ABSTRACT EXCURSIONS INTO CHARGE AND ENERGY TRANSFER MECHANISMS: CONFORMATIONAL EFFECTS IN EXCITED STATES BY Bernard Joseph Scheve Part I Biphenyls Electron spin resonance (ESR) spectra of chloro- and methyl-substituted biphenyls. coupled with the measured efficiencies with which these biphenyls quench the phos- phorescence and photoreduction of benzophenone, indicate that two methyl groups located in the orthg, orthgf- positions of biphenyl are necessary to force triplet biphenyl from planarity. The electron spin resonance data indicate that two triplet species are produced from both 3,3' and 2,2'- dimethylbiphenyl. These are interpreted as corresponding with the z and E conformations. Only Z-2,2'—dimethyl- biphenyl can be deduced to be non-planar as evidenced by its higher D value than those of the other biphenyls. Decay rates of the triplet produced from the chloroderiva— tives during the ESR studies indicate that chlorine is being expelled. The data obtained from the Stern—Volmer analysis of the quenching of triplet benzophenone by the mono-substituted biphenyls suggest that orthg-substituents raise the triplet energy of biphenyl and that parafsubstituents lower the triplet energy of biphenyl. Methyl groups have less effect on the triplet energies than do chloro groups. These con- clusions are reinforced by absorption and phosphorescence spectra. Part II Azidoalkyl Phenyl Ketones The Type II photoelimination efficiencies were measured for y-,6-, and 5—, azidoalkyl phenyl ketones. Quenching of the excited state by an efficient triplet quencher allows kinetic analysis by the Stern-Volmer relationship. The rate data obtained for the 5- and 3- azidoketones were compared to a Hammett dp plot previously obtained with other substituents. The inductive substituent constant 01 of the azido group is calculated to be 0.46. The rate data for the y-azidoketones were quantitatively separated into inductive and radical stabilizing constituents, since 9 for the Y-carbon has been estimated to be -4.3. The Stern-Volmer treatment of the data also allows calculation of the rates of energy transfer from the carbonyl moiety to the azido moiety. The rate of this endothermic intramolecular energy transfer was found to be lower than that of exothermic intermolecular energy transfer. Part III Piperidyl Ketones A synthesis of N-substituted-4-methyl-4-benzoyl- piperidine is described. Irradiation of this Demerol—type compound produces 2-methyl-5-methyl-6-phenyl-2-aza-bicyclo £321.l_7hepta-6-ol (a member of the amphetamine family). The efficiencies with which the N-methyl derivative under- goes the Type I and Type II reactions were determined. Quenching studies indicate that the two reactions occur from two distinct triplets, presumably two different conformers. Their triplet lifetimes, determined by Stern- Volmer analysis, are compared to those of l-methylcyclohexyl phenyl ketone and y-dimethylaminobutyrophenone. The results indicate that there is no intramolecular charge-transfer quenching of the triplet carbonyl by the nitrogen lone pair in the piperidyl ketones.A Stern-Volmer quenching study of 1-methylcyclohexyl phenyl ketone by N-methylpiperidine indicates about a 50 fold decrease in the rate constant for intermolecular charge-transfer quenching relative to the quenching rate observed for diene quenching of the ketone. This suggests that there exists a large steric barrier to charge transfer quenching. EXCURSIONS INTO CHARGE AND ENERGY TRANSFER MECHANISMS: CONFORMATIONAL EFFECTS IN EXCITED STATES BY Bernard Joseph Scheve A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 1974 To Anne, Tim, and Company ii ACKNOWLEDGEMENTS The author wishes to thank both Dr. Peter J. Wagner and Dr. Charles A. Lundberg for reinforcing the author's concept of what qualities constitute a Ph.D. chemist. Their friendship, support, confidence, enthusiasm for chemistry, and overall good humor during the author's wanderings is greatly appreciated. It has been a pleasure to work with these knowledgeable colleagues. Support, both financial and spiritual, from the author's families and friends is greatly appreciated. Special thanks is given to the Chemistry Department at Michigan State University both for the various teaching assistantships and the general overall excellent facilities available for conducting good research. Thanks to the NSF for research asssitantships administered by Professor Wagner. Progress towards the Ph.D. would indeed have been a dreary task without the aid, advice, counsel, and discussions enjoyed with fellow graduate students. iii TABLE OF CONTENTS Page INTRODUCTION............. ......................... 1 Introductory Remarks...... .......... ......... 1 Objectives.... ..... . ......................... l Jablonski Diagram ............................ 3 Energy Transfer.... ....... . .................. 6 Hydrogen Atom Abstraction.. ..... . ............ 12 (a) Photoreduction of benzophenone ...... 12 (b) Type II reaction .............. . ..... 14 Type I Photocleavage ......................... 17 Charge Transfer....... ......... . ............. 18 (a) Intermolecular.. ..... .... ...... ..... 19 (b) Intramolecular....... ..... . ......... 21 Biphenyl..... ............... .. ............... 22 N-Substituted-4-Methyl-4-Benzoylpiperidine... 24 Azidoalkyl Phenyl Ketones .................... 27 The Azido Group.. ....... .... ..... . ........ ... 28 (a) The azide excited state............. 29 (b) Decomposition to nitrenes ........... 30 (c) Products from bichromOphoric Azidoalkyl phenyl ketones.. ......... 33 RESULTS (Part I).,,,, ......... .. .................. 35 Quenching of Triplet BenZOphenone by Biphenyls 35 iv TABLE OF CONTENTS (Continued) Page Absorption Spectra of Biphenyls.. .............. 37 Phosphorescence Spectra of Biphenyls.. ......... 37 Fluorescence Spectra of Biphenyls... ........... 50 Triplet EPR Spectra of Biphenyls..... ...... .... 50 DISCUSSION (Part I)............ ......... ... ......... 58 Planarity of Biphenyl Triplet.. ............. ... 58 Effects of Substituents on the Triplet.... ..... 60 Effect of mgta—Substituents.... ................ 61 Steric Effect of ortho-Substituents ............ 62 Effects of Substituents On Ground State Biphenyl ..... . .............. ... ....... . ........ 63 Distortion of Triplet as Evidenced by the Quenching Studies .............................. 66 Triplet Energy of Biphenyls.. .................. 66 Construction of Potential Energy Diagram ....... 67 RESULTS (Part II)............ ........... ...... ...... 71 Identification of Photoproducts of Azidoalkyl Pheny1KetoneSOOOOO0............OOOOOOOOOOOOOOO 71 (a) From y-Azidobutyrophenone.... ..... .... 71 (b) From 6-Azidovalerophenone ........ ..... 76 (c) From e-Azidohexanophenone ....... ...... 77 Quantum Yields.. ........................ ....... 77 Wavelength Effects.................... ..... .... 78 Variation of Quantum Yield with Per-cent Conversion.... ................................. 78 Concentration Effect ............ . .............. 81 Quenching Studies. ............................. 82 Intersystem Crossing Yields .................... 82 TABLE OF CONTENTS (Continued) Corrections applied to Quantum Yields and Quenching Studies....... ...... ........ ........... . Calculation of kr Values ........... . .............. Calculation of Rates of Energy Transfer........... DISCUSSION (Part II).... ............................... Mechanistic Scheme for Azidoalkyl Phenyl Ketones.. Mechanism for Formation of Photoproducts from y-Azidobutyrophenone.............................. Calculation of o and Stabilization Factor for the Azide Group...........OOOOOOOOOOOOOOOOOOO. Intramolecular Energy Transfer............ ........ Charge-Transfer Quenching by the Azide Group...... Indications for Further Research ......... ......... RESULTS (Part III). syntheSiSOOOOOOO......OOOOOOOOO ....... O ..... .00... Identification of PhotOproducts. .................. QuantuineldSOOOOOOOOOO ..... ......OOOOOOOOOOOOOOO (a) Type (b) Type I cleavage .......................... II elimination. O O O O O O ...... O ........ (c) Disappearance. ........................... Behavior in Presence of Quenchers ................. (a) Type (b) Type Sensitization Disappearance IOOOOOOOOOOIOOOOOOOOOOOO ....... 0.... studieSOOOOO0.000.000.0000. ......... of the Type II Photoproduct ......... NMR Studies on Ground State NMMBP ................. (a) Low temperature proton NMR ......... ...... 13 (b) C low temperature NMR ........... . ...... vi Page 83 88 89 93 93 94 96 100 103 104 106 106 108 109 109 110 110 111 111 114 117 119 120 120 120 TABLE OF CONTENTS (Continued) DISCUSSION (Part III) ................................. Ground State Conformations of NMMBP .............. Conformationally Interesting Compounds........... Intermolecular Energy Transfer Between Conformers Steric Effect to Intermolecular Charge-Transfer Quenching......... ...... . ........................ Sensitization Studies ............................ Disappearance of Type II Product. .......... . ..... Type I and Type II Quenching SlOpes......... ..... Partitioning of Energy in Excited NMMBP .......... Behavior in Polar Solvents ....................... (a) (b) Pyridine.....O... OOOOOOOOOOOOOOOOO O ..... Alcoholic Solvents.......... ............ Indications for Further Research................. EXPERIMENTAL (Part I) Preparation and Purification of Starting Materials........... Solvents........... ....... . ...................... (a) Benzene... .............................. (b) 2—Pr0panol, ............................ . (c) Cyclohexane, ..................... ....... (d) Pyridine.. .............................. (e) Methanol........................ ...... .. (f) Methylcyclohexane ......... .... ........ .. (g) Heptane.... ....................... . ..... (h) Ethanol... .............................. (i) Dodecanethiol........ ........... ........ (j) l-Propanol. ...................... . ...... vii Page 122 122 124 124 127 128 129 130 131 132 132 134 135 137 137 137 137 137 137 138 138 138 138 138 138 TABLE OF CONTENTS (Continued) Page (k) Acetonitrile ............................ I!“ Internal Standards ............................... 138 (a) Dodecane..... ........................... 138 (b) Tetradecane.. ........................... 138 (c) Hexadecane.. .............. . ............. 138 (d) Heptadecane ............................. 138 (e) Octadecane .............................. 139 (f) Nonadecane .............................. 139 (g) Decyl alcohol ........................... 139 Quenchers.......... ..... ... ..... ...... ........... 139 (a) Naphthalene...... ....... . ..... . ..... .... 139 (b) 1-Methylnaphthalene........ ...... ....... 139 (c) gig-piperylene ...................... .... 139 (d) Bipheny1.. ...................... . ....... 139 (e) 2-Chlorobipheny1 ........................ 139 (f) 3-Chlorobipheny1 ........................ 139 (g) 4-Chlorobiphenyl...... ...... . ........... 139 (h) 2-Methylbipheny1 .......... . ....... ...... 139 (i) 3-Methylbipheny1............. ....... .... 140 (j) 4-Methy1bipheny1 ........................ 140 (k) 2,2';3,3';4,4'-dimethylbiphenyl ......... 140 (l) Butyl azide. ............ ..... ........... 140 (m) 2-(Effluorophenyl)-Al-pyrroline ......... 140 (n) 2,5-Dimethy1-2,4-hexadiene .............. 141 (o) N-methylpiperidine ...................... 141 viii TABLE OF CONTENTS (Continued) Page Ketones. ........................................ 141 (a) Benzophenone ........................... 141 (b) Acetophenone ........................... 141 (c) Valerophenone ........................ .. 141 (d) Butyrophenone............. ......... .... 141 (e) pfAzidoacetophenone .................... 141 (f) y-Azidobutyrophenone......... .......... 142 (g) G-Azidovalerophenone ......... .......... 142 (h) e-Azidohexanophenone..... .............. 143 (i) 6-ThiocyanonatovalerOphenone........... 143 (j) N-methyl-4-methyl-4-benzoylpiperidine.. 143 (k) N-benzyl-4-methyl-4-benzoylpiperidine.. 146 (1) Rathke's base method... ..... ........... 148 (m) Phenyl-(N-methyl-4-methyl-4-piperidine- methanol..... ........... . ..... ......... 149 (n) l-methylcyclohexylphenyl ketone........ 149 Physical and Spectral Data for Synthesized Materials and Isolated Photoproducts ............ 150 Identification of Photoproducts............ ..... 156 (a) 2-methyl-5-methyl-6-pheny1-2- azabicyclo [3.1.3 hepta-6-ol ........... 156 (b) Photoproducts from y-Azidobuterphenone 157 EXPERIMENTAL (part II) Techniques .................... 159 Preparation of Samples ........... . .............. 159 (a) Disappearance of Benzophenone.. ..... ... 159 (b) Phosphorescence of Benzophenone ........ 159 (c) Azido and Amino Ketones................ 160 ix TABLE OF CONTENTS (Continued) Page (d) Sensitization Studies.. ................ 160 Degassing.... ................................... 160 Irradiation Procedure ............ . .............. 161 Ana1YSiS Of sampleSOIOO......OOOOCOIOOOOOOOOOOOO 162 (a) Disappearance of Benzophenone .......... 162 (b) Phosphorescence of Benzophenone........ 162 (c) Gas Chromatographic Procedures ......... 163 Actinometry. C O I O O OOOOOOOOOOOOOOOOOOOOOOOOOOOOO O O 164 (a) Valerophenone.......... ..... ........... 164 (b) Cis-piperylene-Acetophenone............ 167 SpectraOOOOOOOOOOOO......OOOOOOOOOOO......OOOOOO 168 EXPERIMENTAL (Part III) Experimental Data............ 191 Photoreduction and Emission Studies ............. 191 Gas Chromatographic Studies..... ....... ......... 201 LIST OF REFERENCESOIOOOOOOOOOOOOO ..... 00.00.000.000... 213 Table II. III. IV. v. VI. VII. VIa. VIIa. VIII. Ix. XI. XII. XIII. XIV. xv. LIST OF TABLES Page Quenching of Triplet BenZOphenone by Biphenyls in Benzene.......................... 38 Kinetic Parameters for Biphenyl Quenching of Triplet Benzophenone.......................... 39 Absorbance of Biphenyls.... ....... . .......... . 46 Phosphorescence of Biphenyls.. ............ .... 47 Fluorescence Data of Biphenyls................ 51 Observed EPR Resonances and ZFS Parameters of Phosphorescent Biphenyls...................... 54 Observed Angles of Twist and Van-der Waal's Radii for BiphenYloooooooooooooooooooooooooooo 64 GC/Mass Spectral Data for y-Azidobutyrophenone 72 GC/Mass Spectral Data for G-Azidovaler0phenone 76 Data for Azido Ketones Measured at 0.07 M Ketone Concentration Irradiated at 366 nm..... 91 Rate Data for Alkyl Azido Ketones in Benzene.. 92 Rates for Intramolecular Energy Transfer in Pheny1Ketones.....00.000.00.00.0....0.0.0.... 101 Type I Quantum Yields for 0.04 M Ketones at 313 nm........................................ 111 Type II Quantum Yields for 0.04 M Ketones at 313 anOOOOOOOO......OOOOOOOOOOOOOO00...... 112 Quenching Data for 0.04 M Ketones............. 113 Rate Data for Conformationally Interesting Ketones.....OOOOIOOOO ..... ......OOOOOOOOOOOOOOO 125 Spectral PrOperties of Synthesized and Isolated Materials........................ ..... 152 xi LIST OF TABLES (CONTINUED) Table Page XVI. Column Conditions Used to Determine PrOd/Std Ratios......OOOOOOOIOOOOOOOOOO.... 165 XVII. Standard/Product Ratios.................... 166 xii LIST OF SCHEMES Scheme Page I. Mechanism for Photoreduction of Benzophenone 10 II. Mechanism for Type II Reaction...... ........ 15 III. Behavior of y—Dimethylaminobuterphenone in Benzene.....I.0.0.0.0....0.00.00.00.00... 22 IV. Possible Products from Photolysis of Azido Ketones.....‘OOCOOOOOOO......OOOIOOOOOOOOOOO 34 V. The Behavior of y-Azidobuterphenone in Benzene.....OOOOOOOOIOO0............OOOOOOOO 97 VI. Possible Synthetic Routes for the Preparation of N-Methy1-4-methyl-4-benzoylpiperidine......107 VII. Behavior of N-methyl-4-methyl-4-benzoyl- piperidine in Benzene.........................133 xiii Figure II. III. IV. VI. VII. VIII. IX. XI. XII. XIII. XIV. LIST OF FIGURES Page Modified Jablonski Diagram ..................... 4 Photochemical Scheme for 1-methylcyclo- hexylphenyl Ketone ...... ....... ................ 26 w§+wx Transition in Alkyl Azides ............... 29 Stern-Volmer Plots for Quenching of Benzophenone Photoreduction by Biphenyl ........ 40 Stern-Volmer Plots for Quenching of Benzophenone Photoreduction by 4-Chlorobiphenyl. ..... .. ..... 40 Stern-Volmer Plots for Quenching of Benzophenone Phosphorescence by Biphenyl.. ..... ... ........... 41 Stern-Volmer Plots of Quenching of Benzophenone Phosphorescence by 4-Methy1bipheny1............ 41 Stern-Volmer Plots for Quenching of Benzophenone Photoreduction by 3-Chlorobiphenyl..... ....... . 42 Stern-Volmer Plots for Quenching of Benzophenone Phosphorescence by 2-Chlorobipheny1 ...... . ..... 42 Stern-Volmer Plots for Quenching of Benzophenone Photoreduction by 2-Chlorobiphenyl and Benzophenone Phosphorescence by 2-Methylbiphenyl 43 Plot of 1/8 Versus Ben20phenone Concentration (Phosphorescence) .......... ... ................. 44 Plot of l/S Versus Benzophenone Concentration (Photoreduction)... ............ . ......... . ..... 44 Phosphorescence Spectra of Biphenyl and Methyl- biphenyls. (———) Biphenyl, (---) 4-Methylbi- phenyl, (xxx) 2-Methy1biphenyl, (.--)3- Methylbiphenyl................................. 48 Phosphorescence Spectra of Biphenyl and Chloro- biphenyls. (———0 Biphenyl, (---) 2-Chloro- biphenyl, (xxx) 4-chlorobipheny1, (°") 3- Chlorobiphenyl.................. ............... 48 xiv LIST OF FIGURES (Continued) Figure XV. XVI. XVII. XVIII. XIX. XX. XXI O XXII. XXIII. XXIV. XXV. XXVI. XXVII. Page Phosphorescence (top) and Fluorescence (bottom) Spectra for Dimethylbiphenyls. (———)2,2'-Di- methylbiphenyl, (---) 3,3'-Dimethy1biphenyl, (xxx) Biphenyl, (---) 4,4'-Dimethy1bipheny1... 49 Am=2 Signals for 2,2'-Dimethylbiphenyl (solid line) and 3,3'-Dimethy1biphenyl (dotted line). Field Measured in Gauss........................ 56 Z-Signals for 2,2'-Dimethylbipheny1 (top) and 3,3'-Dimethylbipheny1 (bottom). Field measured in Gauss.... ......... . ....... ......... 56 X & Y Signals for 2,2‘-Dimethy1bipheny1 (top) and 3,3'-Dimethy1bipheny1 (bottom). Field Measured in Gauss ........... . ..... . ...... . ..... 57 Potential Energy Diagram for Biphenyl. (———) Biphenyl, (--°) Monosubstituted Biphenyls (---) Disubstituted Biphenyls........................ 69 VPC Trace for Photolyzed y-Azidobutyrophenone, COl-l and eel-4.000000.........OOOOOOOOOOOOOOOO 73 VPC Trace for Photolyzed G-Azidovalerophenone, Gel-1........OOOOOOOOOOOOOOOOO......IOOOCOOOOOO 74 Plot of Quantum Yield Versus % Conversion of y-Azidobutyrophenone at 313 nm (scale on left is for disappearance of ketone and 2-pheny1pyrrole and peak V; scale on right is for acetophenone and 2-pheny1-A1-pyrroline)..................... 79 Plot of Quantum Yield Versus % Conversion at 366 nm ( scale on left is for disappearance of ketone, 2-pheny1pyrrole and peak V, and 2—phenyl-A1- pyrroline; scale on right is for acetophenone). 80 Plot of Type II Quantum Yield Versus % Acetophenone Formation at 366 nm of G-Azido- valerophenone....................... ........... 84 Plot of Type II Quantum Yield Versus % Acetophenone Formation at 366 nm for y-Azido- butyrophenoneOOOOOOO0.0.0.0...00.000.000.000... 