph
Cl
99% 1%
(he Ph ,
0
'—"° Br ; : 5 H
i Ph
r
94% 6%
(h: Ph Br
0
Br 5 ||
*— Ph
61% 39%

 

 

119

intermolecular energy transfer from one excited conformer
to the other are not likely here in light of the low concen-

tration used and the short triplet lifetimes.

Indications for Further Research

Synthetic Utility. The synthetic utility of this

 

reaction as a means of introducing double bonds in a highly
regiospecific manner needs to be investigated.

Relative Rates of B-Cleavage. This reaction provides

 

an excellent handle for measuring relative rates of k8 for
various groups. However, it presents a serious limitation

in that kS is too fast to allow elimination of other less
stable radicals--i.e., -OPh and -CH2Ph. Perhaps, if ks

could be slowed down, the utility of the reaction could be
enhanced. Utilization of the thioester derivatives might
accomplish this since formation of a C-S double bond is fairly

unfavorable. However, a-cleavage would probably be a

Type II

///3 products
‘\\\9 B-cleavage

0 OH
Ph/\s x ——) Ph - s/\/\x

competing reaction. Stabilization of the ketyl radical

moiety as shown below might also serve to decrease ks.

 

120

B-Substituted Butyrophenones. Analogous B-cleavage
should also be observable for B-substituted butyrophenones

as shown below.

OH )(

0
ll
PhM __9 PhN§

0

These systems have not been previously investigated. A
cyclic concerted mechanism as mentioned before should be
more favorable for this system relative to the 6-substituted
valerophenones.

Inductive Effects. An investigation into the effects
of stereochemistry upon inductive effects would be
interesting. For instance, comparison of the following two
isomers would allow detection of any difference in the
inductive effect upon y-hydrogen abstraction between the

axial and equatorial chlorines.

0%. Ph
Cl
Qb £01

C1

EXPERIMENTAL

Preparation and Purification of Materials

 

Solvents and Additives

 

Benzene: (Mallinckrodt) was purified by stirring over
concentrated sulfuric acid for several days. The benzene
was then washed with additional amounts of sulfuric acid
until it remained clear, followed by several washings with
water and one final washing with saturated sodium bicar-
bonate. The benzene was dried over magnesium sulfate or
sodium sulfate and distilled from P205 through :1 column
packed with glass helices. Only the middle 50% was collected.

Methanol: (Fisher Scientific or Mallinckrodt) was

 

distilled from magnesium turnings. The middle fraction was
collected.

Dioxane: (Mallinckrodt) was used as received or
distilled through a short Vigreux column.

Pyridine: (Mallinckrodt) was distilled from barium

 

oxide and the middle fraction collected.

Acetonitrile: (Fisher) was distilled rapidly from

 

potassium permanganate. Sulfuric acid was added to the
distillate and the distillate was decanted from the ammonium

salts. It was then distilled throughaishort Vigreux column.

121

122

Ethanol: was used as received.

Hexane: (Mallinckrodt) was used as received.

Pentane: (Mallinckrodt or Drake Brothers) was used
as received.

Benzenethiol: (Aldrich) was used as received.

 

Internal Standards

 

The standards used in this work were purified by
Dr. P. J. Wagner as indicated below.

Dodecane: (Aldrich) was purified in the same manner

 

as benzene with distillation under reduced pressure.

Tetradecane: (Columbia Organics) was purified in the

 

same manner as dodecane.

Hexadecane: (Aldrich) was purified in the same

 

manner as dodecane.

Heptadecane: (Aldrich) was purified in the same man-

 

ner as dodecane.

Octadecane: (Aldrich) was purified by recrystalliza-

 

tion from ethanol.

Nonadecane: (Chemical Samples) was purified in the

 

same manner as octadecane.

Quenchers

 

Ngthalene: (Matheson Coleman and Bell) was recrystal-

 

lized several times from ethanol.

l-Methylnapthalene: (Aldrich) was used as received.

 

123

Cis- and Trans-1,3-Pentadiene: (Chemical Samples)

 

was used as received.

Cis-l,3-Pentadiene: (Chemical Samples) was used as

 

received and found to be 99.8% pure by vpc.

n-Butylsulfide: (Aldrich) was used as received.

 

n-Butylsulfoxide: was prepared by 30% hydrogen

 

peroxide oxidation of n-butylsulfide in acetone. It was puri-
fied by recrystallization from hexane.

n-Butylsulfone: was prepared by 30% hydrogen peroxide

 

oxidation of n-butylsulfide in glacial acetic acid. It was

purified by recrystallization from hexane.

Ketones
Acetophenone: (Matheson Coleman and Bell) was dis-
tilled under reduced pressure by A. E. Puchalski.

Valerophenone: was prepared by the Friedel-Crafts

 

acylation of benzene by valeryl chloride. The acid chloride
was dripped alowly into a mixture of a ten-fold excess of
benzene containing a 5% excess of aluminum chloride at O—SOC
and stirred for 3-10 hours. The mixture was then poured

onto cracked ice and concentrated HCl and the layers separated.
The benzene layer was washed several times with dilute HCl,
dried over sodium sulfate and evaporated under aspirator
pressure. The crude produce was distilled under reduced
pressure and the middle fraction collected.

Butyrophenone: (Aldrich) was purified by Dr. M. J.

 

Thomas.

124

Phenacylchloride: (Aldrich) was used as received.

 

Phenacylbromide: (Aldrich) was used as received.

 

B-Bromopropiophenone: was prepared by the Friedel-

 

Crafts acylation of benzene with B-bromopropionyl chloride
in carbon disulfide at -5-0°C in an analogous manner as
valerophenone: NMR(CDC13) 3.2(m,4H), 7.2(m,3H), 7.8(m,2H).

y-Chlorobutyrophenone: was prepared by the Friedel-

 

Crafts acylation of benzene by y-chlorobutyryl chloride
(Aldrich) in the same manner as valerophenone: NMR(CDC13)
200(m’2H), 300(t’2H), 3.5(t'2H), 7.2(m,3H), 7.8(m,2H).

6-Chlorovalerophenone: was prepared by J. H. Sedon.

 

e-Chlorohexanophenone: was prepared by W. B. Mueller.

 

Phenacylsulfides: (General Procedure) were prepared

 

by treatment of the appropriate phenacyl chloride or bromide
with the sodium salt of the corresponding thiol. The appro-
priate alkylthiol or arylthiol was added to an ethanolic
NaOH solution and stirred for one hour. The phenacyl halide
(one equivalent) was added in one portion, and a mild exo-
thermic reaction ensued. The mixture was stirred overnight
at room temperature and poured into water. It was then
extracted with several portions of ether. The combined
ether extracts were washed several times with water, dried
over sodium sulfate and evaporated. The crude products were
either distilled at reduced pressure or recrystallized from
ethanol. The following compounds were prepared in this

manner .

125

2-Thiomethylacetophenone (Z-SMe): bp 80°C(0.05mm);

IR(neat) 2900, 1655, 1360cm"1

; NMR(CDC13) 62.05(s,3H).
6.05(s,2H), 7.3(m,3H), 7.8(m,2H); m/e 166(M+).
2-Thiobutylacetophenone (2-SBu): bp 120°C(0.50mm);
IR(neat) 2950, 1690, 12750m’1; NMR(CDC13) 60.9(m,3H),
1.4(m,4H), 2.5(t,2H), 3.7(s,2H) 7.3(m,3H) 7.8(m,2H);
m/e 208(M+). .
2-Thio-t-butylacetophenone (2-StBu): bp 100°C(0.05mm);
IR(neat) 2950, 1695, 1280cm-1; NMR(CDC13) 61.3(s,9H),
3.8(s,2H), 7.3(m,3H), 7.8(m,2H); m/e 208(M+).
2-Thiophenylpropiophenone (s-ZSPh): bp 135°C(0.05mm);
IR(neat) 3025, 1695, 1230cm—l; NMR(CDC13) 61.5(d,3H),
4.5(m,1H), 7.2(m,8H), 7.8(m,2H); m/e 242(M+).
2-Thiophenylisobutyrophenone (t-ZSPh): bp 130°C

(0.07mm); IR(neat) 3025, 1695, 1230001‘1

; NMR(CDC13)
61.5(s,6H),7.3(m,8H), 8.2(m,2H); m/e 256(M+).
Phenyldesylsulfide (PDS): mp 77°C; NMR(CDC13)
65.7(s,lH),7.2(m,13H), 7.8(m,2H); m/e 304(M+).
I 2-Thiophenylacetophenone (2-SPh): mp 49°C; IR(CHC13)

3000, 1685, 1605, 120500?1

; NMR(CDC13) 64.2(s,2H), 7.2(m,8H),
7.8(m,2H); m/e 228(M+).
2-Thiophenyl-4'-fluoroacetophenone (F-ZSPh):
bp 150-55°C(0.25mm); IR(neat) 3000, 1685, 1605, 1205cm'1;
NMR(CDC13) 64.05(s,2H), 7.08(m,8H), 7.8(m,2H); m/e 246(M+).
2-Thiophenyl-4'-cloroacetophenone (Cl-ZSPh): mp 65°C;
IR(CHC13) 3000, 1680, 1600, 12750m'1; NMR(CDC13) 64.1(s,2H),

7.1(m,8H), 7.7(d,2H); m/e 262(M+).