84 Plot of Type II Quantum Yield Versus [j-Azido- butyrophenon§]Irradiated at 366nm.............. 85 Stern-Volmer Quenching Plots of Butyrophenone by Butyl Azide and 2-(pffluorophenyl)-A1- pyrroline ..... . ................................ 85 xv LIST OF FIGURES (Continued) Figure XXVIII. XXIX. XXX. XXXI. XXXII. XXXIII. XXXIV. XXXV. XXXVI. XXXVII. XXXVIII. XXXIX. XL. XLI. XLII. XLIII. XLIV. Page Stern-Volmer Plots for the Azidoketones at 366 anOOOOOOOOOOOOOOOOOOOO00.............O. 86 Sensitization Plots of y-Azidobutyrophenone and G-Azidovalerophenone ...... . ..... . .......... 87 Hammett Plot of log of Relative Rate Versus GI. 98 Stern-Volmer Slopes for Type I Reaction of N-methyl- and N-benzyl-4-methyl-4-benzoyl- piperidineOOOO.....OOOOOOOOOOOO00.0.0.0... ..... 115 Stern-Volmer Slope for Type II Reaction from 1-methylcyclohexylphenyl Ketone by N-methyl- piperidine.........OOOOOOO......OOOOOOOOOOOO0.0 115 Stern-Volmer Plot for Benzaldehyde Formation of N-methyl—4-methyl-4-benzoy1piperidine....... 116 Stern-volmer Plot for Type II Formation of N-methyl-4-methyl-4-benzoylpiperidine........... 116 Sensitization Plot of N-methy1-4-methyl-4- benzoylpiperidine.............................. 118 Ground State Conformations of NMMBP.... ........ 122 IR Spectrum (top) and NMR Spectrum (bottom) of y-Azidobutyrophenone... ........ .............. 171 IR Spectrum (top) and NMR Spectrum (bottom) of 6-Azidova1erophenone........................ 172 Mass Spectrum from GC/Mass Spectral Data of y-Azidobutyrophenone (tOp) and G-Azido- valerOphenone (bottom)......................... 173 IR Spectrum (top) and NMR Spectrum (bottom) of e-Azidohexanophenone........................ 174 Mass Spectrum of e-AzidohexanOphenone.... ...... 175 IR Spectrum (top) and NMR Spectrum (bottom) of 6-Thiocyanonatova1erophenone................... 176 Mass Spectrum of 6-Thiocyanonatovalerophenone.. 177 IR Spectrum (top) and NMR Spectrum (bottom) of N-methyl-4-methyl-4-benzoylpiperidine.......... 178 xvi LIST OF FIGURES (Continued) Figure XLV O XLVI. XLVII. XLVIII. XLVIX. L. LI. LII. LIII. LIV. LV. LVI. LVII. Page Room Temperature Proton Decoupled 13C NMR Spectrum of N—methy1-4-methyl-4-benzo 1- piperidine with Freon 21 Serving as 1 F Lock... 179 Mass Spectrum of N-methy1-4-methy1-4-benzoyl- piperidine ..................................... 180 IR Spectrum of 2-methyl-5-methy1-6-phenyl-2- azabicyclo [3.1.1lhepta-6-ol: TOp (neat), bottom (nujol) ...................... .. ......... 181 NMR Spectrum of 2-methy1-5-methy1-6-phenyl-2- azabicyclo [3.1.3 hepta-6-ol.. ..... 182 Mass Spectrum of 2-methy1-5-methy1-6-pheny1-2- azabiCYClO [-3.101] hepta-G-Olo00.000.000.000... 183 IR Spectrum (top) and NMR Spectrum (bottom) of Phenyl-N-methyl-4-methylpiperidinemethanol..... 184 Mass Spectrum of Phenyl-N-methy1-4-methy1- piperidinemethan01.00............OOOOOOOOOOOOOO 185 IR Spectrum (top) and NMR Spectrum (bottom) of N-benzy1-4-methy1-4-benzoy1piperidine........... 186 Mass Spectrum of N-benzyl-4-methyl-4-benzoy1- piperidine...... ...... .......................... 187 VPC Trace for 1-methylcyclohexylphenyl Ketone (IV); Benzene (I), Octadecane (II), Type II product (III)ooooooooooo ...... coo.ooooooooooooooooooooo 188 A Typical VPC Trace for Analysis of Acetophenone (II) Versus Tetradecane (I).................... 189 A Typical VPC Trace for Analysis of Benzaldehyde (I) Versus Decyl alcohol (II).................. 189 'VPC Trace of N-methy1-4-methy1—4-benzoy1- piperidine(III); Naphthalene (I), Type II Product (II), Octadecane (IV)...... ............ 190 xvii INTRODUCTION Introductory Remarks: This thesis is composed of three overlapping but distinct problems. To avoid duplication of material, the Introduction is composed of one part, in which material relevant to each problem will be discussed as it applies under the specific heading. Thus each subject heading may deal with information relevant to one or more of the under- taken projects. The Experimental section is also composed of one part in which all the materials used in the various problems are presented. The Results section treats each project separately and the results of each project are followed immediately by the Discussion of those results. Objectives: The central objective of this thesis was to study sundry steric effects involved in energy and charge-transfer exchanges. Steric effects were involved in all three separate projects: (1) Determination of the size of grthgfsubstitu- ents necessary to force triplet biphenyl out of planarity and construction of a potential energy diagram for biphenyl. (2) The photochemistry of N-substituted—4-methy1-4-benzoyl piperidine. This kind of compound was interesting since the lone pair electrons located on nitrogen are held in a fairly rigid position relative to the carbonyl. Interaction of the lone pair electrons with the carbonyl moiety should be difficult in any conformation except the boat form. The rates for the various processes the ketone may undergo could be compared to those previously determined for the "model" compounds 1-methy1cyclohexyl phenyl ketone and y-dimethyl- aminobutyrophenone. (3) Determination of the rate of intra- molecular endothermic energy transfer from a triplet carbonyl group to an azido-group as a function of the number of methylenes separating them. This last problem included as minor objectives determination of the unmeasured OI value for the azido group, and of the amount of stabilization an azido group imparts to an adjacent radical center. In the course of this study all the major reactions of excited ketones were encountered. These include energy transfer, charge-transfer, hydrogen atom abstraction, and a-cleavage to radicals. Thus, the Introduction will continue with a brief survey of current knowledge about these reactions and will conclude with a brief description of each project. The presentation follows the following outline: (1) A Jablonski diagram showing the photophysical process under— gone be excited state molecules, particularly phenyl ketones; (2) Energy transfer mechanisms involving aspects of inter- molecular, intramolecular, and reversible exchanges; (3) Hydrogen abstraction processes relevant to the photoreduction of benzophenone and the Type II reactions; (4) Type I Photocleavage; (5) Inter-and intramolecular charge transfer mechanisms specifically related to amine quenching of carbonyls; (6) The triplet state of biphenyl; (7) Piperidyl phenyl ketones in relation to cyclohexyl phenyl ketones; (8) A discussion of the azide group during photoexcitation processes and a synopsis of triplet nitrene chemistry. Jablonski Diagram: The fate of electronic excitation in phenyl alkyl ketones is depicted in the modified Jablonskil diagram shown in Figure 1. The horizontal lines represent the lowest vibrational levels of different electronic states. The straight arrows represent radiative transitions and the wavy arrows non-radiative physical processes. The diagram depicts absorption of a photon to the excited singlet manifold with rapid internal conversion to the lowest vibration level of the first excited singlet. In benzophenone and most alkyl phenyl ketones the probability for isoenergetic intersystem crossing to the triplet manifold from the singlet manifold is unity2’3, thus radiationless decay from the singlet and fluorescence are negligible. Once the triplet state is formed the molecule rapidly relaxes to the lowest triplet vibrational level (necessarily lower than the singlet because of Hund's rule). Solvent and '8. Figure 1 Modified Jablonski Diagram substituents dictate the nature of the lowest triplet, since 3n,n* and 3 n,w* states have similar energies in alkyl phenyl ketones. Polar solvents and electron donating ring substitu— ents tend to lower the 3fi.fl* state relative to the 3n,n* state.4 Formally 3n,n* states arise via the promotion of a non-bonding electron on oxygen to an antibonding n* orbital, while 3n,fl* states involve the promotion of an electron from the u system to an anti-bonding 1F orbital. The nature of the lowest triplet naturally determines the rates of decay, phosphor- escence, and reaction. Phosphorescence of 3n,«* triplets characteristically has a much shorter lifetime than that of their 3n,1F counterparts4’5 and 3151? emission is much more 6'7 Wagner and Kemppainene, solvent and substituent dependent. by studying the rates of decay and Y-hydrogen abstraction of various alkyl phenyl ketones, have concluded that the two states are probably in thermal equilibrium and that the 3n,1F is responsible for all the reaction even when the 3n,1F is the lowest state. In the case of the biphenyls the intersystem crossing yield is not unity, so fluorescence, radiationless decay, and reaction from the singlet can compete with intersystem crossing to the triplet. The dotted line in Figure 1 indicates the strongly forbidden S+T* absorption process. When the ground and triplet states have the same geometry, S+T* absorption and T*+S phosphorescence spectra should be mirror images of each other and their 0-0 bands should overlap. Such is not the case either for phenyl ketones or for biphenyl,9 as discussed later. Energy Transfer: Probably the most general reaction excited states undergo is the process of energy transfer. This is the process whereby a donor molecule transfers its electronic excitation to a ground state acceptor(quencher). The acceptor ends up in an electronically excited state and the donor in its ground state. Energy transfer can occur both inter-and intramolecularly by three distinct mechanisms: (1) reabsorption by a ground state molecule of light emitted by a fluorescent donor; (2) dipolar or quadrupolar inter- actions between excited donor and ground state acceptor molecules, which accounts for singlet-singlet energy transfer over relatively long distances; and (3) exchange interactions which are responsible for triplet-triplet energy transfer.10 Several review chapters have been written on these processes. 11-13 The triplet-triplet energy transfer process is the most important with respect to phenyl ketones, since inter- system crossing yields are generally high. It involves a resonance exchange interaction which requires spatial overlap of the orbitals of donor and acceptor.15"20 Uncertainty in just how close donor and acceptor must come to promote the exchange interaction required for the transfer has elicited a search for steric effects in triplet-triplet energy transfer processeszo-zz. Wagner and McGrath23 have shown that donor and acceptor do not have to approach within bonding distance to achieve actual transfer. Dexter16 presented equation (1) to describe the depen- dence of rates of exchange-induced energy transfer on the distance R between donor and acceptor, where L is a fixed ket=Y exp (-2R/L) (1) distance related to the "average effective Bohr radius" (which has never been specified) and Y includes several parameters related to spin statistics and orbital overlap. Under conditions when exothermic energy transfer between triplet ketone and diene molecules in a solvent cage occurs, R is close to the sum of the van der Walls radii, 3.5-4AH The rate constant, k for this process in benzene has been et' measured at 5 x 109 M"1 sec—1.15'18'24”26 Cowan and Baum27 have measured ket values from 1 x 1011 to 3 x 109 M.1 sec-1 for intramolecular energy transfer in styryl ketones where the separation between donor and acceptor varies from 2 to 4 methylene groups. In the ketones studied, the number of conformations in which the two ends of the molecule are in contact decreases rapidly with an increasing number of methylene groups. It has been estimated that every 1.2 A increase in R results in an order of magnitude decrease in 23,28 ket. measured by Cowan contain some measure of the rates of It is quite possible that the observed rates rotation of the olefin about the methylene chain or some measure of the ring strain formed in the energy transfer process. The rate of exothermic triplet energy transfer in solution is influenced by the viscosity of the solventll'ls’ 17'29'30. In moderately viscous alcohols, glycolS: or parafin oil-hexane mixtures, the quenching rate constant k is inversely proportional to viscosity, n, according et . . . 15,31 to the modified Debye equation (2) . k k “8RT/2000n (2) et= diff— In less viscous solvents, the quenching rate constant still increases as the viscosity decreases but becomes lower than the calculated diffusion-controlled rate, indicating that there is inefficiency in the energy transfer process and that diffusion apart of the donor and acceptor can compete with energy transfer during the lifetime of a solution 15 encounter. The theoretical implication of ke being less t than kdiff for exothermic triplet energy transfer in solvents of low viscosity may be that there is a preferred relative configuration of the donor and acceptor molecules, or simply that R does not get small enough.23 When the donor and acceptor have similar enough triplet energies such that energy transfer is reversible, the actually observed rate constant is given by equation (3) and depends on the donor concentration.19 k et REES: _ _ (3) 1+k-eti D_/ In benzene at room temperature, the rate constant for 9 M"1 sec.1 when triplet energy transfer 15,18,24,26 quenching is 5 x 10 is exothermic and irreversible (AE23—4 kcal/mole). 17,19 When reverse energy transfer from the excited acceptor back to the original donor is possible, it appears that the 9 M”1 sec-1, even where rate of quenching is still 5 x 10 the energy transfer process is only 1 kcal/mole exothermic. The notion that vertical triplet energy transfer in solution proceeds at the same maximum rate as long as it is exothermic was originally proposed by Sandroslg, who first presented the kinetic treatment for reversible energy transfer. This treatment is similar to the ones used for the quenching of the photoreduction of benzophenone, where the triplet energies of the donor and acceptor are nearly identical.9 Knowledge of energy transfer rates is not only interesting in itself, but such concepts can be used for measuring excited state lifetimes. The most common technique for doing so involves Stern-VOlmer quenching studies. This process is exemplified by the photoreduction of benzophenone presented in Scheme 1 where HD is a hydrogen donor and Q is a quencher molecule. ”'3 <<:>>E @EW .3“. (Ox- 2 .0g 10 3 e O c- O (4) a OH k f? * kd. (9) (10) 7 \ Scheme I Mechanism for the Photoreduction of Benzophenone Straightforward Stern-Volmer analysis (ignoring the reversible energy transfer equations 8 and 9) yields equation (11): 11 45 k /-Q 7 o __ __ _ __ et_ _ (11) T _ 1 + ketT-/- Q_/ — 1 +Td + khlfSP—7 Equation (12) (which includes steps 8 and 9) substitutes equation (3) for ke : t k 1170‘7 ¢o = l + et k (12) 9 /—K 7 1 + -et— _ kd' Equation (12) also describes the inverse relationship between the slopes of the Stern-Volmer plots and ketone concentration. Letting S equal the slope of a given Stern-Volmer, equation (13) results: (13) The intercept of a plot of 1/8 versus 1—K47 gives the true ketT value for the quencher in question and the slope divided by the intercept equals k-et/kd' 12 Hydrogen-Atom Abstraction It has thus far been assumed that the species responsible for reactions involving carbonyl compounds is largely the triplet. Evidence for the triplet multipli- city of the excited state responsible for photoreduction and the Type II reaction comes from both chemical and spectro- scopic evidence. Hammond measured the excited state life- times of benzophenone in several solvent systems,32'33 finding them much too long to be singlets. Backstrom and Sandros34 sensitized the phosphorescence emission of biacetyl with benzophenone, and Terenin and Ermolaevl4 observed that in EPA glass at 770 K benzophenone sensitizes the phosphores- cence of naphthalene while simultaneously quenching its own phosphorescence. Both of these triplet quenchers (naphthalene 8 biacetyl) also quench ketone photoreduction. Walling and 36 have found that the behavior of the Gibian35 and Padwa carbonyl triplet parallels very closely that of Egrtfbutoxy radicals in hydrogen abstraction reactions. (a) Photoreduction of Benzophenone: Although photoreduction has always played an essential role in nature in the utilization of CO by plants, products 2 from even "simple" laboratory systems were not characterized until 1900, when Ciamician and Silber37 first identified beaninacol and acetone as the photOproducts from the action of sunlight on an iSOpropanol solution of benzophenone. Many other substrates have also been used as the hydrogen 13 source, including alkanes,36 amines,38 alkyl benzenes32 and tributylstannane.39 Since 1900 the photoreduction of benzophenone has been the subject of a plethora of studies, so that at the present time its mechanism is pretty well determined. In fact the photoreduction of benZOphenone by benzhydrol has been used . 40 as an actinometer. A recent review article concerning the mechanism of the photoreduction and rates of hydrogen abstraction from various substrates by a variety of carbonyl compounds has been published.82 The mechanism for the photo- reduction of benZOphenone is shown in Scheme 1. Thus this system should serve as a good monitor for measuring rates of energy transfer to, and thus the triplet energies of, various substituted biphenyls. Although the photoreduction of benzophenone has been the subject of many studies, some minor points of its mechanism are still subject to controversy. The major controversy centers around the explanation of the yellow 41-43 The color which develops during the photoreduction. origin of this color has been found to be a long-lived intermediate whose nature has remained in doubt for nearly fifteen years. Recently, the enol coupling product (analogous to 1-diphenylmethylene-4-trityl-2,5—cyclohexa- diene formed in the case of hexaphenylethane44) was prOposed for this intermediate by several independent workers.45-47 14 OH CH .