126

2-Thiophenyl-4'-bromoacetophenone (Br-ZSPh): mp 60°C;

IR(CHC13) 3000, 1680, 1595, 1280cm‘l

; NMR(CDC13) 64.1(s,2H),
7.1(m,5H), 7.5(m,4H); m/e 307(M+).
2-Thiophenyl-4'-methylacetophenone (Me-ZSPh): nm>61°C;
IR(CHC13) 3000, 1660, 1605, 1275cm'1; NMR(CDC13) 62.3(s,3H),
4.1(s,2H), 7.1(m,8H), 7.6(d,2H); m/e 242(M+).
2-Thiophenyl-4'-methoxyacetophenone (OMe-ZSPh):
mp 86°C; IR(CHC13) 3000, 1670, 1600, 1265cm-1; NMR(CDC13)
63.7(s,3H), 4.1(s,2H), 6.8(d,2H), 7.1(m,5H), 7.8(d,2H);
m/e 258(M+).
2—Thiophenyl-4'-thiomethylacetophenone (SMe-ZSPh):
mp 48°C; IR(CHC13) 3000, 1670, 1590, 1095cm-l; NMR(CDC13)
62.4(s,3H), 4.2(s,2H), 7.1(m,8H), 7.6(d,2H); m/e 274(M+).
2-Thiopheny1-4'-cyanoacetophenone (CN-ZSPh): mp 65°C;
IR(CHC13) 3000, 2225, 1700, 1275cm-l; NMR(CDC13) 64.2(s,2H),
7.2(s,5H), 7.7(m,4H); m/e 253(M+).
2-Thiophenyl-4'-phenylacetophenone (0-28Ph): mp 92°C;
IR(CHC13) 3000, 1700, 1275cm-l; NMR(CDC13) 64.2(s,2H),
7.0-7.5(m,12H), 7.8(d,2H); m/e 304(M+).
2-Thiophenyl-4'-dimethylaminoacetophenone (NMez-ZSPh):
was prepared by the reaction of dimethylamine and 2-thiophenyl-
4'-f1uoroacetophenone. 109 of 2-thiophenyl-4'-fluoroaceto-
phenone was dissolved in 50ml of xylene and placed in a pres-
sure bomb. The bomb was cooled in an ice-salt bath, and 25ml
of anhydrous dimethylamine (Aldrich) was added. The bomb

was sealed and heated at 80°C for 24 hours with vigorous

stirring. The bomb was cooled before opening, and the

127

mixture was worked up as in the general procedure for the,
phenacylsulfides. The crude product was crystallized from
ethanol and obtained pure in 85% yield: mp 78°C; IR(CHC13)
3000, 1660, 1600, 1375cm-l; NMR(CDC13) 62.9(s,6H), 4.1(s,2H),
6.5(d,2H), 7.1(m,5H), 7.7(d,2H); m/e 271(M+).
l-Benzoyl-l-thiophenylcyclopropane (cy-ZSPh): was
prepared by the reaction of sodium thiophenoxidevfiifll2-bromo-
4-chlorobutyrophenone and subsequent base cyclization. 28g
of 2-bromo-4-chlorobutyrophenone obtained by the bromination
of 4-chlorobutyrophenone was dissolved in 100ml of ethanol.
To this was added one equivalent of sodium thiophenoxide,
and this was allowed to stir for four hours. A slight excess
of sodium methoxide was added in one portion to effect
cyclization, and the product worked up as in the phenacyl-
sulfides. Recrystallization from ethanol gave a 91% yield
of pure product: mp 62°C; NMR(CDC13) 61.3(m,2H), 1.7(m,2H),
7.2(m,8H), 7.8(m,2H); m/e 254(M+).
4'-thiophenylmethylacetophenone (4'-MSPh): was pre-
pared from sodium thiophenoxide and 4'-bromomethylacetophe-
none. 4'-bromomethylacetophenone was obtained by irradiation
of a mixture of 40g 4'-methylacetophenone and 53g n-bromo-
succinimide in 500ml carbon tetrachloride. Pure bromide was
obtained by fractionation at reduced pressure in about 30%
yield. The reaction of sodium thiophenoxide and 4'-bromo-
acetophenone was carried out in the same manner as the
phenacylsulfides. Pure product was obtained from ethanol in

a 95% yield: mp 91°C; IR(CHC13) 3000, 1685, lzsscm‘l;

128

NMR(CDC13) 62.5(s,3H),-4.l(s,2H), 7.2(m,8H), 7.7(d,2H);
m/e 242(M+).

Benzoylsulfides: (General Procedure) were prepared

 

essentially the same as the phenacylsulfides except that the
reaction mixtures were refluxed for a period of 5-12 hours.
In the case of 6-benzoylsulfides, the carbonyl group of
4-chlorobutyrophenone was protected by forming the ethylene
glycol ketal prior to reaction with sodium thiolates; other-
wise, good yields of phenylcyclopropylketone were obtained.
Intramolecular cyclization of the haloketones was only found
in the case of 4-chlorobutyrophenone. The ketal was then
hydrolyzed by vigorous stirring in 15% HCl overnight. The
products were either distilled under reduced pressure or
recrystallized from ethanol. The following compounds were
prepared in this manner.

3-Thiobutylpropiophenone (3-SBu): bp l30-150°C
(aspirator); IR(neat) 2950, 1680, 1450, 135000‘1; NMR(CDC13)
60.9(m,3H), l.4(m,4H), 2.4-3.4(m,6H), 7.3(m,3H), 7.8(m,2H);
m/e 222(M+).

4-Thiobutylbutyrophenone (4-SBu): bp 145°C(0.3mm);
IR(neat) 2950, 1695, 1450, 12300m‘1; NMR(CDC13) 60.9(m,3H),
l.4(m,4H), 1.9(m,2H), 2.5(m,4H), 3.l(t,2H), 7.3(m,3H),
7.8(m,2H); m/e 236(M+).

4-Thio-t-butylbutyrophenone (4—StBu): bp 125°C
(0.15mm); IR(neat) 2950, 1695, 1225cm’1: NMR(CDC13)
61.25(s,9H), 2.0(m,2H), 2.6(t,2H), 3.1(t,2H), 7.3(m,3H),

7.8(m,2H); m/e 236(M+).

129

4-Thiophenylbutyrophenone (4-SPh): mp 35°C; IR(CHC13)

2990, 1675, lzzscm"l

; NMR(CDC13) 62.0(m,2H), 3.0(M,4H),
7.2(m,8H), 7.8(m,2H); m/e 254(M+).
5-Thiobutylvalerophenone (5-SBu): bp 155°C(0.3mm);

IR(neat) 2930, 1685, 1450, lzzocm"l

; NMR(CDC13) 60.9(m,3H).
l.6(m,8H), 2.4-3.0(m,6H), 7.3(m,3H), 7.8(m,2H); m/e 250(M+).
S-Thio-t-butylvalerophenone (S-StBu): bp 140°C
(0.06mm); IR(neat) 2950, 1695, 1220cm'1; NMR(CDC13) 61.2(s,9H),
l.7(m,4H), 2.5(t-2H), 2.9(t-2H), 7.3(m-3H), 7.8(m—2H):
m/e 250(M+).
5-Thiopheny1valerophenone (5-SPh): mp 87°C; IR(CHC13)

2995, 1675, 1200cm'l

; NMR(CDC13) 51.9(m,4H) , 2.9(t,4H) ,
7.3(m,8H), 7.8(m,2H); m/e 270(M+).
6-Thiobutylhexanophenone (6-SBu): bp 145-160°C

(0.4-0.5mm); IR(neat) 2930, 1695, 1450, 1220001“1

; NMR(CDC13)
6009<mp3H)’ 1.2-1.9(m'10H)’ 2.5(t-4H)’ 2.9(t-2H)' 7.3(m,3H),
7.8(m,2H); m/e 264(M+).

Benzoylsulfoxides: (General Procedure) were prepared

 

by hydrogen peroxide oxidation of the corresponding benzoyl-
sulfide. The benzoylsulfide was dissolved in acetone, and
one equivalent of 30% H202 was added carefully behind safety
shield. The solution was allowed to stir in dim light over-
night. The solvent was evaporated at reduced pressure, and
the crude crystalline product was recrystallized from ether:
chloroform. The following compounds were prepared in this manner.
3-Butylsulfinylpropiophenone (3-SOBu): mp 78oc;

l

IR(CHC13) 2950, 1695, 1225, lozscm' ; NMR(CDC13) 60.9(m,3H),

l.2-l.9(m,4H), 2.5-3.5(m,6H), 7.3(m,3H), 7.8(m,2H) ; m/e 238(M+) .

130

4-Butylsulfinylbutyrophenone (4-SOBu): mp 47°C;
IR(CHC13) 2950, 1698, 1225, 1030cm-l; NMR(CDC13) 50.9(m,3H),
l.2-2.0(m,4H), 2.2(m,2H), 2.7(m14H), 3.2(t-2H), 7.3(m,3H),
7.8(m.2H); m/e 252(M+).

5-Butylsulfinylvalerophenone (5-SOBu): mp 79°C;
IR(CHC13) 2950, 1695, lolocm‘l; NMR(CDC13) 60.9(m,3n).
l.2-2.0(m,8H), 2.6(t,4H), 3.8(t,2H), 7.3(m,3H), 7.8(M,2H);
m/e 266(M+).

S-Phenylsulfinylvalerophenone (5-SOPh): mp 60°C;
IR(CHC13) 3000, 1698, 10500m’1; NMR(CDC13) 61.8(m,4H),
2.9(m,4H), 7.3(m,8H), 7.8(m,2H); m/e 286(M+).

Benzoylsulfones: (General Procedure) were preparedtnr

 

the oxidation of the corresponding sulfoxide or alterna-
tively the corresponding sulfide. A large excess of 30%
H202 was added behind a safety shield to either the benzoyl-
sulfide or benzoylsulfoxide in glacial acetic acid. The mix-
tures were allowed to stir for one or two days and then
poured into H20. The aqueous mixture was extracted several
times with chloroform. The chloroform layer was washed
several times with H20 and finally once with saturated sodium
bicarbonate to remove the last traces of acetic acid. The
CHCl3 layer was then dried over sodium sulfate and evaporated.
The crystalline products were purified in the same manner
as the benzoylsulfoxides. This procedure was used for the
following compounds.