£ ©ng “ {- CH3 Wagner48 has estimated that for the photoreduction of benZOphenone by benzhydrol, no more than 10% of the radicals produced form the coupled intermediates. Weiner49 has questioned the intermediacy of such structures in the photo- reduction. However, more recently, Lamb50 presented product analysis studies on sterically hindered benzophenones which clearly indicate such coupled products are indeed formed. (b) Type II Photoreaction: Coincident with the developments in the photoreduction processes investigators were studying the Type II photo- elimination process originally discovered by Norrish51. Noyes52 first suggested that the Type II reaction proceeds by the intramolecular transfer of a y-hydrogen yielding an olefin and an enol; the enol then rearranges to the carbonyl compound. The abstraction of the y-hydrogen has been firmly established53'S4 61 and Yang first observed that cyclobutanols are generally formed in conjunction with the elimination. The most compelling evidence for the presence of a 1,4- biradical gig the 1,5-hydrogen shift has been presented by Wagner and Kelso. The photolysis of B,y-diphenylbutyrophenone produced no triplet stilbene from triplet ketone even though energy and Spin considerations showed that such a process could have proceeded concertedly. The combined quantum yield 15 for a,B-c1eavage, cyclization, and racemization of (4S)-(+)- methyl-1-pheny1-1-hexanone (MPH) was very near unity. Alcohol solvent caused the product quantum yield to be essentially unity while eliminating racemization of starting material. Thus, racemization and products arose from the same biradical intermediate. Furthermore, the biradical of valerophenone was actually trapped using alkyl thiols as trapping agents.183 The mechanism for the Type II reaction can then be represented as in Scheme II: ~3.8% H "CHCH3 CHCH; / f.) ' CH OH .3" C 3 //i\~//FCH3 Ph/’ Ph ' OH M K m95% Ph OH Ph HO + ,_J WV OH OH 2R 0 OH _ m25% ' __’ph/l\ + Wl/\+Ph —\ Ph W70% (I) O p.) (_+_) Scheme II Mechanism for Type II Reaction 16 The effect of substituents on the triplet state reactivity of phenyl alkyl ketones is continuing to be investigated. Electron withdrawing groups on the aromatic ring decrease the probability for product formation from the biradical by enhancing disproportionation to Type II products; electron donating groups have the Opposite effect. 56'57 Strong electron withdrawing ring substituents double the triplet state reactivity, apparently by a simple inductive effect on the electrophilic 3n,n* carbonyl moiety.56 Phenyl ketones having 7- and 6-substituents show relative triplet state reactivities corresponding to the known reactivities of the various kinds of C-H bonds in the y—position.4’58 Ketones with y- and 6-electron with- drawing groups have enhanced quantum yields in spite of their diminished rates of hydrogen abstraction. Apparently the reduced disproportionation of the biradical reflects the reduced nucleophilicity of the y-radical site of the biradical. Quantum yields decrease with electron donating y- and 6-substituents indicating enhanced disproportionation of the 1,4-biradical. Wagner and Kemppainen59 first indicated that Type II quantum yields do not directly relate to triplet state reactivity. Conversely they60 have reported that rates of y-hydrogen abstraction for various 6- and e-substituted ketones do correlate with the a values of the various I substituents. By estimating the p value of the y-substituted 17 60 ketones as -4.3 , the inductive and radical stabilizing effects of the y-substituents can quantitatively be separated. Thus the ability of various substituents to stabilize a radical were calculated. 62-66 Lewis has recently reported on the photochemistry of several conformationally interesting phenyl ketones, where the rates of y-hydrogen abstraction are drastically affected by the geometry of the molecule. He62 first noted that a-substitution increases the ratio of cyclobutanol formation to photoelimination products. Such substitution of a-methyl groups in alkyl phenyl ketones also leads to some competing a-cleavage. Type I Photocleavage: The Type I processes of ketones invohnaa-scission to give acyl and alkyl free radicals67 which go on to form various stable products. In the case of ketones with differ- ing degrees of alkyl substitution, Type I cleavage generally results in the formation of the more stable alkyl radical and the corresponding acyl radical.68 In alkyl phenyl ketones containing a—substituents, the rate of the Type I process is fast enough to compete with the Type II process. 69 Wagner and McGrath have indicated that the rate of a- cleavage for a,a-dimethylvalerophenone is 1.4 x 107 sec-l. This value is similar to the rates of a-cleavage obtained 7 for exo-Z—benzoyl-2~methy1norbornane (1.2 x 10 sec-1) and 7 l-methylcyclopentyl phenyl ketone (1.3 x 10 sec-1) reported 18 . 64 . 66 by Lers. Johnson and Lewis measured the rate of a— cleavage for l-methylcyclohexylphenyl ketone as 2.5 x 107 sec' . However, this value is probably slightly high for reasons to be discussed below. Triplet phenyl t—butyl ketone cleaves with a rate of 2.3 x 107.70 Triplet aliphatic E-butylketones whether they contain either a-substituents or y-hydrogens a-cleave about 4000 times faster than phenyl alkyl ketones containing a-substitu- ents. The exact reason for this difference in rates between aliphatic ketones and phenyl alkyl ketones is not known, although it is probably due primarily to energetic differences or differences in geometry. It may be noted, however, that triplet phenyl ketones resemble triplet aliphatic ketones in rates of hydrogen abstraction4 and singlet aliphatic ketones in rates of a-cleavage.7l'72 Charge-Transfer: A charge-transfer complex is defined as a combination of a donor and acceptor which exhibits a special light absorption called a charge-transfer transition. In its broadest terms it includes the newer concepts of excimers and exciplexes. The concept of charge-transfer was first formulated by Mulliken73 to explain the fact that iodine dissolved in carbon tetrachloride is violet while in benzene solution it is brown. Charge transfer interactions are small in the ground state and often difficult to distinguish from other types of electrical interactions such as mutual 19 74 75 polarization. Interestingly, Leonhardt and Weller demonstrated by flash-spectrosc0pic investigations of perylene solutions containing amine that electron transfer, not possible between the ground state donor and acceptor, could occur when the molecule was electronically excited. Mataga and Ezumi76 observed long-wavelength fluorescence from some aromatic hydrocarbons in N,N-dimethyl aromatic amine solvents. This in conjunction with the electron affinities of the excited aromatic hydrocarbons and the ionization potentials of the amines led Mataga and EZumi to conclude that the interaction between excited hydrocarbon and amine involved charge transfer from the amine to the excited hydrocarbon. The ionization potentials of amines have been correlated with the rate of interaction between amine and electronically excited ketone. Davis77 found that the efficiency of quenching of fluorenone fluorescence by various amines varied inversely with the ionization potential of the amine. Cohen and Stein78 showed that amines with lower ionization potentials were more reactive in the photoreduction of 4-benzoy1benzoate anion than those amines with higher ioni- zation potentials. (A) Intermolecular: Aromatic ketones can be photoreduced efficiently in the presence of molecules bearing the -CHN-group79. For example, triethyl amine81 reduces triplet 2-acetonaphthone about one thousand times faster than does ethanol. Triplet 20 fluorenone abstracts hydrogens from tributylstannane about one tenth as fast as it interacts with triethylamine83. Moreover, by quenching the photoreduction of benzophenone by 2-buty1amine with naphthalene, the rate of reaction was determined to be about 5 x 107 M—1 sec"l 84, which is more than an order of magnitude greater than that found when benzhydrol or 2-pr0panol are the hydrogen sources. Yet benZOphenone interacts with triethylamine three orders of 80 magnitude faster than with iSOprOpyl alcohol. Since the rate of quenching by amines of ketone phosphorescence and fluorescence is faster than the observed rate of photo- reduction83, the rate of interaction of the donor and acceptor is faster than the rate of hydrogen transfer. Thus the following mechanism has been proposed.85 > R2COH+RCHNR2 *3 u R C=O +RCH NR _ o — 0+ .— 2 2 2 >1 2C-O R NCHZR/ 2 The intermediate can either form products or revert back to the ground state amine and ketone. Davidson85 by the use of flash techniques has observed a transient with an absorption maxima at 670 nm which he attributes to the amine cation. Further support for the above charge-transfer interaction between ketone triplet and the non-bonding electrons of nitrogen, followed by reverse-charge-transfer or proton transfer is given by: (l) the efficiency with which tri- 86 ethylenediamine photoreduces benzophenone ; (2) the inverse isotope effect observed for 2-buty1amine-N,N-d2 and 21 cyclohexylamine-N,N-d286; (3) the fact that Optically active 2-butylamine is not racemized during the reactionax and (4) the lower quantum yields of benzophenone disappearance observed with amines as the hydrogen source relative to alcohols as the hydrogen source.84 Guttenplan and Cohen83 have shown by plotting the rate constants for interaction of benzophenone triplets with a variety of donors versus the electron affinity of the donors that complete electron transfer does not take place. Further evidence that complete electron transfer does not take place in the charge-transfer interactions of ketones and amines 83 is that only small solvent effects are observed for the ketone systems relative to those systems where full electron transfer does occur.75 Wagner and Kemppainen observed no increase in the quenching rate with which triethylamine and t-butylamine quench valerOphenone in acetonitrile relative to that in benzene and the quenching rate decreased in methanol. (B) Intramolecular: The intramolecular Type II reaction shows close parallels with intermolecular photoreduction when amines are involved. 87-89 Wagner and Jellinek,89 while studying alkylamino phenyl ketones of varying methylene chain length, observed that the intersystem crossing yield decreases and the rate of quenching by the amino group increases as the amino group moves closer to the carbonyl moiety. These results indicate that intramolecular charge-transfer quenching 22 competes with intersystem crossing and the Type II reaction. Wagner and Kemppainen88 also concluded that the geometry of the charge transfer state must be such that the y-hydrogens are held away from the carbonyl oxygen, yet the nitrogen must be close enough to the oxygen to hold the complex in a cyclic configuration. The behavior of y-dimethylamino- butyrophenone in benzene is reproduced in Scheme III. n:g* 58% n,n 3 42% O-//:%V //©/ / G (W 0 Type II .3, 13’ products ‘\\¢/A\\// \R Scheme III Behavior of Y-DimethylaminobutyroPhenomain Benzene Biphenyl: For the past couple of decades photochemists have been intrigued by the triplet state geometries of excited states. That biphenyl should not escape this scrutiny is not surprising. Gardner90 predicted the excited state geometry 23 of biphenyl. Application of a semi-empirical exciton theory coupled with ESR data predicted a value of 260 between the two phenyl rings. A month earlier, however, Wagner9 concluded that the triplet state of biphenyl prefers to be planar. This conclusion was based on two distinct pieces of evidence: First, the eXlstence of a 10 kcal difference between the 0,0 band for phosphorescence and S+T absorption: Second, the fact that naphthalene and conjugated dienes are 2.5 times more effective than biphenyl at quenching triplet butyrophenone and at least 20 times more effective than biphenyl at quenching triplet benzophenone. It was also noted that the actual efficiency with which biphenyl quenches the photoreduction of benzophenone decreases with increasing benzophenone concentration because of reversible energy transfer. A brief study of grthgfsubstituted biphenyls showed them to be less efficient quenchers of the benzo- pheone photoreduction than biphenyl itself. About the same time that Wagner reported his results, Brinen and Orloff91 reported the D value of biphenyl. They first calculated the expected D value (0.116), then measured it (0.110). Good agreement between calculations and experimental results were not obtained until the calculations assumed considerable double bond character inherent in the 1—1' bond. The conclusion that triplet biphenyl is planar has since 92-94 been reinforced by several spectroscopic and theoretical95 24 investigations. Moreover, Mispelter94, while studying 3,3'-difluorobiphenyl, hinted that there are two triplets observable in the ESR and that there is little or no spin localized at the three position. The spectrum was complicated by fluorine hyperfine splittings, but computer (CAT) analysis indicated two triplet species with different E values but identical D values. The determination of the triplet state geometry of biphenyl and its analogues and the size of orthgfsubstituents necessary to force triplet biphenyl out Of planarity has a practical significance. Certain commercially available pesticides (Arochlors) contain polychlorobiphenyls whose decomposition upon exposure to sunlight in the environment is of importance. At least one study has been undertaken on these polychlorobiphenylng. The triplet state geometry is also important in studies of the photoracemization Of Optically active biphenyls.97 NfSubstituted-4-Methy1-4-Benzoylpiperidine: The study Of N-methyl-4-methyl-4-benzoylpiperidine (NMMBP) is interesting on two accounts. First, very few photochemical studies on pharmacologically active substances have been performed.98 This type of study would appear to be useful for determining shelf-life and/or the synthesis of novel compounds. NMMBP is potentially active as an 99 analgesic, sedative (Demerol-Type). Its Type II cyclization photoproduct is a potential stimulant (Amphetamine-Type). 25 Secondly, photochemically the compound is interesting because when the nitrogen containing the lone pair electrons is located in a ring, charge-transfer interactions between the carbonyl and nitrogen lone pair electrons should be less efficient than in a freely rotating compound. Stabilization by the lone pair electrons of the incipient radical in the Type II reaction should afford an extremely short-lived triplet. The photochemical behavior of these compounds should be comparable to the two compounds representing the extremes of behavior: l-methylcyclohexyl phenyl ketone (MCPK) and y-dimethylaminobutyrophenone. Substitution of different groups on the nitrogen atom of NMMBP might give some insight into the effects caused by such substitu- tion on ground state conformations involving the lone pair electrons. Lewis66 reported that quenching of the competing Type I and Type II reactions of MCPK produced different qu values while 1-methy1cyclopentyl phenyl ketone gives the same qu value for both Type I and Type II processes. These results indicate that MCPK undergoes the different reactions from two conformationally distinct triplets (Figure II). 26 0* Type I u C-Ph E ...—9 Type II 9—— ‘5‘” 1K (\ I?11 hv hv O H C-Ph ~ '—" 6—... Ph Figure II Photochemical Scheme for l—Methylcyclohexylphenyl Ketone This conclusion demands that the energy barrier for excited state conformational isomerization is higher than the acti- vation energy for formation of Type I or Type II products. It should be noted that in Lewis' original report the possibility that one isomer might sensitize the other was neglected. In any event the photochemistry of the amino- ketone NMMBP should provide behavior quite similar to that observed for MCPK. The quantum yield and quenching slope for the Type I reaction of NMMBP should be almost identical to that observed for MCPK. since the lone pair electrons on nitrogen should not be able to interact with the benzoyl group when it is in 27 the equatorial position. The Type II reaction of NMMBP should be much faster than that observed for MCPK, because the lone pair electrons are in an orbital which is parallel to the incipient radical orbital. Thus the lifetime of the triplet formed from the Type II conformer of NMMBP should be shorter than that observed for MCPK. Since the boat conformation of NMMBP seems to be an unlikely species, charge-transfer quenching of the carbonyl by the amino group should be negligible. Azidoalkyl Phenyl Ketones: Since these compounds consist of two groups which can independently absorb incident light which impinges on the molecule, they can be called "bichromOphoric". Relatively little is known about the excited state interactions of molecules containing two chromophores which do not interact in the ground state, although a few recent reports concerning such molecules are quite intriguing. Cowan and Baum27 have measured the rate of energy transfer from a carbonyl to a styryl moiety separated by a varying number of methylene groups. Wagner and Nakahira100 have irradiated several dibenzoyl ketones whose individual benzoyl groups were separated by a varying number of methylene groups. Hammond101 has studied the rates of energy transfer between a benzo- phenone and the naphthalene moiety separated by a varying 102-104 number of methylene groups. Several other studies have been undertaken. 28 The study of the bichromOphoric azidoketones has the added attraction that the rate of the Type II reaction should be competitive with the rate of energy transfer from the carbonyl to the azide group. As pointed out in the Type II section, from the rates of the Type II reaction it is possible to determine the previously unmeasured OI value of the azido group and the ability of the azido group to stabilize a radical. Also, since the azido group can undergo many interesting reactions, the confinement Of the azido group to the same molecule with a carbonyl group might lead to new compounds or novel mechanisms. The Azido Group: The azide group is one of the most useful and versatile groups available to the Organic Chemist, yet its modes Of photochemical reactions remain somewhat of a mystery. Its properties are classed with the group of inorganic radicals called the pseudohalides, and it possesses both a -I and a +R effect. In aromatic substitution reactions the group is pan-activating.105 It can be used to synthesize a number of heterocyclic ring systems (tetrazoles,triazoles, oxazoles, carbozoles, etc.)106. It can be used to form imines, amines, amides (Schmidt reaction), azo compounds, and penicillins.107. Its inorganic salts can be explosive (copper azide). The group is both thermally and photochemically active. In fact, the photosensitized decomposition of the azide group has 108 I potential importance in photographic applications and 29 the groups pharmacological properties are just beginning to 109 Since no quantitative photochemical be investigated. studies have been performed on compounds containing the azido moiety, it seemed worthwhile to measure its a value, I its ability to stabilize a radical, and the rates of energy transfer to it from a nearby carbonyl group. (a) The Azide Excited State: Effortsllo-114 to relate the observed UV bands of alkyl azides (215 and 285 nm) with known types of spectrOSCOpic transitions have been attempted. 'However, the exact nature of the transitions observed in the UV spectra of covalent alkyl azides is not known with any certainty. In fact it is not even certain whether these bands are due to 191! transi- 110 tions or n,1# transitions. It has been reported that the 285 nm transition involves the Py and Px (presumed 1§+W; transition) electrons. This transition is shown in Figure III. 2 P Y pr .W. x-.“_ (11462 i 1% )IPx_ O "A"- by + ..-... / a N NC 1' N5'_Nb_Nc 5 /Na-Nb-NC / R R ............ Figure III fly+1k Transition in Alkyl Azides As seen in Figure III, the ny+n§ transition leaves the P 114 Y orbital on the Na atom somewhat electron deficient. 30 115 have attempted to measure the Lewis and Saunders triplet energy of the azido group. Sensitized decomposition of the azides allowed calculation of rates of energy transfer. Even with the sensitizer of highest triplet energy (cyclo- propyl phenyl ketone) an energy transfer rate equal to that of the rate of diffusion was not obtained. This result suggested an energy of 75-80 kcal/mole for the triplet. In this same study a Hfickel calculation indicated that the first excited state of methyl azide is bent and shows two minima at about 1400 and 220°. The transoid configuration was shown to be slightly more stable than the configuration with the methyl group out of the plane in which the three nitrogen atoms reside. Roberts116 has shown that only 0.6 ev (less than 20 kcal) is required to bend a ground state azide from a linear arrangement to an angle of 120°. The ability of the azide group to bend from a linear arrangement is dramatized in the synthesis of triazoles and tetrazoles. (b) Decomposition to Nitrenes: Physical proof for the existence of organic nitrenes appeared only recently in the literature. Yager117 reported the ESR signals of stable aromatic nitrenes at 770 K which are characteristic of two strongly interacting unpaired electrons on a single atom. Similar spectra were Observed 118 119 upon photolysis of alkyl azides at 4° K. Reiser has Observed the nitrene from 1-azidoanthracene in flash photolysis 120 experiments, and recently Lehman and Berry have observed 2-nitrenobiphenyl under similar conditions. A large body 31 Of chemical evidence for the existence of discrete nitrenes exists in the 1iterature.l19'122_125 However, Abramovitch126 has recently reported that in certain alkyl migrations to the electron deficient Na atom, a concerted mechanism is probably involved. In the direct photolysis of azides four theoretically distinct species can form: singlet azide, triplet azide, singlet nitrene, and triplet nitrene (in triplet sensitized studies only triplet azide and triplet nitrene should form). The problem of determining which of the four species are formed and which give rise to specific products is not easy to discern. This problem is superbly illustrated by the photolysis of 2-azidobiphenyl. Q @C. Swenton127 photolyzed 2-azidobiphenyl and found a 71% chemical yield of carbazole and 8% azocompound upon direct irradiation. In the presence of acetophenone (triplet sensitizer), a 43% chemical yield of the azo compound plus an 8% yield of the carbazol was found. Direct irradiation in the presence of piperylene (triplet quencher) produced a yield Of 89% carbazole and 4% azo compound. Lehman and 120 Berry have recently measured the rate constant for the carbazole closure reaction at 103 sec_1 and in the process followed the reaction by flash studies. The results of Lehman and Berry indicate that the singlet azide decomposes 32 tO the singlet nitrene which either closes to the carbazole or undergoes fast intersystem crossing to the triplet nitrene to form the carbazole. Both the results of Swenton and of Lehman and Berry are consistent with the fact that singlet nitrene closure is competitive with nitrene inter- system crossing. The azo compound presumably comes from the triplet state of the azide rather than from the triplet nitrene. However, this mechanism is not proven unequivocally. Since this thesis is concerned primarily with the triplet excited state, the following reactions of triplet nitrenes or of triplet azides are listed with brief comments: 1) Rearrangement: This reaction is probably the most general reaction of alkyl nitrenes. The imine is the favored product. 128 RZCH—N° —> R2-C=NH (14) 129 2) Hydrogen Abstraction: Aromatic nitrenes abstract hydrogens from ethanol with a rate constant about 2.4 x 102 1 mole-1 sec-1. In the reaction some amine is formed and a certain probability of radical recombination exists. Barton130 originally reported that the photolysis of n-butylazide produced pyrrolidine by a 1,5 hydrogen shift and closure Of the resulting diradical. The formation of pyrrolidine has 131 132 since been shown by Barton and others not to occur. 3) Addition to Double Bonds: Triplet nitrenes add to double bonds in a two step non—stereospecific fashion to form aziridine5133'134. The mechanism is probably similar to 33 that for the addition of nitrene to aromatic systems to produce azepines.135:l36 4) Coupling to Form Azo Compounds: 2RN+RN=NR (15) 129 Reiser has shown that this process is diffusion controlled for aromatic nitrenes. 5) Reaction of the Nitrene with the Azide Group: This process accounts for a large prOportion Of decomposition of the azide and accounts for the high quantum yield of nitrogen evolution in the photolysis of azides in the gas phase. R—N- + RN +R-N=NR + N (16) 3 2 129 has shown that this process is also diffusion Reiser controlled for aromatic nitrenes. Nitrenes also react with other atoms which possess electron pairs: such as amines,134 the nitro group,137 138 139 the carbonyl group, and dimethyl sulfoxide. (c) Products from the BichromOphoric Azido Alkyl Phenyl Ketones: Incorporation of the azido and carbonyl groups in the same molecule should, upon excitation, give energy transfer from one group to the other. If excitation is initially located in the carbonyl group, the reactions shown in Scheme IV can be envisioned. The references for these "a priori" reactions can be found in the former sections. 34 O I) C / W 3 O ’x io n " /—NH o 2 \h" \ O “ 0* n r—-N3 ket ? /—N§ Q/jVCHZ)n ——————_)<©/C\_—(CH2)n k/ H —-NH 2.) my“ 0%“ ”“2“ 3 O J, 0 sz ©/\3- ©C \(CI‘N)= nN_\(c1-§)Cn\. + 2\ng/ (CH2)n_3-N3 ”FICH2)n_3-N3 { HO < 1 Scheme IV Possible Products From Photolysis Of Azido Ketones PART I TRIPLET BIPHENYL RESULTS Quenching of triplet benzophenone by Biphenyls: The efficiencies with which naphthalene, biphenyl, 2-, 3-, and 4-chlorobiphenyl, and 2-, and 4-methy1biphenyl quench the triplet state of benzophenone in benzene were determined by either one or both of two methods. In method I degassed benzene solutions containing fixed concentrations of benzophenone, 0.5 M isopropropyl alcohol, and varying concentrations of the quenchers listed above were irradiated in parallel at 250 C with the 365 nm region of a mercury arc. Disappearance of ketone was monitored by UV analysis. After irradiation each tube was opened and the contents poured into a vial which was kept in the dark for 15-24 hours. This pre-analysis procedure was employed since the UV absorbance of samples immediately after irradia- tion was high and decreased slowly to steady values. This phenomenon is probably related to the formation of thermally unstable radical-coupling products.4l.43 In method II the phosphorescence of benzOphenone in degassed benzene solutions was quenched. The phosphores- cence was measured, Oxygen was bubbled into the tube and the phosphorescence intensity remeasured. This background reading was subtracted from the initial sample reading. Stern-Volmer 35 36 plots of 40/4 versus quencher concentrations were linear fortjua two methods employed and yielded the slopes (ktT) listed in Table I. Quenching rate constants increase with decreasing ketone concentration for biphenyl, 3- and 4-chlorobiphenyl, and 4-methy1biphenyl, but apparently not for 2-chloro- and Z-methylbiphenyl. Such dependence of ktT on ketone concen- tration indicates reversible energy transfer.9 Figures IV- XII display the dependence of kt't for these quenchers on ketone concentration. Table II lists actual ktT values (l/intercept) Obtained from equation (13) (Introduction) and Figures XI and XII. With k assumed equal to 5 x 109 t Mnlsec-1 for naphthalene26 the ‘I value for triplet benzo- phenone in benzene and 0.5 M isopropanol can be calculated (Table II). With the aid of the known ‘f values, the kt values for the biphenyls can be calculated (equation 13, Table II). The slopes divided by the intercepts of the plots in Figures XI and XII give the k-t/kd' values listed in Table II. Assuming the estimated kd' value of 3 x 105 48 can be applied to the present system, k_t can be calculated for the biphenyls in isopropanol-benzene solvent. Since k d' can be expected to change in going from isopropanol-benzene solvent to pure benzene, the k_t value Obtained in the isopropanol-benzene for biphenyl was used to calculate a kd. value in benzene. That these estimated kd, values are in the correct ballpark is evidenced by the work of Ruzo and Zabik55 who report that unhindered polychlorinated biphenyls 37 have kd, values approximately 4 x 107 sec-1. The change in solvent from benzene to iSOprOpanOl-benzene should have little effect on k moreover any effect the change in solvent t! does have on kt would effect k_ to the same degree. t Absorption Spectra of Biphenyls: Absorption spectra of the biphenyls in heptane or ethanol solutions are quite similar. All the biphenyls, like biphenyl itself, display an intense, structureless band with Amax near 250 nm corresponding to the lA-tlL transition of benzene. Table III lists the Amax values and molar extinction coefficients for the chloro- and methyl- biphenyls. Meta-substitution whether chlorine or methyl produces only a slight change compared to biphenyl. A para- chlorine produces a red shift (740 cm-1, 2.1 kcal/mole) and intensity enhancement as does para-methyl (845 cm-1, 2.4 kcal/mole) and di-para-methyl (1,248 cm‘l, 3.7 kcal/ mole) substitution; an ortho-chlorine cuts the intensity in half and produces a more sizable blue shift (1100 cm_l, 3.1 kcal/mole) similar to the ortho-methyl (2,182 om'l, 6.2 kcal/mole) and di-ortho-methyl (3,681 cm-l, 10.5 kcal/ Inole) substitution. These effects are well documented.140 JPhOsphorescence Spectra of Biphenyls Phosphorescence spectra were recorded at 770 K in methyl- cY’Cfllohexane and cyclohexane for all the biphenyls. The spe<=tra of the chlorobiphenyls were also obtained in heptane. All the biphenyls phosphoresce strongly with the 38 Table I Quenching Data of Triplet Benzophenone by Biphenyls in Benzene Quencher Ketone Conc.(M) Sa,M-1 Sb, M-1 Naphthalene 0.054 4335:1025C 40,000 biphenyl 0.054 26.3:0.1: 24d 103 0.035 ------ 152:15 0.02 4911.0 250 0.0075 68 1286 4-chlorobiphenyl 0.054 164:3 -—-- 0.035 217:3 ---- 0.02 346 ---- 0.0075 500 ---- 3-Chlorobipheny1 0.054 89 ---— 0.025 144 ---- 0.0083 219 ---- 2-Chlorobiphenyl 0.054 1.13 11.8 0.035 ---- l3.9:0.2 0.02 ---- 11.2 0.0075 ---- 11.7 2-methy1biphenyle 0.052 ---- 96 0.0131 ---- 95 4-methylbipheny1 0.035 ---- 520 0.025 ---- 716 0.017 ---- 833 0.0088 ---- 2425:425 aQuenching of photoreduction in 0.5 M iSOprOpanol (method 1); S with slope obtained from the Stern-Volmer plots of Figures IV, V, VIII and X. bQuenching of phosphorescence in benzene (method 2); S.is the slope obtained from the Stern-Volmer plots of Figures VI, VII, and Ix. cThe error cited here is the actual range of values obtained If no error is indicated the standard deviation of the run can be found in the experimental. for two or more runs. dQuenching of phosphorescence in 0.5 M isopropanol. eTwo points only for both determinations. 39 .mm mocmuwmmm p .qoa x v on Hmsqm .px Eoum pmumHOOHMOO .hoa x mn.a 0» assoc unx mean: .Ox\uux Eoum Omumasoamun o u: .HHx was Hx mmusmwm Boom admoumuca on» an pmpfl>flp mmmon on» was mmsHm> . x\ x was mummoumucw pmusmmmfi may one m.eux «Amav :Owumsvm How cowuosponucH cw Umswmmp mmonu mum mmHQMHHM>m --- --- ooh ooh --- --- ooo.oe mmme osoamsusoms --- ooms.o o.m --- ems --- oooe --- assossasasssoz-e --- o maa.o --- o --- m.mm --- assosoasassuozum --- mm.a --- ee.m --- mo --- mos assosoasosoarous --- om.a --- mm.m nu. ma 4-- omm assosoasosoasoum --- o mao.o mao.o o o H.NH ma.a assosoaoosoasoum o.s ms.a ~H.m H~.H mme mm oomm mos assosoam moan mm“ moan mmw moan mmw eons.os moaxsns soaxsx mosses .oxxuux .ox\uux has ..us sosososo mmcocmnmoNcmm umamwua mo OGMSOGOSO Haswnmflm MOM mnmumemumm owumcflm HH OHQMB 4 3 O _O 0 2 1 Figure IV: 5 4 3 q, 2 _0 Figure V: 40 0.054 M benzophenone 9 0.02 M benzophenone 0 0.0075 M benzophenone I l J L 1 2 3 4 x 10‘ ZfBipheny147 Stern-Volmer Plots for Quenching of Benzophenone Photoreduction by Biphenyl. 2 , V 0.054 M benzophenone 0.035 M benzophenone 0.02 M benzophenone 0.0075 M benzophenone 0 810 o I l l J 0-5 1.0 1.5 2.0 x 10’2 474-Chlorobipheny1_7 Stern-VOlmer Plots for Quenching Of Benzophenone Photoreduction by 4-Chlorobiphenyl 41 7 "’ Q 6 " r 5 P ‘ ’ ¢o C) 0.054 M benzophenone 3 3 - O O _. 0 9 0.035 M benzophenone 2 L ' ‘3 e 0.02 M benzophenone 1 /”' 0 0.0075 M benzophenone j 1 l 1 2 3 4 x 10' [fBiphenyl_7 Figure VI: Stern-VOlmer Plots for Quenching of Benzophenone Phosphorescence by Biphenyl. Z 4 3 _ .; 5 4 O , ' _O 0 2,. O , . ' e O 0.035 M benzophenone //¢fi3 o 0.025 M benzophenone 1 ' O 0.017 M benzophenone O 0.008 M benzophenone 1 l 1 1 2 3 x 10'3 lf4-methylbipheny147 Figure VII: Stern-Volmer Quenching of Benzophenone Phosphores- cence by 4-methylbiphenyl. 42 O 0.054 M benzophenone e 0.025 M benzophenone 0 0.0083 M benzophenone 1 1 1 I 0.5 1.0 1.5 2.0 x 10" £f3-Chlorobiphenyl_7 Figure VIII: Stern-Volmer Plots for Quenching of Benzophenone Photoreduction by 3-Chlorobiphenyl, 2 ¢ 3 ' .SL d> 2 L O 0.054 M benzophenone $ 0.035 M benzophenone l 9 0.021 M benzophenone l l 1 l .5 1.0 1.5 2.0 x 10‘ ZTQ-Chlorobiphenyl_7 Figure IX: Stern-Volmer Plots for Quenching of BenZOphenone Phosphorescence by 2-Chlorobiphenyl. l 43 o 0.054 M benzophenone, 2-chlorobipheny1 quencher a 0.054 M benzophenone, 2-methylbipheny1 quencher O 0.013 M benzophenone, 2-methy1biphenyl quencher [fQuencher_7 Figure x: Stern-Volmer Plots for Quenching of Benzophenone Photoreduction by 2-Chlorobipheny1, and Benzophenone Phosphorescence by 2-Methylbipheny1 44 0.0075 - 0.005 '- O 4-methylbiphenyl quencher (DIP 0.0025 0 biphenyl quencher 0.001 0.005 . 0.00025 1 L l 2 3 4 5 x 10"2 ZfBenZOphenone47 Figure XI: Plot of 1/S Versus BenZOphenone Concentration (Phosphorescence) 0.04 L O o 0 w l O 4-chlorobiphenyl quencher 0.026 l 9 3-chlorobiphenyl quencher S 0.02 O biphenyl quencher 0.016 0.010 0.006-— 0.002 W l I l J l 1 2 3 4 5 x 10‘2 ZfBenzophenone 7 Figure XII: Plot of l/S Versus BenZOphenone Concentration (Photoreduction) 45 ggthgfsubstituted compounds phosphorescing most strongly. Figures XIII-XV and Table IV compare the phosphorescence spectra of biphenyl and the chloro-, methyl-, and dimethyl- biphenyls. The presence of an orthgfgroup removes what little structure there is in the biphenyl spectrum and apparently shifts the whole spectrum to higher energy. The ggghgfchloro- and methyl- groups shift the km of phosphores- ax cence emission by about 400 cm"1 and the onset by about 600 cm-1 while the ortho-dimethyl shifts the A cm.1 and the onset by 1400 cm-1. This steric effect is by about 600 max consistent with those first reported by Lewis and Kasha. The pg£afsubstituents shift the emission to lower energy. Egrgfchloro- and methyl-groups produce a shift of about 600 cm-1 while the di-parafmethyl compound produces a shift of about 1280 cm-1. Metafsubstitution produces little energy change. Meta chloro- and methylbiphenyl are identical to biphenyl, while di-mgtafmethylbiphenyl shifts the spectrum about 600 cm.1 to lower energy. Under the low resolution conditions used, biphenyl phosphorescence shows vibrational structure, including a prominent progression of about 1400 1 cm- , but with only shoulders corresponding to the lower- frequency vibrational modes reported by Lim.51 The meta- and para-substituted compounds show this same progression. 46 Table III Absorbance of Biphenyls Compound Absorbance e Solvent biphenyl 2477 16700 heptane Z-Chlorobiphenyl 2410 8450 heptane 3-Chlorobipheny1 2480 16100 heptane 4-Chlorobiphenyl 2520 19200 heptane 2-Methylhipheny1a 2350 10500 ethanol 3-Methy1biphenyla 2490 16300 pentane 4-Methylbiphenyla 2530 19000 ethanol 2,2'-dimethy1bipheny1a 2270 6800 ethanol 3,3'-dimethylbipheny1a 2505 16100 pentane 4,4'-dimethylbiphenyla 2556 20500 ethanol a Value taken from reference 140 page 281. 47 .COeuomemp mamom wow usonm um pwusmmme " KM mHmmeOGMQ CH Gmhflmmmz 5‘ How pmumfla ucm>H0m mo “mono so wouqu n m mow woe owe woe ooe wee owe --- ooe HaguoEHon.e.e oow ooe Nee wwe wwe Nee ooe --- ooe emnuoseou.m.w owe ewe owe ooe --- ewm Hoe0o2eou.o.~ eoe wwe wwe oow wwe eee wee --- wee ewe0o21e owe oee wow ooe eee wwe --- wee Hoeuozuw wwe ewe wow --- ooe Hoeuozum owe eee www --- owm onoeeoeo-.~.~ eow wwe wwe Noe woe wee wwe oee wee ewe wow onoeeoue wee owe eee ewe wwe wwe eee ooe eom www ohoenoum wwe ooe wee owe wwe eee woe owe www onoenoum ooe wwe oee woe wwe wwe wwe wwe owe wwe woe wow Hoeonoam mcmxmnoaoho mcmummm mamxmnoaowoamnumz xmse x654 meK ummco ahcmnmwm wmaacwnmwm mo mocmomwuonmmonm >H wands 48 L 400 450 500 550 nm Figure XIII: Phosphorescence Spectra of Biphenyl and Methyl- biphenyls.(———0 Biphenyl, (---) 4-Methylblphenyl, (xxx) 2-Methylbiphenyl, (---) 3-Methylb1pheny1. .- v--‘-- l 1 l l 400 450 500 550 nm Figures XIV: Phosphorescence Spectra of Biphenyl and Chloro- biphenyls. (-——) Biphenyl, (---) 2-Chlorobipheny1, (xxx) 4-Chlorobipheny1, (°-°) 3-Chlorobiphenyl. 49 Figure XV: . . , wwe ... 314 338 386 450 530 nm Phosphorescence (top) and Fluorescence (bottom) Spectra of Dimethylbiphenyls. (———) 2,2'-Dimethy1- biphenyl, (-—-) 3,3'-Dimethylbiphenyl, (xxx) Biphenyl, (---) 4,4'-Dimethylbiphenyl. 50 Fluorescence Spectra of Biphenyls: Fluorescence spectra were measured at 250 in cyclohexane and methylcyclohexane. Table V lists the Amax of the biphenyls studied. Only slight changes are observable upon substitution, and all the spectra are essentially identical to that of biphenyl itself except for the two orthgfdisubstituted compounds. (See Figure XV). The spectrum of 2,2-dimethyl- biphenyl is lowered drastically compared to that of the other dimethylbiphenyls but shows the most structure. It is compared to the spectra of the other dimethyl compounds (which are characteristic of the other biphenyls) in Figure XV. Triplet EPR Spectra of Biphenyls: Triplet EPR spectra of biphenyl, the chlorobiphenyls and the six methylbiphenyls were measured at 9237 MHz in ethanol glass at 770K. Both Am = 2 and Am = 1 transitions were readily measurable. Table VI lists the zero-field parameters. In the case of the three chlorobiphenyls there are no significant differences. These similarities lead in fact to the possi- bility that the loss of chlorine might be occurring with the formation of biphenyl. This process is known to be particularly efficient for orthgfchlorobiphenyl at room temperature.142 Consequently the triplet lifetimes of the different chloro O O 143 derivatives were measured by monitoring both their phos- phorescence and ESR decay. The reported rp for biphenyl itself is 4 sec.52 The Tp for ortho-chlorobiphenyl was found to be 0.12 sec. The decay of meta-chlorobiphenyl 51 Table V Fluorescence Data for Biphenylsa Biphenyl Onsetb Amax Amax Methylcyclohexane Cyclohexane Biphenyl 295 296 320 628 320 624 2-Chloro 291 292 324 630 322 636 3-Chloro 300 300 320 636 322 638 4-Chloro 302 292 324 642 324 638 2-Methyl 310 292 328 640 320 630 3-Methyl 284 --- 334 656 4-Methy1 290 304 324 630 334 654 2,2'-Dimethyl 306 290 328 350 356 320 351 359 3,3'-Dimethy1 292 300 318 638 326 632 4,4'—Dimethy1 295 304 338 652 336 652 2,2'-Dichloro 284 --- 300 a Measured in nanometers bListed in order of solvent listed for Amax: measured at about 80% scale deflection. 