3-Butylsu1fonylpropiophenone (3-SOZBu): mp 116°C;
IR(CHC13) 2950, 1695, 1315, 1225, llZScm-l; NMR(CDC13)

 

131

60.9(m,3H), l.2—2.0(m,4H), 3.0(t,2H), 3.4(m,4H), 7.3(m,3H),
7.8(m,2H); m/e 254(M+).
4-Butylsulfonylbutyrophenone (4-SOzBu): mp 65°C;

IR(CHC13) 2950, 1695, 1300, 11250m‘l

; NMR(CDC13) 60.9(m,3H),
1.2-2.5(m,6H), 2.8(m,6H), 7.3(m,3H), 7.8(m,2); m/e 268(M+).
5-Butylsu1fonylvalerophenone (5-SOzBu): mp 66°C;

IR(CHC13) 2950, 1700, 1300, 1125010"1

; NMR(CDC13) 60.9(m,3H),
l.5-2.1(m,8H), 3.0(m,6H), 7.4(m,3H), 7.8(m,2H); m/e 282(M+).
5-Pheny1sulfonylvalerophenone (5-SOZPh): mp 90°C;

IR(CHC13) 2950, 1695, 1305, 1150010“1

; NMR(CDC13) 61.9(m,4H);
3.0(m,4H), 7.3(m,8H), 7.8(m,2H); m/e 302(M+).
2-Methylsulfinylacetophenone (2-SOMe): was prepared
by a slight modification of the method of Corey and
Chaykovsky.”0 To a slurry of 37g potassium t-butoxide in
200ml DMSO was added 50g ethylbenzoate dropwise. The reac-
tion micture was maintained at about 70°C for one hour with
vigorous stirring. The mixture was then poured into ice-
water and acidified with concentrated HCl. The entire mix-
ture was extracted with CHCl3 and worked as in the benzoyl-
sulfoxides. The product was obtained in 70% yield as
needles from ether-CHC13: mp 84°C; IR(CHC13) 3000, 1680,

l

1275, losocm' ; NMR(CDC13) 62.7(s,3H), 4.3(s,2H), 7.3(m,3H),

7.8(2,H).

2-Methylsulfonylacetgphenone (2-SO Me): was prepared

2
in the same manner as 2-SOMe except that the slurry also

 

contained a 10% excess of dimethylsulfone (Aldrich) relative

to ethylbenzoate. Recrystallization from ether-CHCl3

132

afforded a 75% yield: mp 105°C; IR(CHC13) 3000, 1695,
132500‘1; NMR(CDC13) 63.1(s,3H), 4.5(s,2H), 7.3(m,3H),
7.8(m,2H); m/e 198(M+).

5-Thioacetoxyvalerophenone (5-SAc): was prepared
by the free radical addition of thioacetic acid to 4-benzoyl-
butene. A two-fold excess of thiolacetic acid was added to
4-ben20ylbutene (prepared by Dr. M. J. Thomas) and was
refluxed overnight in benzene with a "pinch" of benzoyl
peroxide. The mixture was washed with aqueous sodium
bisulfite and worked up in the same manner as the benzoyl-
sulfoxides. It was recrystallized from ethanol: mp 63°C;

IR(CHC13) 3000, 1690, 122000?1

; NMR(CDC13) 51.7(m,4H),
2.9(m,4H), 2.2(s,3H), 7.3(m,3H), 7.8(m,2H); m/e 236(M+).

5-Thiocyanatovalerophenone (5-SCN): was prepared
191

 

as described by Dr. B. J. Scheve.
t-4-Chloro-1,4-dimethyl-l-Benzoylcyclohexane:(t-CDMBC):
was prepared by the addition of HCl to 1,4-dimethy1-l-
benzoylcyclohex-3-ene (DMBC). 40g methyl methacrylate was
dripped into 250ml benzene containing 5g of AlCl3. 289 of
isoprene was added slowly, and the mildly exothermic reac-
tion was cooled in a water bath. It was allowed to stir
overnight and worked up in the same manner as valerophenone.
This procedure yielded a 80% crude yield of the olefin which
was used without further purification. This was then hydro-
lyzed to the acid by refluxing in a 50:50 ethanol/water
solution containing an excess of KOH. The solution was
cooled and acidified with concentrate HCl. The precipitated

acid was collected by suction filtration and washed with

133

copious amounts of water. The crude crystals were then
recrystallized from hexane and obtained:h190% yield. The
product was identified by its melting point, which was found
to be identical to the literature value--i.e., 69°C.

The phenylketone was prepared by addition of two
equivalents PhLi (Aldrich) to an ethereal solution of the acid
followed by refluxing for three hours. The homogeneous
solution was poured into water, and the layers separated.
The ether layer was washed with water, dried over sodium
sulfate, and evaporated. Attempts at vacuum distillation
resulted in decomposition and polymerization, so the product
was used without further purification.

DMBC was then dissolved in glacial acetic acid and
dry HCl was bubbled through until the olefinic protons
disappeared in the nmr. The product mixture was then poured
into water and extracted with chloroform. The chloroform
layer was washed with water and followed by one washing with
saturated sodium bicarbonate. It was then dried over sodium
sulfate and evaporated. Addition of pentane to the crude
oil followed by cooling and scratching with a glass rod
resulted in crystallization. The product was identified as
t-CDMBC by a X-ray crystal structure. The nmr spectrum
appears in Figure 14: mp 65°C; IR(CHC13) 2920, 1670, 1500,

1; m/e 250(M+); the 13

1275cm- C spectrum appears in Figure 18 .
cis-anuitrans-4-Bromo-l,4-dimethyl-l-benzoylcyclo-

hexane (cis- and trans-BCMBC) : was prepared in the same manner

as trans-CBMBC except that HBr was used instead of HCl. It was

then found that after the initial crop of crystalswas collected,

134

concentration of the mother liquor and subsequent cooling

resulted in the formation of another crop of crystals. These
two crops were later found to be the cis and trans isomers, respec-
tively. The assignment of these structures was discussed in
the results section of 6-substituted valerophenoneileart II.

The nmr spectra are presented in Figures 15 and 16, and the

13C spectra are presented in Figures 19 and 20: trans-BDMBC--

mp 82°C; IR(CHC13) 2950, 1660, llecm'l; m/e 295(M+)--

1

c-BDMBC--mp 32°C; IR(CHC13) 2930, 1675, 1205cm’ ; m/e 295(M+).

4'-Methoxye5-chlorovalerophenone (OMe—S-Cl): was

 

prepared by Dr. P. J. Wagner.

4'-Trif1uoromethyl-5-chlorovalergphenone (CF3-5-Cl):

 

was prepared by the addition of 5-chlorovaleronitrile

(Aldrich) to 4-trifluoromethylphenylmagnesiumbromide:

bp 105°C(0.05mm); IR(neat) 2950, 1701, 1340, 114SCm-l

‘0

NMR(CDC13) 61.9(m,4H), 3.0(m,2H), 3.5(m,2H), 7.5(d,2H),
7.8(d,2H); m/e 264(M+).

5-Iodovalerophenone (S-I): was prepared by J. H.
Sedon.

5-(4'-Methoxy){phenoxyvalerqphenone (S-OPh): was
prepared by the reaction of 5-I with the sodium salt of
p-methoxyphenol. To a DMSO solution containing freshly cut
sodium was added one equivalent of p-methoxyphenol. It was
allowed to stir until consumption of the sodium was complete.
One equivalent of 5-I was added, and the mixture heated at
100°C for four hours. The mixture was then poured into H20

and extracted with ether. The combined ether extracts were

washed several times with H20, dried over sodium sulfate,

135

and evaporated. The crude product was recrystallized in
hexane in low yield: mp 47°C; NMR(CDC13) 61.9(m,4H),
3.0(m,2H), 3.7(s,3H), 3.9(m,2H), 6.6(d,4H), 7.3(m,3H),
7.8(m,2).

4-Benzhydryloxybutyrophenone (4-OBzhyd1): was pre-

 

pared by the addition of phenylmagnesiumbromide to the
appropriate nitrile. The nitrile was prepared by refluxing
429 trimethylenechlorohydrin in 35ml benzene containing 5m1
concentrated H2804 and 55g benzhydrol for eight hours. The
mixture was washed with H20, dried over sodium sulfate, and
evaporated to give a near quantitative yield of benzhydryl-
oxypropylchloride. This was converted to the nitrile
directly by heating at 100°C in DMSO with a 20% excess of
NaCN. Aqueous workup, followed by drying over sodium sulfate,
yielded 4-benzhydryloxybutyronitrile, which was used without
further purification. The Grignard Reaction with phenylmag-
nesiumbormide proceeded smoothly. Recrystallization from
heptane resulted in a low yield: mp 74°C; NMR(CDC13)
62.0(m,2H), 3.0(t,2H), 3.5(t,2H), 5.2(2,1H), 7.2(m,13H);
7.8(m,2H); m/e 330(M+).

Techniques

 

Preparation of Samples

 

Photochemical Glassware. All photochemical glassware,

 

including class "A" pipets and class "A" volumetrics, were
heated for a day or two in aqueous ammonium hydroxide,

followed by rinsing and heating in distilled water, followed

136

finally by prolonged drying in a 160°C oven. Photolysis
tubes (131:100mm culture tubes) were washed in a analogous
manner, and the necks elongated by rotation in a flame and
pulled until the desired length was attained.

Stock Solutions and Photolysis Solutions. All solu-

 

tions were prepared either by weighing the desired amount of
substrate directly into the volumetric flash and diluting to
the line with the appropriate solvent, or by pipetting an
.aliquot of a stock solution into the volumetric and diluting
to the appropriate volume.

Quantum Yields, Quenching, and Sensitization Studies.

 

All solutions were prepared as described above. A 5cc
syringe fitted with a 6" needle was used to transfer 3.8ml
of the solution to the test tube with the constricted neck.

Degassing. After the tubes were filled with the

 

appropriate solutions, they were attached via one-holed
rubber stoppers (size 00) directly to a vacuum line. The
solutions were then frozen by slow immersion in liquid nitro-
gen. When the tubes were completely immersed and frozen, the
stopcocks were opened, and the tubes were pumped on for
about five to ten minutes. The stopcocks were then closed,
the liquid nitrogen was removed, and the tubes were allowed
to thaw either by standing in the air or by immersionjxtcool
water. This process, known as a "freeze-thaw cycle," was
typically repeated a total of three times. On the final
cycle, the tubes were sealed by a torch while they were

frozen and open to the vacuum line.

137

Irradiation Procedures

 

Kinetic Runs. The degassed tubes were thawed and

 

mixed thoroughly and wiped clean. Samples to be irradiated
were then placed in a rotating merry-go-round apparatus
which was immersed in a water bath held at 25°C. All tubes
were irradiated in parallel to insure that each sample
obtained an equal amount of light. The light source was a
450-watt (Hanovia) medium-pressure lamp, cooled by a quartz
or pyrex immersion well. The 313nm region was isolated by
employing a filter solution composed of 0.0002M potassium
chromate in 1% potassium carbonate. The 366nm region was
isolated by employing a set of Corning #7-83 filters.