52 consisted of two components with Tp values of 0.18 and 0.45 sec. The latter accounts for only 25% of the total intensity. Clearly different triplets for the different chlorobiphenyls are being observed in the phosphorescence experiments. However, the ESR signals for all three chlorobiphenyls decayed with the same 2-4 sec lifetime, indicating that biphenyl itself is responsible for most of the ESR signal. The zero-field parameters for the three methylbiphenyls and 4,4'-dimethylbipheny1 are essentially identical, although grthgfmethylbiphenyl displays a higher than usual E value. Of all the biphenyls studied only 2,2'-dimethyl- and 3,3'- dimethylbiphenyl yield two triplet ESR spectra. In the 3,3'- compound two sets of Am = l signals are apparent, independent of sample freezing rate. The 2,2'-compound also shows two quite distinct Am = 2 signals as well as two Am = l signals. These spectra are reproduced in Figures XVI-XVIII, while the ESR parameters for all the biphenyls are listed in Table VI. Under conditions in which the samples were frozen slowly the 2,2'-compound yielded largely one spectrum (Am = 2 at 1511 G). The line widths of the Am = l signals are broader for the 2- and 4-methy1 substituted biphenyls than for the 3-methyl- biphenyl, biphenyl or the chlorobiphenyls. The chlorobiphenyls and the 3-methylbipheny1 display linewidths identical to biphenyl itself. The linewidths of the Z-2,2'-dimethy1- biphenyl (see Discussion section for structure) are twice as wide as those of the other biphenyls. The average E 53 value (0.00456) for the two 3,3'-dimethylbiphenyl triplets is nearly that of the E value of 3-methy1biphenyl (0.00423). The fine structure constants were obtained by the use of the following equations:144 0*2 = (3/4) 1f52-4(ge)zhmin2_7 (17) 0*2 = (D2+3E2) (18) D = -(3/2)z (19) E = l/2(X-Y) (20) x = (1/6)6(gs)2453hx2-an2_7 (21) Y and Z are obtained from cyclic permutations of x,y, and 2. In the above equations 6=hv which at v=9237.5 MHz is 6.12104 -17 -39 x 10 erg.sec x MHz. (98)2 equals 1.3790 x 10 Mcyzergz/ gauss4. H is the observed field signal measured in gauss. 54 Table VI Observed EPR Resonances and ZFS Parameters of Phosphorescent Biphenylsa Biphenyl D E *calc Dfirobs Biphenyl 0.1089 0.00349 0.1090 0.1084 2—Methyl 0.1067 0.00698 0.1073 0.1054 3-Methy1 0.1077 0.00423 0.1079 0.1080 4-Methyl 0.1067 0.00365 0.1069 0.1051 4,4'-Dimethyl 0.1062 0.00369 0.1064 0.1046 E-3,3'-Dimethyl 0.1067 0.00335 0.1068 0.1069 Z-3,3'-Dimethyl 0.1067 0.00700 0.1073 0.1069 E-2,2'-Dimethy1 0.1068 0.00603 0.1051 0.1051 Z-2,2-Dimethyl 0.1211 0.00850 0.1237 0.1280 2-Chloro 0.1080 0.00348 0.1090 0.1083 3-Chloro 0.1092 0.00355 0.1094 0.1084 4-Chloro 0.1088 0.00357 0.1090 0.1076 a The spectra of the methylbiphenyls were recorded on a Varian E-4 spectrometer and the spectra of the chloro- biphenyls were recorded on a Varian X-band spectrometer. 55 Table VI (Con't) Observed EPR Resonances and ZFS Parameters of Phosphorescent Biphenylsa J . C C C X Biphenyl Hmin Hx Hy Hz Y Z . 2704' 2598 2134 Biphenyl 1506 3779 3897 4463 0.0328 0,0393 0.0725 2164 2-M h 1514 2797 2534 . . 0.0715 et yl . 3689 3926 4442 0 0273 0 0413 . - ‘ 2142 3-Meth 1 1507 2719 2594 . 0.0403 0.0718 y 3758 3905 4448 0 0318 4-Methyl 1511 2719 2510 2166 0.0320 0.0394 0.0723 3765 3891 4442 4,4'-DImethy1 1516 2732* 2627 2139 0.0315 0.0389 0.0708 3758 3889 4423 E-3,3'-Dimethyl 1510 2717 2616 2153 0.0322 0.0382 0.0711 3770 3885 4433 Z-3,3'-Dimethyl 1510 2756 2583 2153 0.0298 0.0438 0.0711 3727 3922 4431 E-2,2'-Dimethyl 1511 2729 2582 2163 0.0292 0.0413 0.0712 3693 3924 4444 Z-2,2-Dimethy1 1446 2793 2496 1982 0.0299 0.0469 0.0807 3760 4019 4583 2-Chloro 1502 2701 2595 2130 0.0330 0.0399 0.0726 3776 3895 4461 3-Chloro 1502 2701 2592 2125 0.0329 0.0400 0.0728 3774 3895 4462 4-Ch1°ro 1504 2701 2592 2133 0.0327 0.0498 0.0725 3769 3891 4459 b Observed signal in gauss, measured half—way between top and bottom of curve. cObserved signal in gauss, measured half-way between curve. Figure XVII: 56 ' F—fi l 1446 11 G 1511 Figure XVI: Am - 2 Signals for 2,2'-Dimethylbiphenyl line). (solid line) and 3,3'-dimethylbiphenyl (dotted Field measured in gauss. l 1982 1——1 I l 22 G 2153 2163 Z Signals for 2,2'-Dimethylbiphenyl (top) and 3,3'-Dimethylbiphenyl (bottom). in gauss. Field measured 57 .mmsmm no cmusmmmfi pamflm .AEouuonv Hmsosmflnamnmewpl.m.m cam Amouv Hmcmnmfibamnuofioon.~.m How mamcmom M can x mth mmBN mNhN mHhN mem NmmN . _ . . _ _ "HHH>x ousoem mmvm _ DISCUSSION The goal of this work was to find the minimum sized ggthgfsubstituents necessary to force triplet biphenyl out of planarity and to then construct a potential energy diagram which would describe: (1) the ESR spectra of the chloro and methylbiphenyls, (2) the opposite effects of REESE? and para- substituents on the energies of both Sd+Si absorption and T*+SO emission, and (3) the Opposite effects of EEEEQI and para-substituents on the rate constants for energy transfer from triplet benzophenone to biphenyl. Planarity of the Biphenyl Triplet: Zero-field spin-spin interactions should be strongly dependent on the degree of conjugation and thus coplanarity of the two rings in triplet biphenyl.50 Yet, since the resonance energy varies with the cos2 of the angle of twist145’ slight changes from coplanarity might not show measurable effects. In fact a twist angle of 450 should destroy approxi- 146 The mately 50% of the resonance energy of the molecule. very nearly identical D values for biphenyl, the monomethyl- biphenyls, 4,4'-dimethy1biphenyl, and the two 3,3'-dimethyl- biphenyls indicate that all seven triplets retain the same planar geometry. Since both 2,2'- and 3,3'-dimethylbiphenyl can exist in two conformations, as illustrated below, the two triplet 58 (I)_ 59 species observed for each are most reasonably attributed to the separate conformers. It would be expected that the two conformers of 3,3'-dimethylbiphenyl would produce triplets with the same D value and with E values just different enough to yield distinguishable Am = 1 signals, but not different enough to yield two different Am = 2 signals. Two groups on the same side of the long molecular axis should produce a significant increase in anisotropy, so Z-ZZ E-QZ Z-3,3 is assigned the larger (0.007 cm-l) E value. It is interesting that an average of the two E values of the two triplets produced from 3,3'-dimethylbiphenyl (0.00480) is nearly that of 3-methylbiphenyl (0.00423). Interestingly, the two conformers of 2,2'-dimethyl- biphenyl produce triplets with distinctly different D and E values. The conformer with the lower D value has been assigned as E-2,2'-dimethylbiphenyl since the two gfmethyl, o'-hydrogen interactions should be similar to the o-methyl, ‘gf-hydrogen: o-hydrogen, g'-hydrogen interactions of 60 2—methylbiphenyl. The gfmethyl, g'-methyl interaction should be the strongest interaction and thus the higher D value has been assigned as Z-2,2. Of all the biphenyls studied only Z-2,2 displays a large enough D value that it can be deduced to be non-planar. It can be concluded then that the repulsive nonbonded interactions between an orthgfchlorine or grthgfmethyl and an grthgf—hydrogen are not sufficient to cause triplet biphenyl to lose the conjugation stabilization afforded by planarity, at least not enough to produce measurable changes in the ESR. But these interactions are sufficient to produce measurable effects on the quenching rate constants, absorption, and emission of these compounds. The D value of 147 benzene is 0.159 and allows a rough estimate of the angle of twist of triplet Z-2,2 of at least 20°. Effects of Substituents on the Triplet: The chlorobiphenyl ESR decay studies obtained by Mary May143 clearly indicate that the signals are produced by biphenyl itself. Apparently chlorine is being ejected from the molecule during the irradiation to produce the triplet, although such is not observed during the phosphorescence studies. Since no useful ESR data could be obtained from the chlorobiphenyls, the methylbiphenyls were studied. The moderately lower D values for the methyl substituted biphenyls coupled with the observed broadened linewidths of the Am = l signals for the ortho- and para-methylsubstituted 61 biphenyls indicate that hyperfine interactions between the electron spin and the nuclear spin of the benzylic hydrogens are occurring. It is interesting to note that the X and Y signals of the Z-2,2 triplet are twice as broad as those of the other biphenyls. This is probably due to the enhancement of spin density at the methyl-substituted grthg carbons of this nonplanar, less conjugated triplet. The decrease in the energies of the lA+1La (SO+S*) and 3La+1A (T*+S) transitions caused by para-chlorosubstitution is a normal inductive substituent effect on the La states.141 The decrease caused by the para-methyl group must be a combina- tion of inductive and hyperconjugative effects. It is 1 interesting that the 600 cm- shift in the phosphorescence spectrum shown by the para-chloro and methyl substituents and the 1280 cm-1 shift caused by di-para-methylbiphenyl are 1 very close to the 700 cm- shift reported for the triplet energy of chlorobenzene, the 500 cm-1 shift for toluene, and 13 the 1300 cm-1 shift for para-xylene relative to benzene. Effect of Meta-Substitution: A meta-chlorine or methyl substituent produces no change in the energies of absorption or emission. The di—mgtgf methylbiphenyl shows a slight red-shift in absorption but no change in the extinction coefficient and a slight shift in emission. Moreover, the metafchlorine does not shorten the phosphorescence lifetime of biphenyl nearly as much as does an ortho-chlorine, and the ESR line widths of the 62 meta-substituted biphenyls are identical to those of biphenyl itself. These results are interesting in the light of Mispelter's95 recent evidence that there is negligible free spin at the meta-position of triplet biphenyl. Metafchloro- biphenyl is a better quencher of triplet benzophenone than biphenyl itself. Very small changes in triplet energy can have large effects on observed rates of reversible, approxi- mately thermoneutral, energy transfer. Since commercially available 3-chlorobiphenyl is quite impure, it is possible that residual impurities enhanced the quenching efficiency. The second component observed in the lifetime studies may be due to this impurity. Steric Effect of Ortho-Substituents: It is relatively easy to rationalize the higher energy phosphorescence of the orthgfsubstituted biphenyls relative to biphenyl. Both chlorine and methyl groups are bulkier than hydrogen and therefore introduce a larger steric barrier to planarity than exists in biphenyl alone. This steric destabilization should be larger in the excited state than in the ground state since the shorter central bond in excited biphenyl bringsthe methyl.or chlorine closer to an gf-hydrogen. The grthgfsubstituent increases the energy difference between the planar conformation of the ground and triplet states. Since phosphorescence involves just such a transition, its energy is increased. 63 It is interesting that of all the biphenyls studied only 2,2'-dimethy1biphenyl shows structure in the fluores- cence spectrum. 2,2'-dichlorobiphenyl shows reduced fluorescence, as do all the orthg-substituted biphenyls, but no real structure. It is possible that this structure is due to the two conformers of the dimethylbiphenyl. Effect of Substituents on Ground State Biphenyl: Preconceived concepts about what grthg-groups should do to biphenyl's ground state can easily lead one into error. For example, one might expect that 2,2'-dibromo- and 2,2'- dichlorobiphenyl would prefer the trangfconformation. X-ray and other studies have indicated that these molecules prefer the Sigfconfiguration, at least in the solid. London attractive forces have been involked to explain this prefer- ence. Unanue and Bothorel148 have estimated the angle of twist and the Van der Waals distance beteen the orthg groups using a Rayleigh light scattering technique. These data are listed in Table VII. Interestingly they predict from their observed data on 2,2'-dimethylbiphenyl and the results on 2-methylbiphenyl and 2,2',4,4',6,6'-hexamethylbiphenyl that the trans and gig conformers of 2,2'-dimethylbiphenyl are equally likely to exist. This same prediction is also true for 2,2'-dichloro- biphenyl albeit the angle of twist is greater. This result 140 is in agreement with that of Suzuki's who indicates that 64 Table VII Observed Angles of Twist and Van der Waal's Radii for Biphenyls Bi hen 1 Observed "Normal"(b) p y (a) o ..O o "2 angle radllA angle radii biphenylc 31d 2.14 43°3o' 2.40 4-methy1-° 34 2.18 43°30' 2.40 4-bromo-c 22° 1.97 --- --- 2-methyl-C 46°30'(58)e 2.45 72°30' 3.20 2-ch1oro-° 48°30' 2.52 66° 3.15 2,2'-dimethyl-C cis- 498(800)e 2.50 842 4.00 trEfiEL 48 30' 2.52 72 30' 3.20 2,2',4,4',6,6'-° 47° 2.45 --— --- hexamethyl- 2,2'-dichloro- o o o cis- 64 (74 )g 3.07 98 30' 3.72 trEHE- 600 2.90 66° 3.06 2,2'-dichloro- o benzidinef 72 2,2'-dimethyl- o benzidineg 86 aAngle of twist between rings bDue to steric effect only cReference 148 d e Reference, 149 fReference, 150 9References 151, 160 O°(crysta1), 45°(vapor), 20-30°(solution) 65 2,2'-dimethylbiphenyl is mostly in the trans conformer, but that some gig conformer is probably present. Suzuki's conclusion is based on the similarity of the UV spectra of 2,2'-dimethylbiphenyl and 2,6-dimethylbiphenyl gig. the inflection at 227 mu due to the vestigal A band. The ESR results reported here clearly indicate that both conformers are present. It is interesting that the methyl groups have so much less net effect than the chloro groups. Quite obviously the angle of twist and compression of the C-H or C-R (orth2)bond, the bending of the orthgfhydrogens and halo and methyl groups away from one another, deformation (stretching) of the inter- annular bond, and the deformation of the benzene rings are in a delicate balance. In the excited state, this balance is even more delicate. The planar excited triplet then may be represented somewhat as indicated by Westheimer152 for the transition state in the racemization of optically active biphenyls. 66 Distortion of the Triplet as Evidenced by the Quenching Rates: The ESR data indicates that 2-chloro and 2-methylbiphenyl as well as 4-chloro- and 4—methylbiphenyl are planar in the triplet state. Yet the orthg-substituted compounds are poorer quenchers than biphenyl and the two parafsubstituted compounds do not approach a quenching constant near that of the diffusion controlled quenching rate. These results indicate that even for the 4-chlorobiphenyl good overlap between the n,“ orbitals of the biphenyl and the n,n orbitals of the benzophenone can not be achieved. Implicit in this conclusion is that non- vertical energy-transfer must be occurring even in the para- substituted compounds and thus the O-O band for phosphores- cence and that of the S+T* absorption should not coincide. Since greater geometric changes must occur in the 933297 substituted biphenyls during the energy-transfer process the observed quenching rates are lower. It is interesting that the smaller than predicted steric effect of the methyl groups in the ground state is carried over to the excited state. The orthgfmethyl groups has no where near the effect of the grthgfchloro group on the quenching rate. The para- methyl group does not stabilize the triplet as well as the ara- chloro group. Triplet Energy of the Biphenyls: The eight-fold increase in the forward rate constant for energy transfer from triplet benzophenone to biphenyl caused by para-chlorine substitution must reflect a decrease in the 67 triplet energy of biphenyl. Since the triplet energy of biphenyl has been estimated as 68.5 kcal/mole,9 the triplet energy of 4-chlorobiphenyl can be estimated as 67 kcal/mole. The para-chlorine presumably produces no change in the shape of either the ground or the excited state potential but lowers the excited state by 1.5-2 kilocalories relative to the ground state, independent of the angle of twist between the rings. The one and a half-fold increase in the forward rate constant observed for pagafmethylbiphenyl correlates with a triplet energy of 68.2 kcal/mole. Attempts to estimate the triplet energy of the QEEEEI substituted biphenyls is not as fruitful. The orthgfgroup changes the ground state potential by producing a larger barrier to rotation and therefore a more twisted minimum. In the excited state this interaction broadens the potential well. Construction of the Potential Energy Diagram: The potential energy diagram is depicted in Figure XX. The points of highest energy in the ground state and excited state potential wells indicate the difference in energy between the ground and excited states in benzene (approximately 85 kcal/mole), toluene, or xylene. The excited state potential well is deeper than that of the ground state, since the 1-1' bond has more double bond character (higher bond order). The differences between the ground and excited state potential wells at 00 and at about 250 correspond to the values 68 determined by the spectrosc0pic and nonspectroscopic T*+S transitions in biphenyl9 (solid line). The dotted and dashed lines represent the estimated changes caused in the potential wells by the incorporation of ggghg-substituents. The dotted line indicates the presumed distortion caused by a mono-ggphg- substituent. The barrier to rotation is increased in the ground state and the potential well is broadened in the excited state. Placement of two groups in the ggphgfposition (dashed line) increases the barrier to rotation even more in the gound state and the excited state now shows that two conformationally distinct triplets are possible. The ESR data on the 2,2'— dimethylbiphenyl indicates that a slight activation energy barrier is established for the interconversion of the two conformers. Of the two possible conformations in the excited state of the di-ggghgfsubstituted biphenyl, one probably has a lower energy well than the other. For a more complete description of changes in potential wells accompanied with steric effects the reader is referred to Jaffe and Orchin.153 Indications for Future Research: The following studies would further elucidate the steric effects involved in excited state biphenyls: (l) The ESR and low temperature NMR studies of 2,2'- di(trifluoromethyl)-6,6'-difluorobipheny1 would be quite intriguing. In the Z conformation the grthgffluorine should split the grghg'-fluorine and in the E conformation it would be split by 69 85- 65* Figure XIX Potential Energy Diagram for Biphenyls (———) Biphenyl, (---) monosubstituted ortho- biphenyls, (---) disubstituted ortho-biphenyls. (2) (3) 70 the trifluoromethyl fluorines. The ESR spectrum might be quite complex because of the hyperfine fluorine splittings. The quenching and ESR studies with one orpha- substituent and groups in the megafposition of biphenyl should give some idea as to how important "buttressing" effects are in the excited states. It would be interesting to see the effect of an ngf butylgroup on the triplet state. The ESR of a series of metafsubstituted biphenyls to determine if the E values of the two conformers from disubstituted biphenyls are really additive would be appropriate. The singlet and triplet lifetimes of the biphenyls would be interesting to determine. Hopefully the disubstituted materials would show two different decays indicative of the two possible conformers. AZIDOALKYL PHENYL KETONES RESULTS Part II Three azido phenyl ketones were prepared by an 5N2 reaction of sodium azide on the corresponding haloketone or ketal. The efficiencies with which y,0 and e-azidoalkyl phenyl ketones undergo the Type II photochemical reaction were measured in benzene. As indicated in Scheme II (Introduction) a large number of products might be formed upon irradiation of these ketones, yet the VPC traces of irradiated azido ketones are relatively simple. During irradiation benzene solutions of y-azidobutyrophenone turn dark yellow or light orange. Solutions of 6-azidovalerophenone turn only a pale yellow and solutions of irradiated e-azido— phenone remain colorless. Type II quantum yields of y-azido- butyrophenone exhibit a wavelength effect, concentration effect, and vary with irradiation time. Type II quantum yields of o-azidovalerophenone exhibit a wavelength effect, and vary with irradiation time. Type II quantum yields of e-azidohexanOphenone behave normally. Identification of Photoproducts of Azidoalkyl Phenyl Ketones: (a) From y-azidobutyroPhenone: The VPC trace of photolyzed y-azidobutyrophenone is 71 72 reproduced in Figure (XX). Peaks I and IV are the standards tetradecane and octadecane, respectively. Peak VII is the parent ketone and peaks II, III, V, and VI represent the photoproducts. Attempts to isolate all these products by preparative VPC proved futile. Passage of irradiated solution through a preparative VPC containing a thermal detector gave only 2-phenyl—A1-pyrroline(PPRL) and acetophenone, while an unirradiated sample gave only PPRL. The PPRL was identified by comparing the VPC retention time of the material obtained from the preparative VPC with that of a pure sample (prepared by A. E. Kemppainen). The NMR and mass spectra of the pure PPRL and that of the isolated material were identical. Aceto- phenone was identified by its VPC retention time compared to that of a pure sample. It was important to establish whether peaks V and VI were the cyclobutanols or nitrene-derived products. Since other methods of identification proved unsuccessful, the.materials were analyzed by GC/mass spectrographic techniques. The data obtained are presented in Table VIa. Table VIa GC/Mass Spectral Data for y-Azidobutyrophenone Compound Peak, m/e 2-phenylpyrrole (Peak VI) 143 2-phenyl-A1-pyrroline (Peak III) 145 y-azidobutyrophenone (Peak VII) 161 (189-28) 73 elaou paw Huaou .mcoconmonhusooofiudlx commaouocm mo momma om> 2H2 0m "xx musmflm 5 HH> A H> >H ‘ AH fl esuodsea 74 2H2 mm H> HIHOO mcocmnmoumam>0©HNMIw Umuwaouozm mo momma om> ”Hxx musmom Om 9 Q q - >H HHH -‘ HH L10 asuodsea 75 The GC/mass spectral data do not completely rule out the possibility that peaks V and VI are the cyclobutanols, since conceivably the cyclobutanol could loose nitrogen and water to give a parent peak of 143. An irradiated sample of Y-azidobutyrophenone(AZBP) was placed on an alumina column and eluted with 20% ethyl acetate benzene. Peak VI was eluted as a brown oil. This material was sublimed and resublimed. The physical properties and spectral data are consistent with this material being 2-phenylpyrrole. A 40% chemical yield of 2-phenylpyrrole was realized. Peak V was never eluted even after pure methanol was used as the elutant. It is possible that this material is the oxazirane (see Discussion) precursor to the 2-phenyl pyrrole. Peak V does not appear in the GC/mass spectral trace either. Peak V is also quite photoinert since prolonged irradiation caused peak VI to disappear while peak V neither decreased nor increased. The GC/mass spectrum of peak VII is identical to the mass Spectrum obtained for the unirradiated azidoketone. That peak VII is the parent ketone (AZBP) was further confirmed by isolation of the AZBP from an irradiated sample by column chromatography. Elution of the parent ketone from an alumina column was effected with hexane. The IR and NMR of this material were identical to that of the unirradiated material. A brown oil eluted from the alumina column subsequent to the 2-phenylpyrrole shows azide, carbonyl, and either NH or OH absorbances in the IR. The NMR of the material is essentially 76 that of the AZBP. It shows no VPC trace and is assumed to be polymers derived from AZBP, 2-phenylpyrrole, or y-iminobutyro- phenone. During the photolysis of AZBP in cyclohexane a yellow oil collects on the sides and bottom of the tube. This material turns brown when exposed to the air and IR and NMR data are identical to that of the brown oil collected from the chromatOgraphic studies. (b) From G-azidovalerophenone: The VPC trace of photolyzed d—azidovalerophenone (AZVP) is reproduced in Figure (XXI). Peaks I and III are the standards tetradecane and heptadecane respectively. Peak II was identified as acetophenone by comparing its retention time to that of a pure sample. To identify the other peaks, an irradiated sample of AZVP was subjected to GC/mass spectral analysis. The results are indicated in Table VIIa. Table VIIa GC/Mass Spectral Data for 6-Azidovalerophenone Compound Parent Peak 2-phenyl-3,4,5,6- tetrahydropyridine (V) 159 6-azidovaler0phenone (VI) 175 (203-28) VPC Peak IV 173 Peak IV appeared in the VPC trace before AZVP was irradiated and it neither increased nor decreased after irradiation. Its identity remains unknown. 2-Phenyl-3,4,5,6-tetrahydropyridine was identified by its GC/mass spectrum. The GC/mass spectrum of peak VI was identical to the mass spectrum of unirradiated 77 AZVP. It is assumed that peak VI is AZVP since AZBP was isolated by column chromatography. (c) From e-azidohexanophenone: The VPC trace of irradiated e-azidohexanophenone (AZHP) shows only acetophenone on Col-3. Parent ketone gives no signal. On Col-4 parent ketone and peaks presumed to be cyclobutanols can be detected. These cyclobutanols have one half the area of the acetophenone peak and produce a signal in the same general area that the cyclobutanols from valerophenone and N-methyl-4-methyl-4-benzoyl piperidine are observed. Quantum Yields: Quantum yields for acetophenone and other product forma- tion were measured at 366 and 313 nm by concurrently irradia— ting degassed solutions of ketone in benzene containing various additives. ValerOphenone actinometers of identical optical density as the studied ketone were present during the entire irradiation period. Per-cent conversions in the valerOphenone samples were no more than 15%. Per-cent conversions in the azidoketone samples were usually kept at 5% or below except in the case of AZBP where per-cent conversions were usually about 10%. Product to standard ratios of photolyzed ketone and valerophenone were measured by VPC. The quantum yields for AZBP and AZVP were measured in cyclohexane following the procedure described for the studies in benzene. 78 Wavelength Effects: At 313 nm the extinction coefficient of a 0.07 M solution of acetophenone is 4230 while the extinction coefficient of a 0.07 M solution of butyl azide is 7105. At 366 nm the absorbance of the azide group is negligible while that of the phenyl ketone is about 10. The photolysis of AZBP at 313 nm where the azide group is absorbing about 20% of the incident light gives interesting results.. The quantum yield for disappearance of ketone is increased by a factor of two relative to 366 nm irradiation. This same increase in quantum yield is observed for 2-phenyl- pyrrole and peak V. The most intriguing result is observed for the acetophenone quantum yield. Its initial value at 313 nm is equal to that observed at 366 nm, but at 313 nm the quantum yield increases with irradiation time. These results are depicted in figures XXII and XXIII. In contrast to the behavior of the acetOphenone quantum yield for AZBP, the acetophenone quantum yield for AZVP at 313 nm stays constant with irradiation time but is slightly lower than observed at 366 nm (0.167 versus 0.195, respectively). Since it appeared that strange occurrences might be happening when light is concurrently absorbed by the carbonyl and azide moieties, all further work was performed at 366 nm. Variation of Quantum Yields with Per-cent Conversion: If quencher molecules are formed as a result of irradia- tion, the Type II quantum yield can decrease.60 Since the O 0 9 O 79 Acetophenone 2-Phenylpyrrole and peak V 2-Pheny1-A1-pyrroline y-Azidobuterphenone .075. - 0.0075 0.60 L . - 0.0060 g 0.45 . 0.0045 -H w E g 0.30. 0.0030 0' 0.15r 3 0.015 e o o 1e 1 J 1 20 40 60 Figure XXII: % Conversion Plot of quantum yields versus % conversion of y-Azidobutyrophenone at 313 nm (scale on left is for disappearance of ketone and 2- Phenylpyrrole and peak V; scale on right is for acetophenone and 2-Phenyl-A1-pyrroline. 80 Acetophenone 2-Phenylpyrrole and peak V 2-Phenyl-A1-pyrroline 6-Azidobutyrophenone 0.32. 2'2 :JL1r_______ 0.28t I3 0, 0.24_ «4 g 0.20: g 0.16“ (U .‘3 0-03- «0.004 X C O G— 0-04 fi‘-~1§-~‘~“‘-—4}1F‘-__-;%0.002 6ND. L J» 1 O 10 20 30 Figure XXIII: % Conversion Plot of quantum yield versus % conversion at 366 nm (scale on left is for disappearance of ketone, 2-Phenylpyrrole and peak V, and 2-Phenyl-A1-pyrroline; scale on right is for acetophenone. 81 azidoalkyl phenyl ketones do produce products which can act as quenchers, a check of Type II quantum yield with irradia- tion time in benzene was made. The actually observed decreases of Type II quantum yield for AZBP and AZVP with irradiation time are depicted in Figures XXIV, XXV. Certainly the 2-phenylpyrrole would be expected to act as a quencher because of the low triplet energies exhibited 175 Since amines quench carbonyl triplets at about a diffusion-controlled rate89, by heterocyclic aromatic molecules. the cyclic imines formed in the photolyses of AZBP and AZVP might also be expected to act as quenchers. To check this notion 2-(4-pff1uorophenyl)-A1-pyrroline was used to quench the Type II reaction from buterphenone; a quenching constant (Stern-Volmer slope) of 264 M”1 was obtained. The olefinic azides produced from the Type II reaction of the azido ketones would also be expected to act as quenchers. The decrease in Type II quantum yield with increasing conversion can also occur if products are formed which can absorb incident light. The hypothetical iminoketones would absorb light and the observed decrease of Type II quantum yield may be enhanced slightly by the latter effect. Concentration Effect: Normally Type II quantum yields increase with an increase in ketone concentration.4 However, since the azide moiety can 115 Type II quantum yields of the azido ketones act as a quencher might be expected to decrease with increasing ketone concentra- tion. The variation 0f Type II quantum yield with ketone 82 concentration for AZBP is indicated in Figure XXVI. The effect was almost negligible for AZVP and only somewhat larger for AZBP. The magnitude of this intermolecular quenching of triplet carbonyl by azide was measured by quenching the Type II reaction from butyrophenone. The measured ktT value was 10 M-l. Since 0.07 M ketone seemed to minimize both the concentration effect and variation with per-cent conversion effect, all further work was performed at this ketone concen- tration. Quenching Studies: Stern-Volmer quenching lepes for the quenching of aceto- phenone formation were obtained by 366 nm photolysis of 0.07 M azidoketone solutions containing varying concentrations of l-methylnaphthalene in benzene. Per-cent conversions were maintained as low as possible and the slopes were linear. A Stern-Volmer plot was also obtained for the quenching of 2-phenylpyrrole and peak V from AZBP. The slope of this plot was found to be similar to the slope of the plot obtained for acetophenone formation. The Stern-Vblmer plots are depicted in Figures XXVII and XXVIII. Intersystem Crossing Yields: Intersystem crossing yields were determined by irradiating at 366 nm 0.07 M ketone solutions containing varying concentra- tions of gigfpiperylene concurrently with a solution of 0.07 M acetophenone containing gisfpiperylene. Plots of reciprocal quantum yield versus cis-piperylene concentration were linear. 83 There was some concern that in these studies the nitrene might add to the piperylene. However, photolyzed solutions of AZBP did not turn yellow in the presence of piperylene. No anomalous peaks were seen in the GC traces and the data was 176 has indicated repeatable and internally consistent. Lewis that triplet azide does not isomerize piperylene nor add to it. The plots obtained are shown in Figure XXIX. The ¢isc for y-azidobutyrophenone is 0.80 while the ¢isc of 0-azido— valerophenone is 0.98. Corrections Applied to Quantum Yields and Quenching Values: In order to calculate the GI value for the azido group, the behavior of the azido ketones will be compared to valero- phenone.60 Thus it was necessary to correct the observed quantum yelds and ktT values for the conversion and concen- tration effects observed for AZBP and AZVP. No corrections were necessary for the observed AZHP values. The corrected and measured quantum yields and ktr values are listed in Table VIII. The conversion effect was removed for AZBP and AZVP with the aid of the plots in Figures XXIV and XXV. The measured quantum yield of a 0.07 M AZVP benzene solution irradiated at 366 nm at three different per-cent conversions was extrapolated to zero per-cent conversion. It was assumed that during the pyridine and quenching studies, AZVP would behave proportionally the same as in benzene. Thus the measured 9m and ktT values ax at a particular per-cent conversion were extrapolated to 0% conversion using the quantum yield study in benzene as the . 168 . . reference ratio. No per-cent conver51on correction was 0.25 0.2" '0 F4 .3 0.15- >4 E C 10 a 0.1?" Figure XXIV: 0.006 0.005 0.004 I I 84 0 0.05 M ketone O 0.1 M ketone O 0.07 M ketone J l l 10 15 20 % AcetOphenone Formation Plot of Type II quantum yield versus aceto- phenone formation at 366 nm of G-azido- valerOphenone. O 0.05 M ketone $ 0.07 M ketone O 0.1 M ketone 0.002 Quantum Yield 0.003 L—er—ELG - t l l 1 Figure XXV: 0.5 1.0 1.5 % Acetophenone Formation .Plot of Type II quantum yield versus % aceto- phenone formation at 366 nm for y-azidobutyro- phenone. 85 0.0085 P 0.0075 - 0.0065 0.0055 antum Qu. 0.0045 Yield 0.0035 0.0025 0.0015 F l 1 1 I 0.025 0.05 0.075 0.10 [II-Azidobutyrophenone47 Figure XXVI: Plot of Type II Quantum Yield Versus 1 y-azidobutyrophenone_7 Irradiated at 366 nm. '0 1.5 ~ O Butyl Azide 1,0 3 2-(pffluorophenyl)-A'-pyrroline l 1 g 1 3 5 7 x 10-2 x 10'3 Figure XXVII: Stern-Volmer Quenching Plots of Buterphenone by Butyl Azide and 2—(Effluorophenyl)-A1—pyrroline. 86 (3 Acetophenone from y-Azidobutyrophenone 6 AcetOphenone from e-AzidohexanOphenone 2-Phenylpyrrole from y-Azidobutyrophenone . Acetophenone from o-Azidovalerophenone l 1 1 0° 0.1 0.2 0.3 _2 90 0.5 1.0 1.5 x 10 [fl-Methylnaphthalene47 Figure XXVIII: Stern-Volmer Plots for the Azidoketones at 366nm. 87 CD y-Azidobutyrophenone 6 S-Azidovalerophenone l I l l 5 15 25 35 1/17Piperylene_7 Figure XXIX: Sensitization Plots of y—Azidobutyrophenone and G-Azidovalerophenone. 88 applied to values measured for 0.07 M AZBP solutions since the quantum yield does not change with per-cent conversion. Since the per-cent conversion slopes for the three different concentrations of AZVP studied all extroplate to about the same value at 0% conversion, no correction for a concentration effect was applied. The per-cent conversion plots for different concentrations of AZBP do not extrapolate to the same value at 0% conversion and thus a plot of ketone concentration versus quantum yield (Figure XXVI) was constructed. All the observed values (4, ktT, ¢max) for AZBP at 0.07 M ketone concentration were corrected by extrapolation to zero ketone concentration. In essence the ktt, 0, and ¢max values were multiplied by a factor of 1.73 (Figure XXVII). Since Wagner and Kemppainen6o have indicated that phenyl ketones produce cyclobutanols with quantum yields that average 15% of the observed maximum Type II quantum yields, 15% of the maximum Type II quantum yield for AZVP and AZBP was assumed to be equal the cyclobutanol quantum yield for these ketones. It is assumed that the cyclobutanols formed are either decomposing under the VPC conditions or have the same retention time as the parent ketone. Calculation of kr Values: The quantum yield for the Type II reaction can be written as a product of probabilities as shown in equation 21 or 22. 4 = ¢ ¢ (21) isc¢Br p 89 _ obs obs .. 4—kr t .iscpp (22) Rearrangement of this equation gives the following expression obs, for kr . kobs_ 4 obs max (23) r obs r - obs t Pp¢isc t ¢isc In W I The use of this equation requires that 4m 4, and ktI all be ax' measured at the same per-cent conversion.4 The observed life- time, t, was determined from the Stern-Volmer plot, where the slope is equal to ktT. Kt for naphthalene and 1-methyl- naphthalene was assumed to equal 5 x 109.32 The value for the probability of the biradical to go on to product (PP) was determined from the pyridine studies by dividing 4max into 4.4 The quantum yields and intersystem crossing yields (418C) were determined as previously described. The kr, 1/1, and Pp values obtained from equation 23 using the corrected quantum yields and ktT values are listed in Table IX. Calculation of Rates of Energy Transfer: Once kr is known, the ke values for energy transfer from t triplet carbonyl to the azide group are easily calculable from equation 24 (see mechanism in DISCUSSION section). 