Preparative Runs. Preparative photolysis runs were

 

carried out in quartz or vycor immersion wells utilizing

a pyrex filter around a 450-watt (Hanovia) medium-pressure
lamp. Nitrogen was bubbled in vigorously through a subsur-
face inlet prior to irradiation,enuia positive pressure was
maintained above the solution during photolysis. Typically
160ml of 0.05-0.2M solutions were irradiated. The solutions
were irradiated varying lengths of time, depending upon the
quantum yields and desired conversions, and were followed

by vpc when possible.

Analysis of Samples

 

Identification of Photoproducts. Photoproducts were

 

identified by isolation via preparative vpc, comparison of

vpc retention times with authentic samples, or nmr.

138

Acetophenones were identified by comparison of their
retention times with those of authentic samples under
identical conditions. In the cases of 4-SBu, 2-SPh, and
5-SPh, acetophenone was isolated by preparative Vpc.

4—Benzoyl-l-butene (4-BB) was identified by photolysis
of a 0.05M solution of ketone in benzene as previously
described for 24 hours. Evaporation of the benzene under
reduced pressure yielded a brown oil. Vpc analysis showed
essentially one peak, which had an identical retention time
to an authentic sample of 4-BB. Isolation of that peak was
effected by preparative vpc, utilizing a 10% SE-30 column
at 160°C. The isolated compound was shown to be 4-BB by
comparison of spectral data.

Butylbutanethiolsulfonate was identified by vpc
retention time comparison with an authentic sample prepared
by the method of Majeti.192 A

Diphenyldisulfide was identified by vpc retention
time comparison with an authentic sample prepared by the
addition of 12 to a methanolic solution of benzenethiol.

l,4-Dimethyl-l-benzoylcyclohex-3-ene (DMBC) was identi-
fied by three methods. Since the 4-halo-l,4-dimethyl-l-
benzoylcyclohexanes are unstable to vpc analysis and chroma-
tography on silica or alumina, direct isolation of the
olefin was impossible. However, three indirect methods
provided substantial evidence for the production of DMBC in the
photolysis of trans-CDMBC and cis- and trans-BDMBC. The first

(Method I) involved photolysis of trans-CDMBC until it was

139

completely consumed. Injection of trans-CDMBC onto a 3% QF-l

column at 150°C resulted in two peaks as pictured below.

#2

N

Peak #1 was identical with DMBC; peak #2 was assumed to be
the chloride. After about 12 hours of photolysis, peak #2

had disappeared and a new peak (#3) had appeared as shown below.

#1
#3

 

 

Peak #3 was assumed to be the bicyclic alcohol resulting from
y-hydrogen abstraction. A fairly intense absorption in the
IR at 3500cm-l was observed for the crude photolysate.
Derivatization of the photolysate formed the basis for identi-
fication by Method II. The benzene was removed by rotary

evaporation and the crude oil dissolved in CCl Addition of

4.
bromine resulted in the precipitation of an orange solid,
which melted at 79°C. An authentic sample of the dibromide
was prepared in an analogous fashion from authentic DMBC.
This compound melted at 83°C and was judged to be identical
to the photolysate addition product. The photolysate Br2 addi—
tion product was found to yield DMBC upon zinc dust

140

debromination (vpc), whereas injection of the dibromide on
the vpc resulted in no DMBC formation. Lastly, Method III
involved identification of DMBC by nmr. A dilute solution

of t-BDMBC in benzene-d6 containing 0.05M pyridine was

placed in an nmr tube and degassed by one freeze-thaw cycle.
After several hours of irradiation at 313nm, a white preci-
pitate, which was assumed to be pyridinium hydrobromide, had
formed; and the nmr possessed some vinylic absorptions, which
were assumed to arise from DMBC.

Benzaldehyde was identified by comparison of its vpc
retention time with that of an authentic sample.

Gas Chromatography Procedures. Analyses for all
photoproducts were made on either an Aerograph Hy-Fi model
600D gas chromatograph or a Varian Aerograph 1200 gas
chromatograph. Recorders were used interchangeably but were
either a Leeds and Northrup Speedomax-H recorder or a
Sargent Model SR recorder. Each of the instruments were
prepared for on-column injection and utilized nitrogen as the
carrier gas. Both used flame ionization detectors and were
connected to a Infrotronics Automatic Digital Integrator
Model CRS 309. Sample injections were made via a Hamilton
syringe using varying amounts from 0.02-0.2 microliters per
injection. All analyses were made on one of the following
columns:

-- Column #1: 6' x1/8" aluminum containing 3% QF-l

on 60/80 chromosorb G.
-- Column #2: 6' x1/8" aluminum containing 5% SE-30

on 60/80 chromosorb W.

141

-- Column #3: 10':<1/8" aluminum containing 25%
Carbowax 20m on 60/80 chromosorb G.

-- Column #4: 25')<l/8" aluminum containing 25%
1,2,3-Tris(2-cyanoethoxy)propane on 60/80 chromo-
sorb W.

Actinometry andQQuantum Yields. Photoproduct concen-

 

trations were easily determined using vpc productzinternal
standard ratios. A correction factor (CF) to correct for
the difference in molar responses for the different com-
pounds was determined by measuring the relative vpc peak
areas of products and standards of known concentrations.
Thus, the concentration of the appropriate photoproduct can
be determined from the following equation:

area product

[prod.] = CF °[lnt‘ stand.] 'area int. stand.

 

The CF's will be listed in the Appendix.

Valerophenone actinometry was used exclusively for
all quantum yields and ketone disappearance yields. A 0.1M
solution of valerophenone in benzene containing as known
amount of hexadecane was irradiated in parallel with the
desired compound. Analysis for acetophenonewas made using
column #1. The known quantum yield of a 0.1M valerophenone
solution is 0.33.193 The quantum yield for product forma-
tion was determined via the following euqation:

[prod.]

q, ._._ ° 0.33
prod - [acet. ]va1

 

142

val refers to the concentration of acetophenone

where [acet.]
formed in the valerophenone actinometer.

Disappearance yields were determined by comparing
ketone:standard ratios before and after irradiation. This
fraction multiplied by the initial concentration of ketone
yields A[ketone] which, when plugged into the following
equation, yields ¢_K.

before

after
(ketone) /,(ketone

stand. stand.)

initial _ initial = A[ketone]

R- [ketone] [ketone]

A[ketone]

val. 0.33

 

¢7K — [acet.]
Cis-l,3-pentadiene sensitization plots were construc-
ted to determine the intersystem crossing yields and in
cases where no product was formed, the triplet lifetime.
Tubes containing 0.05M ketone with varying amounts of c-l,3-
pentadiene were irradiated in parallel withaltube containing
0.1M acetophenone and 1M c-l,3-pentadiene. Actual quantum

yields of c+t were calculated in the following manner:

[trans] = B'[cis]

 

, _ 0,55
where B - 0.551n0.55 _ B
_ R = area t
and B ——R + l where R _area c

143

 

actinometer
Thus, I = [trans]_1
0.55
ketone
Then, ¢ = [trans]
c+t I

 

A plot of 0.55/0c+t versus l/[c-1,3-pentadiene] yieldsailine
in which the reciprocal of the intercept equals ¢isc and the

intercept divided by the slope equals qu.

Spectra

Proton magnetic resonance (nmr) spectra were recorded
on a Varian T-60 spectrometer as CCl4 or CDCl3 solutions
utilizing TMS as an internal standard. 13C spectra were
recorded on a Varian CFT-20 spectrometer utilizing the usual
Fourier transform signal enhancement with broad band proton
decoupling. Spectra were run in CHC13, which also served as
a lock. Infrared spectra were recorded on a Perkin-Elmer
237B grating spectrometer as tflfixl films or CHCl3 solutions
using polystyrene (l601cm-1) calibration. The mass spectra
were run on a Hitachi-Perkin-Elmer RMU-6 mass spectrometer.
Ultraviolet spectra were measured on either a Unicam SP-800
or a Carey 14 spectrophotometer. The crystal structure on
trans-CDMBC was performed by Dr. D. Ward on a Picker FACS-I
automatic X-ray diffractometer. Phosphorescence spectra
were obtained on a Perkin-Elmer MPF-44A Fluorescence spec-
trometer connected to a Perkin-Elmer Differential Corrected

Spectra Unit.

144

.maumo cfi omzooimcmuu mo Esnuommm U

253 a

ma

.mH musmwm

 

 

 

 

 

145

.m

 

 

 

 

 

 

 

 

 

 

 

 

Homo ca umzomimcmuu mo Eouuommw UmH .ma wudmem
AEmmvm
j 3 xii—01714144144114 ((1 (1i (4 4 («(111 1 11:1;
moon. «.mma o.mom
0.: RS.
m.m~

v.mm
m.oma
m.n~a

~.mm 23. meme

 

 

146

.m

Homo se umzomimao mo ssuuo0dm 6

remove

ma

.om musmflm

 

 

 

 

m.HN
N.vm

m.mm

 

 

 

v.0v

o.mm

MUCH

m.hNH

 

 

m.oma

m.hNH

h.mma _

H.mom

 

 

LIST OF REFERENCES

1.

10.
11.

12.

13.

14.
15.
16.

LIST OF REFERENCES

G. G. W. Norrish and M. E. S. Appleyard, J. Chem. Soc.,
874 (1947).

 

N. C. Yang and D. H. Yang, J. Am. Chem. Soc., _2,
6672 (1970).

 

P. J. Wagner, P. A. Kelso, and R. G. Zepp, ibid., 22,
7480 (1972).

(a) R. D. Rauh and P. A. Leermakers, ibid., 22, 2246
(1968).

(b) F. D. Lewis, ibid., 22, 5602 (1970).
P. J. Wagner and R. G. ZepPr ibid., 22, 287 (1972).

M. A. El-Sayed, Accounts Chem. Res., 2, 8 (1968).

 

P. J. Wagner and G. S. Hammond, J. Am. Chem. Soc., 22,
1245 (1966).

 

P. J. Wagner, ibid., 89, 5898 (1967).

 

C. Walling and M. J. Gibian, ibid., 21, 3361 (1965).

P. J. Wagner, Accounts Chem. Res., 2, 168 (1971).

 

F. D. Lewis and T. H. Hillard, J. Am. Chem. Soc., _2,
6672 (1970).

 

P. J. Wagner and A. E. Kemppainen, ibid., 22, 5896
(1968).

P. J. Wagner, A. E. Kemppainen, and H. N. Schott, ibid.,
22, 5280 (1970).

F. D. Lewis and T. H. Hillard, ibid., 22, 6672 (1970).

P. J. Wagner and M. J. Thomas, ibid., 98, 241 (1976).

 

R. S. Mulliken, ibid., 22, 811 (1952).

147

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.
27.

28.
29.
30.
31.

32.

33.
34.

35.

36.

148

V. H. Leonhardt and A. Weller, Ber. Bunzenges.
Physick. Chem., 22, 791 (1973).

 

 

S. G. Cohen and A. D. Litt, Tetrahedron Letters, 579
(1965).

 

R. S. Davidson and P. F. Lambeth, Chem. Commun., 1265
(1967).

 

S. G. Cohen and H. M. Chao, J. Am. Chem. Soc., 22,
165 (1968).

 

S. G. Cohen and J. B. Guttenplan, Tetrahedron Letters,
5353 (1968).

 

P. J. Wagner and A. E. Kemppainen, J. Am. Chem. Soc.,
22, 3085 (1969).

 

S. G. Cohen and J. B. Guttenplan, J. Org. Chem., 22,
2001 (1973).

 

S. G. Cohen, A. Parola, and G. H. Parsons, Chem. Rev.,
22, 141 (1973).

 

S. G. Cohen and S. Ojanpera, J. Am. Chem. Soc., 22,
5633 (1975).

 

J. C. Scaiano, J. Photochem., 2, 81 (1973).

 

P. J. Wagner, A. E. Kemppainen, and T. Jellinek,;I.Am.
Chem. Soc., 22, 7512 (1972).

 

P. J. Wagner and D. A. Ersfeld, ibid., 22, 4515 (1976).
P. J. Wagner and B. J. Scheve, ibid., 22, 1858 (1977).
A. Padwa and A. Battisti, ibid., 22, 521 (1972).

K. Mislow, Rec. Chem. Prog., 22, 217 (1967).

 

G. S. Hammond and R. S. Cooke, J. Am. Chem. Soc., 22,
2958 (1968).

 

A. Padwa and R. Gruber, J. Org. Chem., _3£>_, 1781 (1970).

 

H. L. J. Backstrom and K. Sandros, Acta. Chem. Scand.,
22, 958 (1962).

 

P. J. Wagner and I. Kochevar, J. Am. Chem. Soc., _2,
2232 (1968).

 

P. J. Wagner, J. M. McGrath, and R. G. ZePP; ibid.,
22, 6883 (1972).

37.
38.

39.
40.
41.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.
53.
54.

55.

149

D. O. Cowan and A. A. Baum, ibid., 22, 1153 (1971).

P. J. Wagner, J. M. McGrath, and R. G. Zeppr ibid.,
24, 6883 (1972). _"

J. D. Coyle, Chem. Rev., 12, 97 (1978).

 

P. J. Wagner, Top. Curr. Chem., 22, 1 (1976).

 

F. D. Lewis and T. A. Hillard, J. Am. Chem. Soc., 22,
3852 (1972).

 

P. J. Wagner and R. G. Zepp, ibid., 22, 287 (1972).

J. A. Barltrop and J. D. Coyle, "Excited States in
Organic Chemistry," John Wiley and Sons, Inc., New
York, 1975, p. 180.

P. J. Wagner and J. McGrath, J. Am. Chem. Soc., 22,
3849 (1972).

 

H. G. Heine, Justus Liebigs Ann. Chem., 732, 165
(1970).

 

F. D. Lewis and J. G. Magyar, J. Org. Chem., 22, 3102
(1972).

 

F. D. Lewis and R. W. Johnson, J. Am. Chem. Soc., 22,
8915 (1972).

 

J. D. Coyle, Chem. Rev., 76, 97 (1978).

 

E. S. Huyser, "Free-Radical Chain Reactions," John
Wiley and Sons, Inc., New York, 1970, p. 211.

H. G. Heine, J. J. Rosenkronz, and H. Rudolph,
Angew. Chem. Intern. Ed. Eng., 22, 974 (1972).

 

G. A. Berchtold and W. C. Lumma, J. Org, Chem., 22,
1566 (1969).

 

J. R. Collier and J. Hill, Chem. Commun., 640 (1969).

S. Majeti, Tetrahedron Letters, 2323 (1971).

 

P. deMayo, C. L. McIntosh, and R. W. Yip, Tetrahedron
Letters, 37 (1967).

 

P. J. Wagner, "Creation and Detection of the Excited
State," Vol. 1A, A. A. Lamola, ed., Marcel Decker, New
York, 1971, p. 173.

56.

57.

58.

59.
60.

61.

62.

63.

64.

65.

66.

67.

68.

69.

70.

71.

72.

73.

74.

150

A. A. Lamola and G. S. Hammond, J. Chem. Phys., 22,
2129 (1965).

 

P. J. Wagner, 1. E. Kochevar, and A. E. Kemppainen,
J. Am. Chem. Soc., 22, 7489 (1972).

 

A. A. Lamola and G. S. Hammond, J. Chem. Phys., 22,
2129 (1965).

 

P. J. Wagner, Accounts Chem. Res., 2, 168 (1971).

 

P. J. Wagner and R. G. Zepp, J. Am. Chem. Soc., 22,
4958 (1971).

 

P. J. Wagner, P. A. Kelso, A. E. Kemppainen, and R. G.
Zeppr ibid., 22, 7500 (1972).

S. an (editor), "Organic Chemistry of Sulfur,"
Plenum Press, New York, 1977, pp. 249, 393, and 528.

P. J. Wagner, Tetrahedron Letters, 1753 (1967).

 

P. J. Wagner, P. A. Kelso, A. E. Kemppainen, J. M.
McGrath, H. N. Schott, and R. G. Zepp, J. Am. Chem.
Soc., 22, 7506 (1972).

 

A. Padwa and D. Pashayan, J. Org. Chem., 22, 3550
(1971).

 

F. D. Lewis and N. J. Turro, J. Am. Chem. Soc., 22,
311 (1970).

 

M. C. Caserio, W. Lauer, and T. Novinson, ibid., 22,
6082 (1970).

P. J. Wagner and A. E. Kemppainen, ibid., 22, 7495
(1972).

C. Walling and M. J. Mintz, ibid., 89, 1515 (1967).

 

A. Ohno, Y. Ohnishi, and N. Kito, Int. J. Sulfur
Chem., 2, 153 (1971).

 

E. S. Huyser, "Free-Radical Chain Reactions," John
Wiley and Sons, New York, 1970, p. 235.

J. K. Kochi and P. J. Krusic, J. Am. Chem. Soc., 22,
3940 (1969).

 

P. J. Wagner and A. E. Kemppainen, ibid., 22, 7495
(1972). -—-—-

F. D. Lewis andN.J.Turro, ibid., a, 311 (1970).

75.

76.

77.

78.

79.

80.

81.
82.

83.

84.

85.

86.

87.

88.

89.

90.

91.
92.

151
P. J. Wagner and A. E. Kemppainen, ibid., 22, 7495
(1972).

P. J. Wagner and A. E. Kemppainen, ibid., 22, 7495
(1972).

P. J. Wagner and J. H. Sedon, Tetrahedron Letters,
1927 (1978).

 

E. S. Huyser and R. H. C. Feng, J. Org. Chem., _2,
731 (1971).

 

P. B. Shevlin, T. E. Boothe, J. L. Greene, M. R.
Willcoth, R. R. Inners, and A. Cornelis, J. Am. Chem.
Soc., 100, 3874 (1978).

 

 

(a) J. R. Collier and J. Hill, Chem. Commun., 700
(1968).

 

(b) P. deMayo, C. L. McIntosh, and R. W. Yip, Tetra-
hedron Letters, 37 (1967).

 

F. D. Lewis, private communication.

P. J. Wagner and J. M. McGrath, J. Am. Chem. Soc.,
22, 3849 (1972).

 

F. D. Lewis, C. H. Hoyle, and J. G. Magyar, J. Org.
Chem., 22, 488 (1975).

F. D. Lewis, R. T. Lanterback, H. G. Heine, W. Hart-
mann, and H. Rudolph, J. Am. Chem. Soc., 22, 1519
(1975).

 

S. Majeti, Tetrahedron Letters, 2523 (1971).

 

P. deMayo, C. L. McIntosh, and R. W. Yip, ibid., 22,
(1967).

M. A. El-Sayed, Accounts Chem. Res., 2, 8 (1968).

 

B. J. Scheve, Ph.D. Thesis, Michigan State University,
1974.

P. J. Wagner and A. E. Kemppainen, J. Am. Chem. Soc.,
22, 7495 (1972).

 

P. J. Wagner and A. E. Kemppainen, ibid., 22, 7495
(1972). t

W. B. Mueller, unpublished results.

P. J. Wagner and B. J. Scheve, J. Am. Chem. Soc., 22,
1858 (1977).

 

93.

94.

95.

96.

97.

98.

99.

100.

101.

102.

103.

104.

105.

106.

107.

108.
109.