1/1 = kd + kr + ket + kq£_Qp;7 + kt£_RN3;7 (24) Rd for similar type ketones is on the order of 105 sec.1 and 60 can be ignored. Even though k is about diffusion controlled, t its effective quenching rate depends on the concentration of formed products. At low conversions (<10%), kqépr_7'will be 90 less than 107 sec.1 at 0.07 M ketone concentration. Kt for azide quenching has been measured in this work to be about 8 -1 10 sec . At 0.07 M ketone concentration, k éfRN3_7 should t have an effective quenching rate less than 107 sec-l. Thus qupr 7 and ktszN347 should add only small contributions to the measured triplet decay rates. The calculated ket values are listed in Table IX. .mm.o mo pamoa Educmsv HocmusnoHoao .em.o mo maocmnmoumod “Om Gama» Educmso «mcoumx z H.o so consummz x .omHm um omusmmmz n .mo.H umoEHm we mcoumepwnmnw mucom msHm> pmfidnmd a .mnucoe Hmum>mm uoumnoowummu so mcfluuom won own pace meEmm 30Ham> co cousmmmz n .meHHo Eoum pmumasoamu m .coflumuucmocoo mcouwx z H.o um pmudmmmz .pmcwmano mnam> ummnmwn .cooumuucwocoo mcoumx z oo.o um consume: 4 .cooumuucmocoo mwouwx z mo.o um omusmmoz .mcmxmonoxo CH consmmmz o .mowosum cowumNfluHmcmm Eoum .uxmu cw omnouommo mm pmuoouuow mum m>N< new mmN< mom mwSHm> nonuo HH< .moaam> Um gnome Hmsuom who A o no mosam>m wiemé oseoo xxwm.oo In: In: exo.Ho Amwo.oo Amo.oo oxem.oo Ammo mmwd now.o owH.o AHoHo m“ In: (In ~o.o wo.o moeo.o Awmo.oo mm.o moH.o Ammo HHH m>N< newo oweooo gamma .om.o mao.o moo.o om.o mmoo.o Aenoo.oomao.o mwoo.o Amaom+ofl mmus mop mHouuum ocoEw omw Hosnmo H>mmum.o smog o e e o e HHe HHe wx mcoumx as com um wmumwpmuuH cowumnucmocoo ocoumx z oo.o um pmnsmmoz monoumx Opwnd How mama HHH> OHQMB 92 oe.o mooV em.o em.o oo.a mmud oo.o om.o oa.o me.o ~.m m>ud om.o o.m mono o.m om.o mmNd mm 04m oa x pox 04m oH x ux com oH x_e\H oH x e mcoumx an o H1 o H1 m on mcmusmm cw monoumx Goons Haxad How mumo mumm xH means DISCUSSION Mechanistic Scheme for Azido Alkyl Phenyl Ketones: The products involved in the photochemistry of the azidoalkyl phenyl ketones indicate that the azido group does receive some of the triplet energy from the carbonyl group even at 366 nm where the absorbance of the azido group is approximately zero. An appropriate kinetic scheme is presented below: 0*1 ‘3 o " Q C (CH ) -N L (CH ) -N .' J 2 n 3 2 n 3 t .t O 1 O3 .C\_/—(CH ) -N 1£>.Cu(CH2)n-N3 2 n 3 t 033 k of: \\\——j—XCH2)n-N3 _§___9 (CH2)n—N3 * 0‘“ 1 C [(CH2)n-N3+QO ———> Q-CJ(CH2)n-N3 + 0‘3 kd' Q0 0*3 0 I! k 'I *3 Q C\—/—(CH2)n-N3 gt 0 C\—/—-(CH2)n-N3 O i'c' *3 03 ° \f(CH2)n-N3 —-—> \__/_(CH2)n'N° H 0 " - Ph Ph Q Lf—(CHz’n'N' —"'“’ \ + (\ /7 93:3 0 Q—E (CH ) -N +00 > II (CH ) -N + *3 U- 2 n 3 p \__/‘ 2 n 3 Op 94 0* OH " kr | . H -N o U—w—e .U—‘C . Type II Straight forward Stern-Volmer kinetic analyses of this scheme lead to equation 24. (Results). Mechanism for Formation of Photoproducts from y-Azido— butyrophenone: ' The 2-phenylpyrrole can be formed by two different path- ways. Since its rate of formation at 366 nm is quenched at the same rate as acetophenone, its formation depends on the rate of formation of triplet carbonyl. Interception of the triplet carbonyl by a quencher molecule would in effect quench both inter- and intramolecular energy transfer to the azide group. 2-Pheny1pyrrole must originate from the triplet azide. A likely method for the formation of 2-phenylpyrrole is by nitrene insertion into the carbonyl group to give the 138,177,178 ' © 9 *5 (f .{Lst ‘—" +N2 179 oxazirane. Emmons has proposed that such a substance could lead to the imino alcohol by a radical chain-like mechanism. 95 %% Emmons found that a similar imino alcohol lost water to form the conjugated eneimine upon attempted isolation. In the present system the nitrene could be the radical source. In the process of abstracting the hydrogen from the oxazirane an amine radical would be formed which could abstract a second hydrogen and form the aminoketone which would close to PPRL. In the present system an extended radical chain mechanism is not likely, but with all the possible radicals around it is not surprising that polymeric material is formed. Intramolecular addition of the nitrene to the carbonyl is certainly possible but it should also be expected to occur intermolecularly as well. When butyrophenone was quenched with butyl azide, no such addition products were observed (although they were not specifically looked for) nor does the work of Lewis and Saunderslim'176 suggest such products. Alternatively the 2-phenylpyrrole could arise from the hypothetical 6-iminoketone as shown below: (95—9 +5 eM—e 96 This mechanism is similar to that for the cyclization of aminoketone to PPRL. An exact analogy to this mechanism 196 for the cycliza- has been proposed by Mazzocchi and Thomas tion of y-iminoaldehydes to 2-substituted pyrroles. The y-iminoaldehydes are proportedly formed during the photolysis of substituted pyrrolidones. Any iminoketone which did not form 2-phenylpyrrole would most likely polymerize,166 or the 2-phenylpyrrole itself could polymerize. The behavior of AZBP in benzene is indicated in Scheme V. Calculation of GI and Stabilization Factor for the Azide Group: In hydrogen abstraction reactions the electrophilic triplet benzoyl group is quite selective in regard to both 7 C-H bond strength and inductive effects of nearby substitu- ents. Thus the Type II reaction would be expected to be a good monitor for the determination of the a value of the I azido group. A Hammett plot of relative rates of triplet state y-hydrogen abstraction has been reported by Wagner and Kemppainen.60 This plot has been reproduced (Figure XXXI) by plotting several of the log kr/k: values versus the CI values reported in the above reference. The p value for the 6-substituents was found to be -l.85 and p for the e-substitu- 7 -1 ents was -O.76. Since k: is known to be 12.5 x 10 sec for valerOphenone, the a value for the azido group can be calcu- I lated by equations 25 and 26 with the aid of kr values determined in this work for the azidoketones. 97 Ph/C\_fN5 80% 4 R/CL/‘Ns 00 O 5°/o Cydo k1) + anol Scheme V The Behavior of y-Azidobutyrophenone in Benzene Log Relative Rate Figure XXX: 98 0 0.2 0.4 Hammett Plot of Log of Relative Rates Versus o I 99 k r log k0 = -1.85 CI (25) r k r leg = -O.76 o (26) O I k r The GI value calculated fromtflmameasured kr value of AZVP was found to be 0.47, while the a value calculated from the kr I value of AZHP is 0.46. The log of the relative rates for the 5- and E-ketones are plotted (half-filled circles) in Figure XXX. These points are in good agreement with the data deter- mined by Wagner and Kemppainen. A value for a of 0.44 for I the azido group has been calculated from op and om.180 The measured OI value is in good agreement with this calculated value. The measured OI value indicates that the azido group is as electron withdrawing as the chloro group. The good fit of both the 6- and e-azidoketones with the same OI value, coupled with the previously found correlation for a large number of other substituents, suggest that the measured value is reasonably reliable. All substituents should stabilize a radical at the y-position,60 and this stabilization should be reflected in the transition state for hydrogen abstraction. Since pI for 60 y-substituted ketones has been estimated to be -4.3, a do value of -2.00 (using a for the azido group as 0.465) and I thus a relative reactivity of 0.0099 for AZBP relative was found to be 0.040. Thus the azido group has an apparent 100 radical stabilization factor of 4.0 which can be attributed to conjugation of its H-electrons with the incipient p-orbital. This group stabilizes the developing radical about as well as 60 a phenyl, vinyl, or cyano substituent. This is quite value) 60 interesting since the chloro group (with a similar OI stabilizes a radical with a stabilization factor of 8-23. This ability of the chloro group to stabilize a radical as well or better than groups containing Hsystems has been attributed to the lone pair electrons on chlorine. Since the azide group possess both lone pair electrons and a H system it might be expected to stabilize a radical center quite well. The measured stabilization factor suggests that the spx lone pair electrons are not available to stabilize the incipient radical. Two adjacent positive nitrogens would result if the lone pair electrons were delocalized onto the carbon. In the case where the radical is delocalized into the H systems of the azide a separation of a + and - charge results, which separation is probably not a favorable process. - -+ + - \. + - \ .+ — ,C-N=N=N€——-—>,C-N=N=N<———9/C=N-N=N - + o o - + - o + :C-N=N=Né——>:C-N-NEN:<-——>:-N-NEN Intramolecular Energy Transfer: The only study reported of variation in rates of energy transfer with increasing methylene chain length between chromo- 27 phores has been that reported by Cowan. In the systems he 101 studied, exothermic energy transfer from a carbonyl moiety 115 estimate to a styryl group occurs. If one accepts Lewis' of the triplet azide energy (75+80 kcal) to be close to the correct value, energy transfer to the azide group from the carbonyl is somewhat endothermic, in accord with the observed lower-than-diffusion-controlled intermolecular quenching rate constant. Cowan has indicated that the rates for energy transfer in the y- and 6-styryl ketones bracket the intermolecular rate constant of S x 109. He also observed that the rate of energy transfer from the B-styryl compound is seven times faster than that of the y-ketone, which is only 3.3 times faster than that of the d-ketone. These rates along with those measured for the azidoketones are listed in the Table X. Table X Rates for Intramolecular Energy Transfer in Phenyl Ketones ¢ CO(CH2)nX X n k et -CH=CH-Ph 2 7.2 x 1010 3 1.0 x 1010 4 3.3 x 109 -N3 3 2.6 x 108 4 2.3 x 107 5 <2 x 106 The rate of energy transfer from the carbonyl group to the azide group drOps off much faster than in the styryl 102 ketone case. The rate of energy transfer to the azide group in the y-ketone is about the same factor faster than the intermolecular rate constant as that observed by Cowan. However, the rate of decrease is about an order of magnitude for each of the azido ketones, while the styryl ketones show nowhere near that quick a drop in rate with increasing chain length. The exact mechanism of energy transfer is not yet known, but the currently accepted theory is that the n-orbitals of the carbonyl group must overlap with the H-orbitals of the acceptor group. Just how stringent these requirements are is not known. In any study of intramolecular energy transfer versus chain length there are at least two factors which must be considered: (a) ring size of the transition state, and (b) rotations about the methylene chain. 'Molecular models indicate that on the average the distance between the two chrom0phores remains nearly constant, however, the number of conformations in which the two ends of the molecule are nearly in contact decreases rapidly-with chain length. For energy transfer to occur from the carbonyl group to the azide the two groups must be parallel, whereas in the styryl group energy transfer could be to the olefinic H-system (parallel conformation) or to the phenyl ring (somewhat perpendicular conformation). Thus in the azido group there may well be even a greater dependence on the number of conformations in which energy transfer can occur compared to the styryl system. This might explain the much faster decrease in rates of intramolecular energy transfer observed for the azido ketones. 103 As the number of methylenes is increased from 3 to 5, the ring size for the transition state involving energy transfer increases from 5 to 7 (conceivably 8 to 10) in the case of the azido ketones. Clearly some ring strain is involved in the formation of the transition state. The ring strain would presumably be larger in the case of the azido group than in the styryl case because of the azide's allene type structure. Energy transfer to the azide may also involve some geometric change which would affect the ring strain in the transition state for energy transfer. It should be mentioned that in this Discussion two subtle factors have been ignored. It is not known whether the azido group undergoes any gross geometric changes in the energy transfer process. Also it is assumed that energy transfer from the azide to the ketone does not occur. Energy transfer from the azide to the carbonyl can explain why the acetophenone Type II quantum yield increases at 313 nm. If such transfer were reversible this would explain the lower than diffusion controlled rate constant observed for azide quenching. Such reversible energy transfer would increase the observed Type II ktT values. Charge-Transfer Quenching by the Azido Group: The intersystem crossing yield for AZBP is only 80% efficient. The 20% inefficiency may be due to singlet quenching of the carbonyl moiety by the azido group. This process would be endothermic in nature. Since the triplet quenching rate of the azide is only about 108 sec.1 it is unlikely that singlet 104 quenching by the azide group would compete with the rapid 11 sec-1) intersystem crossing rate of phenyl ketones (about 10 to the tune of 20%. Alternatively the azide could form a charge transfer complex with the excited carbonyl which would subsequently decay to the ground state ketone or possibly produce some uncharacterized product. Indications for Further Research: This work has been both intriguing and challenging to the author. As always new research requires a certain amount of "mopping up" and elicits a certain amount of further research: (1) It would be interesting to further extend the meager solvent studies undertaken for these ketones. (2) It would be interesting to study the benzene substituted compounds, i.e. p-azidovalerophenone etc. ESR studies of these compounds could be easily performed. In this work the ESR spectrum of p-azido— acetophenone was observed at 77°C. Whereas the only ESR spectra for the alkyl azides have been observed at 49K. (3) It would be interesting to study other pseudohalides, i.e. -SCN and -NCO both in the y- and 6-positions and on the benzene ring. A study of 6-thiocyanato- valerophenone was initiated here, but its low quantum yield and the fact that butylthiocyanate has the same retention time as acetophenone caused this work to be put aside. (4) 105 It would be appropriate to find a molecule that would quench triplet azides to study the rate constants of ring closure and azo-formation in appropriate compounds such as 2-azidobiphenyl whose rates have been measured only by flash studies. N-SUBSTITUTED-4-METHYL-4-BENZOYLPIPERIDINES RESULTS Part III Synthesis: Three separate syntheses of these compounds were considered (Scheme VI). Pathway III was ruled out since several steps would be required to obtain the starting chloroketone (6 steps overall). Since a small amount of the N-alkylated ketone neceSsary for the synthesis via pathway I was available, several attempts to prepare the desired compound using Rathke's base (lithium diisopropyl amine)181 were undertaken. The ketonic material obtained appeared,by NMR analysis,to be about fifty percent alkylated. Since purification of the two similar ketones was seen as a problem, it was decided to use synthetic pathway II. (1158 was achieved, Synthesis of the reported cyano compoun albeit in low yield (38% overall). The next two steps were accomplished in an unexpected 60% overall yield. Several bases were used in the alkylation procedure with phenyl sodium giving the best overall yield. Rathke's base (lithium cyclohexylisopropyl amine) and trityllithium are sufficiently useful in the case of the N-benzyl compound, but in the case of the N-methyl compound the alkylated nitrile co-distills with the solvents used in the reaction. 106 107 Pathway I 9- M 9‘ (SQ ESCh/VGIEF‘ 1 88 e s 4% N we: O H R R Pathway II W 8% __> (SW S’QQE I (5:? 1.Base R IZ Pathway III Q ' O Q.OH HO Scheme VI Possible Synthetic Routes for the Preparation of N-Methyl-4-Methyl-4-Benzoylpiperidine 108 l-methylcyclohexyl phenyl ketone was prepared from cyclohexane carboxamide by method II. Identification of Photoproducts: Irradiated solutions of these compounds yield relatively simple VPC traces. Benzaldehyde was identified as a product of all the ketones by comparison of its VPC retention time to that of the pure material. 4-methyl-N-methylpiperidine was assumed to be formed but would be lost in the benzene trace. Its olefinic counterpart formed in the Type I reaction is also assumed to be lost in the solvent peak. An isomer of N—methyl-4-methyl-4-benzoylpiperidine(NMMBP) was isolated and identified as the Type II cyclobutanol. Three grams of NMMBP were irradiated in the presence of 0.1 M naphthalene through a vycor filter, and the resulting yellow oil was chromatographed on an alumina column. Two grams of 90-95% pure (NMR analysis) material were obtained. This compound had spectra consistent with the cyclobutanol:182 ”9% 3% X=CH2 X=NCH X=NCH2Ph VPC analysis of irradiated l-methylcyclohexylphenyl ketone (MCPK) solutions also showed only two high-boiling products, benzaldehyde and a peak presumed to be the cyclobutanol reported by Lewis.66 N-benzyl-4- methyl-4-benzoylpiperidine (BMBP) showed benzaldehyde and a peak presumed to be the 109 N-benzylpiperidine. The Type II reaction was not studied for BMBP. When photolyzed samples of NMMBP were injected on Col-4 at high temperatures and flow rates (1700 at double the flow rate used to analyze the Type II product), materials which appear to be oligomers were observed. Quantum Yields: Quantum yields were determined by irradiating solutions of the ketone of interest concurrently with valerophenone actinometer. Since it was assumed that the amine portion of one NMMBP might quench the triplet of another and that energy transfer might occur between conformers, all work with these ketones was carried out at 0.04 M ketone concentration (the lowest concentration with an Optical density greater than 2.00). In order to compare the behavior of these ketones to that of MCPK, it was necessary to measure its quantum yield at 0.04 M ketone concentration. (a) Type I Cleavage: Type I quantum yields of the amino ketones were determined with and without the presence of varying concentrations of dodecanethiol. Benzaldehyde formation was monitored with decyl alcohol as standard. Since little is known of the behavior of the Type I reaction in various solvents, the quantum yield was determined in pyridine and in 1- propanol. In general, the quantum yield is lowered in these polar solvents. The Type I quantum yield of a 0.04 M solution of MCPK was measured in the presence of 0.0l M 110 dodecanethiol. The Type I quantum yield of MCPK at this concentration of ketone is significantly higher than that reported by Lewi366. These results are listed in Table XI. (b) Type II Elimination: Type II quantum yields for photocyclization of NMMBP were measured in benzene,pyridine,various concentrations of l-propanol, and a 0.04 M dodecanethiol solution. The Type II quantum yield was depressed in the presence of pyridine and about equal to that in benzene in l-prOpanol. An attempted measurement of the Type II quantum yield in 50:50 methanol:benzene gave a Type II quantum yield too small to measure. The Type II quantum yields for phtocyclization of a 0.04 M solution of MCPK were measured in neat l-propanol, pyridine, and neat acetonitrile/l% water. The highest quantum yield obtained was that in l-propanol. The observed Type II quantum yield of MCPK was only slightly lower than that observed by Lewis.66 As in the case of NMMBP, pyridine depresses the Type II quantum yield from MCPK. These results are listed in Table XII. (c) Disappearance: The disappearance quantum yield of NMMBP was measured in benzene, pyridine, varying concentrations of l-propanol, and 0.04 M dodecanethiol. In benzene and pyridine the disappearance quantum yield was five times that of the sum of the quantum yields for formation. In l-propanol the disappearance quantum yield was only four times that of the sum of the quantum yields for formation. In the presence of 111 Table XI Type I Quantum Yields for 0.04 M Ketones at 313 nm Solvent OBSERVED QUANTUM YIELD NMMBP BMBP MCPK benzene 0.016i0.005 -—— --— 0.01 MSH/benzene 0.061 0.092 0.30 0.02 MSH/benzene 0.13 0.16 --- 0.04 MSH/benzene 0.16 --- --- 0.5M pyridine 0.00 --- --- 10% PrOH/benzene 0.0056 --- --- 20% PrOH/benzene 0.0030 --- --- 30% PrOH/benzene 0.0024 --- —-- 40% PrOH/benzene 0.0022 --- —-— 1.0 M naphthalene the disappearance quantum yield also equals the sum of the quantum yields of formation of products. These data are listed in Table XII. Behavior in the Presence of Quenchers: (a) Type I: Stern-Volmer slopes for quenching of the Type I reaction of 0.04 M benzene solutions of NMMBP and BMBP were obtained at 313 nm in the presence and absence of 0.02 M dodecane- thiol using l-methylnaphthalene or naphthalene as quencher. In the presence of mercaptan both BMBP and NMMBP give plots with identical slopes in the presence of low concentrations 112 Table XII Type II Quantum Yields for 0.04 M Ketones at 313 nm Solvent OBSERVED TYPE II¢ DISAPPEARANCE¢ NMMBP MCPK NMMBP benzene 0.017 —-- 0.139 benzene/ naphthalene 0.06 -—- 0.06 0.5 M pyridine 0.0098 0.032 0.048 PrOH --- 0.18 --— 0.04M SH/benzene 0.053 --- 0.22 acetonitrile --- 0.12 -—- acetonitrile/ 1% H20 --- 0.12 --- 50% MeOH/benzene 0.00 --- --- 10% PrOH/benzene 0.017 --- 0.090 20% PrOH/benzene 0.014 --- 0.068 30% PrOH/benzene 0.016 --- 0.067 40% PrOH/benzene 0.015 --- 0.069 113 Table XIII Quenching Data for 0.04 M Ketones Ketone Solvent ktrIa ktTIIa NMMBP benzene 250b <0.2 (0-2)c 0.02M SH/benzene 267 --- BNBP 0.02M SH/benzene 275 --- MCPK benzene 3.3d --- acetonitrile/1%H20 --- 0.25d anaphthalene quencher unless noted cinitial slope from sensitization slope dN-methylpiperidine quencher of quencher. At higher concentrations of quencher the plot curves slightly upward for NMMBP. This same phenomenon is observed when the Type I reaction from the cyclohexyl ketone is quenched by N-methylpiperidine in the presence of mercaptan. In the absence of mercaptan the Type I Stern-Volmer plot for NMMBP curves downward. The observed ktT values observed for NMMBP and BMBP are similar to those values of other phenyl ketones possessing a-substituents. The obtained data are listed in Table XIII and the plots are reproduced in figures XXXI and XXXIII. 