152
P. J. Wagner and A. E. Kemppainen, ibid., 22, 3085
(1969).
P. J. Wagner and D. A. Ersfeld, ibid., 22, 4515 (1976).

A. Padwa and D. Pashayan, J. Org. Chem., 22, 3550
(1971).

 

A. H. Weller and H. Leonhard, Ber. Bunsenges. Phys.
Chem., 21, 791 (1963).

 

S. G. Cohen and J. B. Guttenplan, Chem. Commun., 247,
(1969).

 

S. G. Cohen and J. B. Guttenplan, J. Org. Chem., 22,
2001 (1973).

 

C. R. Johnson, H. Diefenbach, J. E. Kaiser, and J. C.
Sharp, Tetrahedron, 22, 5649 (1969).

 

N. Kharasch (editor), "Organic Sulfur Compounds,"
Vol I, Pergammon Press, New York, 1961, pp. 47-74.

A. J. Gordon and R. A. Ford, "Chemist's Companion,"
Wiley-Interscience, New York, 1972, p. 238.

H. H. Jaffe and M. Orchin, "Theory and Application of
Ultraviolet Spectroscopy," John Wiley and Sons, New
York, 1962.

S. G. Cohen and J. B. Guttenplan, Chem. Commun., 247
(1969).

 

S. G. Cohen and J. B. Guttenplan, J. Org. Chem., 22,
2001 (1973).

 

(a) E. L. Eliel, "Steric Effects in Organic Chemistry,"
M. S. Newman, ed., John Wiley and Sons, New York,
1956, pp. 114-120.

(b) E. L. Eliel, "Stereochemistry of Carbon Compounds,"
McGraw Hill, New York, 1962, pp. 198-202.

J. E. Gano and L. Eizenberg, J. Am. Chem. Soc., 22,
974 (1973).

 

F. D. Lewis and T. A. Hilliard, J. Am. Chem. Soc.,
22, 6672 (1970).

 

P. J. Wagner and M. J. Thomas, ibid., 8, 241 (1976).

 

G. S. Hammond and P. A. Leermakers, ibid., 22, 207
(1962).

153

110. P. J. Wagner and D. A. Ersfeld, ibid., 22, 4515 (1976).

111. S. Majeti, Tetrahedron Letters, 2523 (1971).

 

112. P. J. Wagner, A. E. Kemppainen, and H. N. Schott,
J. Am. Chem. Soc., 22, 5604 (1973).

 

.113. J. A. Barltrop and A. J. Thomson, J. Chem. Soc. (C),
155 (1968).

114. K. Schaffner and S. Iwasaki, Helv. Chim, Acta., 22,
557 (1968).

 

115. P. S. Skell and P. D. Readio, J. Am. Chem. Soc., 22,
3334 (1964).

 

116. G. Karabatsos in "Topics in Stereochemistry," E. L.
Eliel and N. L. Allinger, eds., Vol V, 1970, pp. 167-
203.

117. G. Karabatsos and O. J. Fenoglio, J. Am. Chem. Soc.,
22, 3577 (1969).

 

118. N. L. Allinger, J. Allinger, L. A. Freiberg, R. F.
Czaja, and N. A. LeBei, J. Am. Chem. Soc., 22, 5876
(1960).

 

119. K. Schaffner and S. Iwasaki, Helv. Chim, Acta.,22,
557 (1968).

 

120. J. Bitha and J. Hlavka, Tetrahedron Letters, 3843
(1966).

 

121. J. Schriesheim, Chem. Ind., (London), 1234 (1963).

 

 

 

 

122. P. G. Russel, J. Phys. Chem., 22, 1350 (1975).

123. S. Majeti, Tetrahedron Letters, 2523 (1971).

124. P. J. Carlson and K. U. Ingold, J. Am. Chem. Soc.,
22, 1055 (1968).

125. S. Huyser and J. D. Taliaferro, J. Org. Chem.,

 

NM

8, 3442 (1963).

126. R. A. Sheldon and J. K. Kochi, J. Am. Chem. Soc.,
22, 4392 (1970).

 

127. J. Calvert and J. Kraus, ibid., 12, 5921 (1957).

128. P. D. Bartlett and S. F. Nelson, ibid., 22, 135
(1966).

154

129. D. R. Kearns and W. A. Case, ibid., 22, 5087 (1966).

130. P. J. Wagner, A. E. Kemppainen, and H. N. Schott,
ibid., 22, 5604 (1973).

131. P. J. Wagner, A. E. Kemppainen, and H. N. Schott,
ibid., 22, 5604 (1973).

132. Y. H. Li and E. C. Lim, Chem. Phys, Lett., 2,
15 (1970).

 

133. P. J. Wagner,bL.May, and A. Haug, ibid., 22, 545
(1972). ‘_—"

134. P. J. Wagner, M. May, and A. Haug, ibid., 22, 545
(1972).

 

135. R. Castonguay and A. C. Albrecht, ibid., 2, 89
(1970).

136. E. J. Corey, J. Am. Chem. Soc., 75, 2301 (1953).

 

137. R. N. Jones, D. A. Ramsey, F. Herling, and K. Dobriner,
ibid., 12, 2828 (1952).

138. N. L. Allinger, J. C. Tai, and M. A. Miller, ibid.,
22, 4495 (1966).

139. R. Hoffmann, C. C. Levin, W. J. Hehre, and J. Hudec,
J. Chem. Soc., Perkin II, 210 (1973).

 

140. J. N. Murrell, "The Theory of the Electronic Spectra
of Organic Molecules," John Wiley and Sons, New York,
1963, pp. 164-168.

141. J. Labhart and G. Wagniere, Helv. Chim. Acta, 22,
2219 (1959).

 

142. R. F. Whitlock and A. B. F. Duncan, J. Chem. Phys.,
22, 218 (1971).

 

143. R. C. Cookson, J. Henstock, J. Hudec. J. Am. Chem.
Soc., 22, 1061 (1966).

 

144. W. D. Chandler and L. Goodman, J. Mol. §pec.,22, 232
(1970).

 

145. P. J. Wagner, A. E. Kemppainen, and H. N. Schott,
J. Am. Chem. Soc., 22, 5604 (1973).

 

146. P. J. Wagner and A. E. Kemppainen, ibid., 22, 5898
(1968).

 

147.
148.

149.

150.

151.

152}
153.

154.
155.

156.

157.

158.

159.
160.

161.

162.

163.

155

P. J. Wagner, Accounts Chem. Res., 2, 168 (1971).

 

G. A. Berchtold and W. C. Lumma,
1566 (1969).

J. Org. Chem., 22,

 

C. Walling,
and Sons, New York, 1957, pp.

"Free Radicals in Solution," John Wiley
467-563.

C. Walling and P. S. Fredricks, J. Am. Chem. Soc.,
22, 3326 (1962).

 

M. Szwarc and D. Williams, J. Chem. 1171

(1952).

Phys., 39.

K. Griesbaum, Angew. Chem. Int. Ed., 2, 273 (1970).

 

J. L. Rice in "Free Radicals," J. K. Kochi, ed.,
Wiley Interscience, New York, Vol. II, p. 809.

s. w. Benson, Chem. Rev., lg, 23 (1978).

 

E. L. Eliel,
McGraw-Hill,

"Stereochemistry of Carbon Compounds,"
Inc., 1962, p. 236.

D. J. Pasto and C. R. Johnson,
Determination," Prentice-Hall,
Cliffs, 1969, p. 169.

"Organic Structure
Inc., Englewood

R. M. Silverstein, G. C. Bassler, and T. C. Morrill,
"Spectrometric Identification of Organic Compounds,"
John Wiley and Sons, Inc., New York, 1974, p. 168.

F. D.
Chem.

Lewis, R. W. Johnson, and D. E. Johnson,.J.Am.
Soc., 22, 6090 (1974).

 

F. D. ibid., 94,

Lewis and R. W. Johnson, 8915(1972).

 

P. J. Wagner and J. H. Sedon, Tetrahedron Letters,
1927 (1978).

 

F. D. Lewis, R. W. Johnson, and D. E. Johnson,.J.Am.
Chem. Soc., 22, 6090 (1974).

 

P. J. Wagner and J. H. Sedon, Tetrahedron Letters,
1927 (1978).

 

(a) R. Eckling, P. Goldfinger, G. Huybrechts, G.
Martens, L. Meyers, and S. Smoes, Chem. Ber.,
22, 3014 (1960).

 

(b) P. B. Ayscough, A. J. Cocker, F. S. Dainton, S.
Hirst, and M. Weston, Proc. Chem. Soc. London,
244 (1961).

 

164.

165.

166.

167.

168.

169.

170.
171.

172.

173.

174.

175.

176.

177.

178.

179.

180.

156

N. S. Isaacs, “Reactive Intermediates in Organic
Chemistry," John Wiley and Sons, New York, 1974,
p. 105.

H. C. Brown and Y. Okamoto, J. Am. Chem. Soc., 22,
1913 (1957).

 

(a) A. A. Lamola, J. Chem. Phys., _4_7_, 4810 (1967).

 

(b) R. D. Rauh and P. A. Leermakers, J. Am. Chem.
Soc., 22, 2246 (1968).

 

R. D. Small and J. C. Scarano, Chem. Phys. Lett.,
22, 431 (1977).

 

P. J. Wagner, J. H. Sedon, and M. J. Lindstrom,
J. Am. Chem. Soc., 100, 2579 (1978).

 

H. E. O'Neal, R. G. Miller, and E. Gunderson, ibid.,
'2_, 3351 (1974).

H. C. Brown and G. Wheeler, ibid., 12, 2199 (1956).

K. Griesbaum, Angew. Chem. Int. Ed., 2, 273 (1970).

 

E. S. Huyser, "Free-Radical Chain Reactions," Wiley-
Interscience, New York, 1970, p. 229.

J. L. Kice in "Free Radicals," J. K. Kochi, ed.,
Wiley-Interscience, New York, Vol. II, p. 715.

E. Block, Quart. Reports on Sulfur Chem., 2, 315
(1969).

 

G. A. Russell and J. Lokensgard, J. Am. Chem. Soc.,
22, 5059 (1967).

 

P. B. Ayscough, A. J. Cocker, F. S. Dainton, S.
Hirst, and M. Weston, Proc. Chem. Soc. London, 244
(1961).

 

D. N. Hall, J. Org. Chem., 2, 2082 (1967).

 

R. D. Small and J. C. Scaiano, Chem. Phys. Lett.,
22, 431 (1977).

 

P. J. Wagner and J. H. Sedon, Tetrahedron Letters,
1927 (1978).

P. J. Wagner and J. H. Sedon, ibid., 1927 (1978).

181.

182.

183.

184.
185.

186.

187.
188.
189.

190.

191.

192.
193.

157

P. S. Skell and K. J. Shea in "Free Radicals,"
J. K. Kochi, ed., Wiley-Interscience, New York,
Vol. II, p. 809.

P. B. Shevlin, T. E. Booth, J. L. Greene, M. R.
Willcott, R. R. Inners, and A. Cornelis, J. Am. Chem.
Soc., 100, 3874 (1978).

 

C. Walling and M. J. Gibian, J. Am. Chem. Soc., 21,
3361 (1965).

 

P. S. Skell and P. D. Readio, ibid., 86, 3334 (1964).

 

L. P. Hammet, "Physical Organic Chemistry," McGraw-
Hill, Inc., New York, 1970, p. 384.

P. S. Skell, P. D. Readio, R. Tuleen, J. Am. Chem.
Soc., 22, 2615 (1966).

P. S. Skell and P. D. Readio, ibid., 86, 3334 (1964).

 

F. D. Lewis and R. S. Johnson, ibid., 22, 8915 (1972).

 

F. D. Lewis, R. W. Johnson, and D. E. Johnson, ibid.,
96, 6090 (1974).

E. J. Corey and M. Chaykovsky, ibid., 22, 1345
(1965).

B. J. Scheve, Ph.D. Thesis, Michigan State University,
1974.

S. Majeti, Tetrahedron Letters, 2523 (1971).

 

P. J. Wagner, I. E. Kochevar, and A. E. Kemppainen,
J. Am. Chem. Soc., 22, 7489 (1972).

 

APPENDIX

APPENDIX

This section contains the raw experimental data,
such as product to standard ratios, internal standard
concentrations, etc., used to calculate the various
photokinetic parameters.

The data is arranged in tabular form as follows:
the concentration of internal standard for the actinometry
is listed first. C16 was used exclusively for all valero-
phenone actinometry. The correction factor for acetophenone
versus C16 is 2.3. Other correction factors are listed (in
parentheses) after the concentration of standard to which
it refers. The quencher that was used for the Stern-Volmer
plot is listed next, followed by the column and column
conditions. The description of the various columns are
listed in the Experimental section.

Quenching data, including quencher concentrations,
product to standard ratios, and ¢°/¢ values, are listed next.
The concentrations of internal standards for the quenching

3 to lo'ZM.

runs were not measured but were in the range 10-
The values immediately below the quenching data are
the prod/std ratios used for calculating the respective

quantum yields. In most cases the concentration of standard

in all tubes is the same as the actinometer. In some cases

158

159

different concentrations of standard were used for each tube.
In these cases the prod/std ratios are listed in the same
order as previously listed concentrations.

Abbreviations used in this section are: Pip =
piperylene; l-NM = l-methylnapthalene; Napth = napthalene;
act = actinometer (valerophenone in all cases); acet =
acetophenone; Bzald = benzaldehyde; DMBC = 1,4-dimethyl-l-
benzoylcyclohexane; 4-BB = 4-benzoyl-l-butene; and pyr =
pyridine. All quantum yields were performed at 3130A.
Quenching runs utilizing piperylene were performed at
31303. Quenching runs utilizing napthalene or l-methyl-
napthalene were performed at 3660A. Photolysis times were
usually between one and three hours. The intensity of the

lamp varied between 0.005 and 0.01 Einsteins M71.

160

Table 22. Data for 2-Thiomethylacetophenone.

0.0140M C16, 0.0154M C16, 0.0139M C16
Pip quencher
Col #1 145°C

 

 

 

 

 

 

 

[Q] ' prod/std ¢°/¢
0.00 2.38 --
0.24 1.40 1.70
0.55 0.96 2.30
1.26 0.66 3.60
1.53 0.59 4.10
act 0.158
acet 0.122
acet(0.05M PhSH) 0.169
Table 23. Data for Thio-t-butylacetophenone.

0.0139M C16

l-MN quencher

Col #1 145°C

[0] prod/std ¢°/¢
0.00 0.88 --
0.08 0.68 1.29
0.16 0.53 1.66
0.50 0.29 3.00
act 0.140

acet(0.05M PhSH)

0.017

 

161

Table 24. Data for 2-Thiobutylacetophenone.

0.025M C16
l-MN quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢
0.0 0.49 --
0.3 0.29 1.67
0.7 0.24 2.00
1.0 0.19 2.50
act 1.82
acet 2.37

acet(0.05M PhSH) 2.84

 

Table 25. Data for 4-Thiobutylbutyrophenone.

0.011M C16
Pip quencher
Col #1 145°C

 

 

 

acet(l.0M dioxane)

[Q] prod/std ¢°/¢
0.0 0.20 --
0.3 0.13 1.5
0.6 0.10 1.9
1.0 0.08 2.6
act 0.27

acet 0.08

0.15

 

162

Table 26. Data for 4-Thio-t—butylbutyrophenone.

0.014M C16
Pip quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢
0.0 0.29 --
0.4 0.16 1.8
0.8 0.09 2.9
1.2 0.07 3.6
act 0.49

acet 0.39

 

Table 27. Data for 4-Thiophenylbutyrophenone.

0.005M C16
Pip quencher
Col #1 145°C

 

 

 

acet(l.0M dioxane)

[Q] prod/std ¢°/¢
0.0 0.37 --
0.3 0.16 2.4
0.6 0.09 3.9
1.0 0.06 5.9
act 0.52

acet 0.50

0.57

 

163

Table 28. Data for 5—Thiobutylvalerophenone.

0.006M C12 (1.63)
Pip quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢

0.00 0.72 --

0.02 0.44 1.6

0.06 0.22 3.3

0.10 0.16 4.5
act 0.330
acet(l.0M dioxane) 0.210
4-BB(l.0M dioxane) 0.003

 

Table 29. Data for 5-Thiophenylvalerophenone.

0.011M C16 (1.67)
Pip quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢

0.00 0.72 --

0.02 0.44 1.6

0.06 0.22 3.3

0.10 0.16 4.5
act 0.615
acet(l.0M dioxane) 0.029
4-BB(l.0M dioxane) 0.840

 

.—

164

Table 30. Data for 6-Thicbuty1hexanophenone.

0.026M C16
Pip quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢

0.00 0.32 --

0.02 0.20 1.6

0.06 0.09 3.3

0.10 0.06 5.2
act 0.16
acet 0.10
acet(1.0M dioxane) 0.12

 

Table 31. Data for 5-Thiocyanatovalerophenone.

0.041M C16 (1.67)
Pip quencher
C01 #1 145°C

 

 

 

[Q] prod/std ¢°/¢
0.0 2.0 --
0.2 0.64 3.10
0.4 0.39 5.10
0.6 0.17 11.0
act 1.38

acet(l.0M dioxane) 0.02

4-BB(1.0M dioxane) 1.27

 

165

 

 

 

 

Table 32. Data for 5-Thioacetoxyva1erophencne.
0.0548M C16 (1.67)
Pip quencher
Col #1 145°C
[Q] prod/std ¢°/¢
0.00 1.61 --
0.06 0.42 3.8
0.12 0.26 6.0
act 0.370
acet 0.023
acet(1.0M pyridene) 0.870
4-BB 0.648
Table 33. Data for 2-Methy1sulfinylacetophenone.

0.025M C16
1-MN quencher
Col #1 145°C

 

 

 

acet(0.05M PhSH)

[Q] prod/std ¢°/¢
0.0 1.58 --
0.5 1.06 1.48
1.0 0.80 1.97
act 1.13
acet 0.37

1.49

 

166

Table 34. Data for 4-Buty1sulfinylbutyrophenone.

0.011M C16
Pip quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢

0.00 0.52 --

0.02 0.41 1.28

0.04 0.29 1.78

0.06 0.27 1.89

0.08 0.23 2.27
act 0.516
acet 0.048
acet(1.0M dioxane) 0.052

 

Table 35. Data for 5-Buty1sulfinylvalerophenone.

0.0088M C16 (1.67)
Pip quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢

0.00 0.78 --

0.02 0.52 1.5

0.04 0.41 1.9

0.06 0.35 2.3

0.08 0.29 2.7
act ' 0.56
acet(1.0M dioxane) 0.05
4—BB(1.0M dioxane) 0.92

 

167

Table 36. Data for 2-Butylsu1fcnylacetophenone.

0.021M C16
l-MN quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢

0.000 0.63 --

0.012 0.19 3.2

0.016 0.14 4.6

0.020 - 0.11 5.7
act 1.78
acet 1.05
acet(0.05M PhSH) 0.28

 

Table 37. Data for S-Butylsulfonylbutyrophenone.

0.0075M C16
Pip quencher
C01 #1 145°C

 

 

 

[Q] prod/std ¢°/¢
0.0000 1.75 --
0.0004 0.746 2.3
0.0008 0.481 3.6
0.0010 0.300 5.8
act 0.932
acet 0.566
acet(1.0M dioxane) 0.263

 

 

168

Table 38. Data for 5-Butylsu1fony1va1erophenone.

0.0085M C16 (1.67)
Pip quencher
Col #1 145°C

 

 

 

 

 

 

 

[Q] prod/std ¢°/¢
0.000 1.36 --
0.002 1.10 1.24
0.004 0.75 1.81
0.006 0.61 2.23
act 0.66
acet(l.0M dioxane) 0.78
4-BB(1.0M dioxane) 0.07
Table 39. Data for 2-Thiopheny1acetophenone.
0.016M C16
1-MN quencher
Col #1 145°C
[Q] prod/std ¢°/¢
0.0 0.53 --
2.0 0.51 1.0
act 0.220
acet 0.051

acet(0.05M PhSH) 0.162

 

169

 

 

 

 

Table 40. Data for 2-Thiophenyl-4'-F1uoroacetophenone.
0.012M C16(2.3)
1-MN quencher
Col #1 145°C
[Q] prod/std ¢°/¢
0.0 0.6 --
2.0 0.6 1.0
act 0.45
acet . 0.063

acet(0.05M PhSH) 0.312
Table 41. Data for Thiophenyl-4'-ch10rcacetophenone.

0.012M C14, 01014M C14 (2.0)
Napth quencher
Col #1 145°C

 

 

 

acet(0.05M PhSH)

[Q] prod/std ¢°/¢
0.00 0.52 --
0.44 0.38 1.36
0.86 0.32 1.61
1.76 0.21 2.41
act 0.450
acet 0.075

0.344

 

170

Table 42. Data for 2-Thiopheny1-4'-bromoacetophenone.

0.012M C16, 0.0136M C16 (2.0)
Napth quencher
Col #1 145°C

 

 

 

 

[Q] prod/std ¢°/¢'
0.00 1.01 --
0.56 0.51 1.78
0.96 0.39 2.61
1.45 0.27 3.70
act 0.450
acet 0.085
acet(0.05M PhSH) 0.265

 

Table 43. Data for 2-Thiopheny1-4'-methy1acetophenone.

0.012M C16, 0.013M C14 (1.8)
Napth quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢
0.0 0.32 --
2.0 0.31 1.0
act 0.45
acet 0.078

acet(0.05M PhSH) 0.462

 

171

Table 44. Data for 2-Thiopheny1-4'-methoxyacetophenone.

0.0026M C16 (2.04)
Napth quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢
\ 0.00 0.39 --
0.48 0.20 1.97
0.98 0.12 3.36
act 0.263
acet 0.078
acet(0.05M PhSH) 0.367

 

Table 45. Data for 2-Thiopheny1-4 '-thiomethoxyacetophenone.

0.011M C16, 0.007M C19 (2.09)
Napth quencher
Col #1 170°C

 

 

 

[Q] prod/std ¢°/¢
0.000 0.57 --
0.007 0.38 1.48
0.040 0.24 2.32
0.090 0.15 3.68

act 0.39
acet 0.09

acet(0.05M PhSH)

0.42

 

172

Table 46. Data for 2-Thiopheny1-4'-dimethylaminoacetophenone.

0.011M C16, 0.002M C20 (2.37)
Napth quencher
C01 #1 190°C

 

 

 

[Q] prod/std ¢°/¢

0.00 1.68 --

0.04 1.21 1.34

0.06 0.900 1.87

0.10 0.600 2.80
act 0.210
acet 0.267
acet(0.05M PhSH) 0.443

 

Table 47. Data for 2-Thiopheny1-4'-pheny1acetophenone.

0.016M C16, 0.005M C20 (2.3)
Napth quencher
Col #1 190°C

 

 

 

acet(0.05M PhSH)

[Q] Prod/std ¢°/¢
0.000 4.43 --
0.008 2.99 1.48
0.015 2.57 1.72
0.026 2.17 2.00

act 0.630
acet 0.270

1.670

 

173

Table 48. Data for 2-Thiopheny1-4'-cyanoacetophenone.

0.0126M C16,0.0020M C19 (1.72)
Napth quencher
Col #1 190°C

 

 

 

[Q] prod/std ¢°/¢

0.00 0.44 --

0.16 0.34 1.29

0.56 0.29 1.52

0.96 0.22 2.00
act 0.31
acet 0.25
acet(0.05M PhSH) 1.14

 

Table 49. Data for 2-Thiophenylpropriophenone.

0.027M C16 (2.04)
Napth quengher
C01 #1 145 C

 

 

 

[Q] prod/std ¢°/¢
0.0 0.61 --
2.0 0.60 1.0
act 0.580
acet 0.256

acet(0.05M PhSH) 0.637

 

174

Table 50. Data for 2-Thiophenylisobutyrophenone.

0.0026M C16 (1.84)
Napth quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢
0.0 0.24 --
2.0 0.25 1.0
act 0.49
acet 0.67

acet(0.05M PhSH) 0.69

 

Table 51. Data for 1-Thiophenyl-1-benzoy1cyclopr0pane.

0.013M C16, 0.015M C15 (1.89), 0.014M C15(1d89)
Pip quencher
Col #1 145°C

 

 

 

[Q] ' prod/std ¢°/¢
0.00 0.77 --
1.12 0.33 2.33
1.65 0.20 3.61
act 0.274
acet 0.119

acet(0.05M PhSH) 0.382

 

175

Table 52. Data for 4'-Thiopheny1methylacetophenone.

0.0136M C16, 0.0070M C18 (2.3), 0.0063MC18 (2.3)
Napth quencher
Col #1 145°C

 

 

 

[Q] prod/std ¢°/¢
0.0 0.19 --
2.0 0.17 1.0
act 0.29
acet 0.19

acet(0.05M PhSH) 0.77

 

Table 53. Data for 4'-Thiopheny1acetophenone.

0.012SM C16, 0.0137M C16
C01 #1 145°C

 

 

prod/std

 

act 0.64

acet(0.05M PhSH) 0.001

 

176

Table 54. Data for Phenyldesylsulfide.

0.0126M C16, 0.0090MC20 (1.5) , 0.0100MC20 (1.5)
Col #1 190°C

 

 

 

prod/std
act 0.14
acet 0.0018
acet(0.05M PhSH) 0.0144

 

Table 55. Data for 5-Pheny1sulfinylvalerophenone.

0.0028M C16 (1.67)
C01 #1 145°C

 

 

 

prod/std

act 1.66

acet 0.009
acet(1.0M dioxane) 0.010
4-BB 1.770

4-BB(1.0M dioxane) 1.730

 

177

Table 56. Data for S-Phenylsulfonylvalerophenone.

0.0026M C16 (1.67)

Col #1 145°C

 

 

 

prod/std
act 1.27
acet 0.71
acet(1.0M dioxane) 0.59
4-BB 1.16
4-BB(1.0M dioxane) 1.16

 

Table 57. Solvent Effects on Quantum Yield for S-Chloro-

valerophenone.

0.00264M C16 (1.67)

0.10M pyr
Col #1 145°C

 

 

prod/std (acet)

prod/std (4-BB)

 

act
benzene
dioxane
acetonitrile
methanol

1.60
2.68
1.76
2.60
1.75

0.59
0.39
0.55
0.39

 

178

 

 

 

 

 

 

 

Table 58. Solvent Effects on Quantum Yield for 5-Chloro-
4'-methoxyva1erophenone.
0.025M C16 (1.67)
0.10M pyr
Col #1 145°C
acet/4-BB
acetonitrile 18
methanol 22
Table 59. Solvent Effects on Quantum Yield for 5-Chloro-
4'-trifluoromethylvalerophenone.
0.00242M C16 (2.04)
0.10M pyr
Col #1 145°C
prod/std (acet) prod/std (4-BB)
act 1.41 --
benzene 3.04 0.47
dioxane 0.99 0.18
acetonitrile 3.05 0.24
methanol 2.10 0.15

 

179

 

 

 

Table 60. Data for trans—4-Chloro-1,4-dimethy1-1—benzoy1-
cyclohexane.
0.0119M C16, 0.0024MC19 (1.56) , 0.0028MC14 (2.3)
Napth quencher, 0.05M pyr
Col #1 145°C
[Q] prod/std ¢°/¢
0.0 1.62a(0.16)b ---
0.002 1.28 (0.11) 1.27a(1.41)b
0.004 1.20 (0.08) 1.35 (2.06)
0.008 0.95 (0.06) 1.70 (2.78)
act 1.22
DMNC 3.97
Bzald 0.13
alcC 0.18

 

aRefers to DMBC.

b

Refers to benzaldehyde.

cRefers to the assumed bicyclic alcohol.

180

Table 61. Data for trans-4—Bromo-1,4-dimethy1-1—benzoy1-

cyclohexane.

0.0129M C16, 0.0134M C14 (2.3)
Napth quengher
Col #1 145 C

 

 

 

[Q] prod/std ¢°/¢
o.ooa(o.00)b 0.265(0.52) ---
0.004(0.02) 0.145(0.60) l.83(1.17)
0.008(0.04) ’ 0.100(0.78) 2.65(1.53)

-- (0.08) -- (0.92) -- (1.80)

act 0.442

Bza1d(0.05M pyr) 0.025
Bza1d(0.10M pyr) 0.026
DMBC(0.05M pyr)c A[pyr] = 0.016
DMBC(0.10M pyr)° A[pyr] = 0.018

 

aRefers to benzaldehyde.

bRefers to DMBC.

C
¢DMBC

determined by measuring the disappearance of pyridine .

181

Table 62. Data for cis-4-Bromo-1,4-dimethy1-1-benzoy1cyclo-
hexane.

0.0143M C16, 0.015M C14 (2.3)
Napth quencher
Col #4 145°C

 

 

 

[Q] prod/std ¢°/¢
0.000 0.050 (0.040) ---
0.010 0.030 (0.014) 1.70 (2.85)
0.017. 0.023 (0.001) 2.17 (4.80)
act 0.304
Bza1d(0.05M pyr) 0.092
DMBC (0.05M pyr) 0.110

 

Table 63. The 3-Thiobuty1propiophenone Sensitized Isomeri-
zation of cis-1,3-pentadiene.

Col #4 58°C

 

 

 

[t—P].M 0.55Mc+t
1.0(act) 0.0522 -_-
1.0 0.0278 1.98
1.5 0.0221 2.42
2.0 0.0203 2.64

2.5 0.0167 3.22

 

182

Table 64. The 4-Thiobutylbutyrophenone Sensitized Isomeri-
zation of cis-1,3-pentadiene.

 

 

 

Col #4 58°C
[c-pJ'l m‘l [t-P] M 0 55/¢
' ' ' c+t
1.0(act) 0.0673 --—
1.0 0.0429 1.57
1.5 0.0392 1.71
2.0 0.0329 2.04

 

Table 65. The 3-Butylsu1finylpropiophenone Sensitized
Isomerization of cis-1,3-pentadiene.

 

 

 

Col #4 58°C
[C-Pl'l 14'1 [t-P] M 0 55/¢
' ' ' c+t
1.0(act) 0.0652 ---
1.8 . 0.0296 2.20
5.0 0.0163 3.98

 

Table 66. The 3-Buty1sulfonylpropiophenone Sensitized
Isomerization of cis-1,3-pentadiene.

 

 

 

Col #4 58°C
[c-Pl-l M‘l [t-P] M 0 55/¢
' ' ’ c+t
2.0(act) 0.0068 ---
125.0 0.0040 1.71

83.0 0.0016 1.45