114 (b) Type II: In the presence of 0.02 to l M naphthalene at 313 nm or 366 nm the Type II quantum yield in benzene of NMMBP increases. This behavior is also observed in the presence of tetramethylbutadiene at 366 nm. The maximum increase in quantum yield is reached in the presence of about 1 M quencher concentration, and is approximately four times that observed in benzene. Even in the presence of high concentrations of naphthalene (l-8M) the Type II quantum yield does not decrease. When tetramethylbutadiene was used as quencher at 366 nm the quantum yield did start to decrease at about 2 M quencher concentration. The highest slope indicated by this plot (obtained by subtracting 0.5 M quencher from each point and using the 0.5 M quencher tube as the 0 point reference tube) is 0.2. This value is at best an estimate, but does indicate that the Type II reaction comes from a fast triplet rather than from the singlet. The plot is reproduced in Figure XXXIV. Since alcoholic solvents should hydrogen bond with the nitrogen lone pair electrons on NMMBP,89 the ability of the lone pair electrons to stabilize the incipient radical should be reduced and the rate of hydrogen abstraction slowed down. Also it is postulated that alcoholic solvents slow down the rate of intramolecular charge transfer interactions.89 However, the alcoholic solvents inhibit revertible hydrogen transfer of the biradical thus increasing Type II quantum yields.4 Since a kt: value for the Type II reaction was not 3.0' O BMBP O NMMBP in presence of no thiol .NMMBP in presence of thiol l j l 4 6 8 16 x10’3 [Naphthalene] Figure XXXI: Stern-Volmer slopes for Type I reaction of N-methyl-and N-benzyl-4-methyl-4-benzoylpiperidine 1.5 r 0k} 0 1.0 j 1 1 l 2 3 ' DI-methylpiperidine] Figure XXXII: Stern-Volmer lepe for Type II reaction from l-methylcyclohexylphenyl ketone by N-methyl- piperidine 116 ale 0 I I 1 l L J 1 J 1 2 3 4 s 6 7 8 x10- Ev-methylpiperidiné] Figure XXXIII: Stern-Volmer plot for benzaldehyde formation of N-methyl-4—methyl-4-benzoylpiperidine i 4 6 5 Eetramethylbutadiené] Figure XXXIV: Stern-Volmer plot for Type II formation of N-methyl-4-methyl-4-benzoylpiperidine at 366 nm 117 obtainable in benzene solutions, attempts were made to quench the Type II reaction in alcoholic solvents. When the diene quencher (t—piperylene) was added to neat l- propanol, Efbutanol, or l-pentanol the solutions turned cloudy, thus 50:50 l-propanol : benzene was chosen as the solvent system. Irradiation of 0.04 M ketone solutions containing 0-4M Efpiperylene were irradiated at 313 nm. As in benzene, the quantum yield of the Type II product increases in the presence of quencher. The‘solution containing 0.5 M piperylene was thus used as the reference solution as described above. The solutions containing 1 and 2 M piperylene visibly quenched the Type II product with a slope of about 0.4 M-l. However the tubes containing 3 and 4 M piperylene showed only little quenching (slope = 0.02 M'l). Since it is possible that the amine moiety of NMMBP can photoreduce the ketone portion of another NMMBP, the Type II reaction from MCPK was quenched by N-methylpiperidine The quenching slope was found to be about 100 times lower than that observed by Lewis66 for diene quenching. The data are shown in Table XII and the plot reproduced in Figure XXXII. Sensitization Studies: Photolysis of 0.04 M NMMBP in the presence of low concentrations of gigfpiperylene (0.05 M or below) at 313 nm yields a VPC trace indicating three peaks in the area of Eggggfpiperylene. At higher piperylene concentrations ( 0.1M or above) the normal VPC trace for cis-and trans-piperylene is observed. A sensitization plot for NMMBP was obtained 118 3 <0 or .555 4 2 1 J l 1 l l 2 3 4 E/cis-piperylena Figure XXXV: Sensitization Plot of N-methyl-4-methyl- 4-benzoylpiperidine 119 by irradiating 0.04 M solutions of the ketone in the presence of varying amounts of piperylene at 313 nm. This plot curved downward. Two different studies indicated that the intercept of the lower part of the curve is approximately unity. The average of two different studies indicate that the upper portion of the curve has an intercept of 3.05. The slope obtained from the lower portion of the curve is 0.2 M-l. This curve is reproduced in Figure XXXV. Disappearance of the Type II Photoproduct: The increase in the Type II quantum yield in the presence of low concentrations of quenchers and the inability to quench the Type II product were preplexing problems. It was possible that the Type I products were scavenging the starting ketone and the Type II product. In the presence of quenchers the Type I reaction would be quenched and less NMMBP and Type II product would disappear. To test this hypothesis, a 0.04 M benzene solution of NMMBP containing 0.004 M Type II product was irradiated at 313 nm. When the irradiated sample was compared to the unirradiated sample, 15% of the Type II product had disappeared from the irradiated sample. Since an increase of about 33% in the Type II product should have been observed, about 50% of the product disappeared during the irradiation. 120 NMR Studies on Ground State NMMBP: (a) Low temperature proton NMR: The room temperature NMR spectrum of NMMBP in freon 11 with TMS standard obtained from the Varian HA-100 spectro- meter was identical to that obtained on the Varian T-60 spectrometer. Broadening of the N-CH -CH3, and -CH 3’ 2 signals was observed but no splitting into two distinct signals was observed even at -900 C. (b) 13C Low Temperature NMR: The room temperature proton decoupled 13C spectrum of NMMBP in freon 21 with TMS standard is reproduced in figure XLV. The peaks were compared and assigned in accord with the 197 197 shifts observed in piperidine , N—methylpiperidine , and MCPK188. The assignments were also assisted by the proton coupled room temperature spectrum [:; 4-methyl-25.4 (quartet); C3-35.9 (triplet); N-CH -46.2 (quartet); C -46.5 (singlet); 3 l 02-53.0 (triplet); C=O-208.5; aromatics 128.1, 128.4, 131.1, 139.§] . The J value for the couplings in the proton coupled spectra were 5.61 ppm. The carbonyl signal remained a singlet down to -96°C. Apparently both the equatorial and axial carbonyl carbons have identical chemical shifts. At about -150 the a-methyl signal is broadened and below this temperature shows two peaks separated by 8.3 ppm (19.8, 28.1). At -50°C the ring carbons show two peaks separated by 2.2 ppm (C3-34.0, 36.2). The difference between the shift of the methyl group at room temperature and each methyl signal at -700 indicates a 30%:70% axial: equatorial ratio, while the 121 difference between the shift of the ring carbons at room temperature and both signals at -70°C indicates a ratio of 20%:80% axial:equatorial. Thus an average population of 25% axial conformer to 75% equatorial conformer is predicted for NMMBP. This data together with the photochemical data indicate that a large portion (=40%) of the equatorial conformer of NMMBP is missing. DISCUSSION Ground State Conformations of NMMBP: Figure XXXVI shows the possible ground state chair conformations and one high energy boat conformation of NMMBP. :2. a,a H H “I ere m9 II b" Figure XXXVI Ground State Conformations of NMMBP At present there is a controversy in the literature as to whether the methyl group or nitrogen lone pair is in the axial or equatorial position.184.6 Booth and Little184 indicate that N-methylpiperidine Prefersa conformation in 122 123 which the electron pair on nitrogen is axial, while 185 Blackburne indicates the preferred geometry is that with the electron pair equatorial. Lambert,186 as well as Booth and Little and Blackburne, indicates that the preference of the nitrogen lone pair depends on substitution on the piperidine ring. In any event it is interesting to note that the equatorial position is particularly suitable for delocalization of the lone pair into various bonding situations of the 187 whereas such interactions are not saturated ring, possible for the axial lone pair electrons which are pointed away from the molecule. According to Lewis66 for the analogue MCPK, the ratio of conformers with the benzoyl moiety axial to that equatorial is l.0:2.7 at 25° or about 25% of the molecules exist in the conformation with the benzoyl group axial. The 13C NMR spectra for NMMBP indicates that NMMBP exists in about the same ratio of conformers. Only in conformation "b" are the nitrogen lone pair electrons as close to the carbonyl as they can get in y-di- methylaminobutyrophenone. Molecular models indicate that in conformation "a,e" the distance between the carbonyl group and the lone pair electrons is approximately six 2. However, the p orbitals of the two groups cannot attain a parallel orientation. Conformer "e,e" has the Carbonyl group and the nitrogen lone pair electrons in the preper geometric alignment postulated for "synchronous fragmentation" 187 reactions, and thus may be set up for through bond charge- 124 transfer interactions. In conformer "a,a" the nitrogen lone pair electrons are parallel with the hydrogen to be abstracted in the Type II reaction and such stabilization of the incipient radical should provide an extremely fast rate for hydrogen abstraction as well as revertible hydrogen transfer. Interaction of the carbonyl moiety with the back lobe of the sp3 orbital in conformer "a,a" might also be possible. This type of interaction might also be able to occur in conformer "a,e". Conformationally Interesting Compounds: 62-66 Lewis has measured the rates of hydrogen abstraction for several conformationally interesting ketones. For convenience the data are reproduced in Table XIV along with the information obtained in this work. In the Table,¢ d IIan 41 are the quantum yields for the Type II and Type I reactions respectively. ¢el and 4c are the quantum yields for elimination and cyclization reactions. PrOH and EfBuOH are l-propanol and Egrtfbutyl alcohol respectively. SH is mercaptan and 32 is benzene. Intermolecular Energy Transfer Between Conformers: Until quite recentlyles'189 energy transfer between identical molecules has either been ignored or found to be negligible in those systems where such transfer was reversible.168 In the present systems (NMMBP and MCPK) energy transfer can be expected to be irreversible because of the low concentrations of ketone used and because of the relatively short lifetimes of the Type II conformers. Turro 125 Table XIV Rate Data for Conformationally Interesting Ketones 0T1 \M Ket°ne S°lvent @el 4c 1/.x108 4 l/uxlU" Valerophenone Bz 0.33 0.07 1.2 --- --- t-BuOH 1.00 --- --- --— --— 2-n-propyltetralone B2 0.09 0.03 5.9 --- --- PrOH 0.36 0.03 --- --- --- - 1)- Bz —-- 0.14 9.2 --- --- 34463832383: PrOH ___ 0.34 ___ -__ ___ endo-2-benzoyl- '——5 Bz 0.10 —-- 70 --- --- nor ornane t-BuOH 0.13 ___ ___ ___ ___ exo-Z-benzoyl- ___ ___ --- HSEbornane B2 0.13 0.12 endo-Z-benzoyl- Bz --- 0.49 0.86 --- --- 2-methylnorbornane EfBuOH --- 0.63 --- --- --- exo-Z-benzoyl- Bz --- --- --- 0.032 0.12 2-methylnorbornane Bz/SH --- --- --- 0.096 --- 2-benzoylbicyclo- Bz 0.041 --- 100 --- --- 2.2.2] octane E-BuOH 0.053 ...... -..... --.. --.. 2-benzoyl-2-methyl- Bz --- 0,13 3,0 --- --- bicyclo [2.2.2] E-BuOH --- o. 26 --- --- --- octane cyclohexylphenyl Bz --- 0.008 17 --— --- ketone PrOH --- 0.13 --- --- --- 4-(Efbutylcyclo- Bz 0.024 --- 68 --- --- hexylphenyl ketone PrOH 0.098 --- -:- --- --- MCPK BZ --- 0.045 1.7 --- —-- PrOH --- 0.21 --- -—- --- Bz/SH --- --- --- 0.20 0.25 Cyclopentylphenyl B2 0.22 ___ 0.025 ___ ___ ketone l-methylcyclopentyl- Bz --- 0.19 0.13 --- --- phenyl ketone Bz/SH --- --- --- 0.03 0.13 y-Dimethylamino- Bz 0.056 --- 80 --- --- butyrophenone MeOH 0.25 --- l7 --- --- NMMBP Bz --- 0.06 --- 0.016 0.19 Bz/SH --- 0.053 --- 0.16 0.19 126 189 and Lechtken have indicated that the rate of energy 6 1 transfer between acetone and acetone-d6 is about 3 x 10 M- -1 188 sec . Lewis has measured the rate of energy transfer from the equatorial to the axial conformer in cyclohexyl- 8 M-1 sec-l. In this study an phenyl ketone (CHPK) as 4 x 10 attempt was not made to determine the rate of energy transfer between the conformers nor has Lewis performed a study on MCPK. The 50% lower Type I quantum yield of NMMBP relative to MCPK yet the identical slopes of the two compounds is an intriguing problem. Either there is less Type I conformer in NMMBP relative to MCPK or the lowered quantum yield can be due to two factors: intermolecular quenching by the amine moiety of NMMBP (see next section) or intermolecular energy transfer from the equatorial conformer to the axial conformer. Assuming one half the difference is due to each process, 25% of the difference between the Type I quantum yield of NMMBP and MCPK is due to the energy transfer process. From the lifetime (1/1 = l/kde+ 1/ketENMMBi3) ) of the Type I conformer the rate of energy transfer from the equatorial conformer to the axial conformer at 0.04 M NMMBP can be estimated at about 4 x 106 sec-1. Since the methyl group provides some steric hindrance to energy transfer, the rate of energy transfer for NMMBP might be expected to be somewhat slower than that observed for CHPK. In actuality the rate of energy transfer is only slightly less (about a factor of two) slower than that reported by Lewis for CHPK. 127 Steric Effect to Intermolecular Charge-Transfer Quenching: Since intermolecular charge-transfer quenching and subsequent photoreduction of the triplet ketone by the amine moiety of NMMBP is conceivable, the Type I and Type II reactions from MCPK were quenched using N-methylpiperidine as quencher. The quenching plot of the Type II process in acetonitrile/1% H 0 was linear and indicated a quenching 2 rate about 100 times less than that observed for dienes. The quenching plot of the Type I process curved upward but the highest slope indicated a quenching rate by the amine at least 20 times slower than diene. The lower portion of the curve indicated a rate 100 times slower than diene and this is probably the more reasonable number. The diene quenching value was obtained by Lewis65 for some unspecified ketone concentration and the amine quenching data was observed at 0.04 M ketone concentration. Since kt'r is expected to decrease with ketone concentration, the 100 times difference in the quenching rate observed for amine relative to diene is probably on the order of only 50. Since the Type I conformer can sensitize the Type II conformer, the quantum yield and thus the k T values will change with ketone t concentration. The Type I process for MCPK at 0.04 M ketone concentration was measured as 0.3 versus 0.21 reported by Lewis. The Type II quantum yield was only slightly lower than that reported by Lewis (0.18 versus 0.21 respectively). Still the difference between amine and diene quenching is at least a factor of fifty, so that k for the quenching of NMMBP 8 M-1 Sec-1. The rate t by N-methylpiperidine is about 1 x 10 128 for intermolecular quenching by the amine moiety of 0.04 M NMMBP would be about 4 x 106 sec-1. Thus both amine quenching and intermolecular energy transfer should compete about equally with the Type I process from NMMBP if they occur at all. Sensitization Studies: Attempts were made to determine the intersystem crossing yield of NMMBP by sensitizing the isomerization of piperylene. Two such plots were obtained in which the intercept for the lower part of the curve tended to one. Two different studies were also performed to determine the intercept of the upper portion of the curve. Values of 2.9 and 3.18 were obtained indicating an intercept of 3.05. The plot is interesting in that it curves downward. Such behavior is expected for a system in which two reacting triplets can sensitize piperylene.170 Obtaining an intercept for the lower portion of the curve is not entirely accurate. However, it can be seen that the intercept of the lower portion of the curve is headed towards one and not two (4isoy-dimethylaminobutyrophenone (DMABP) = 0.58). Clearly there is less charge-transfer quenching of the carbonyl by the amine in NMMBP than in DMABP. And it appears that there are no charge-transfer interactions of the type that exist in DMABP in NMMBP at all. The upper intercept indicates the population of each ketone 190 present . The intercept of 3.05 for the upper portion of the sensitization curve indicates about 1 Type I conformer 129 for every 2 Type II conformers. This is not the ratio Lewis6S obtained for MCPK from 13 C NMR studies, and the NMR studies in this report indicate that the pepulation of the Type I conformer to the Type II conformer for NMMBP is about 3 to 1. Deactivation of conformer "e,e" by through bond charge- transfer interactions seems to be the best explanation for the observed discrepancy. It is interesting that the ktr (0.2) of the lower portion of the curve is the same as that estimated for the Type II reaction (0.2). This observation does not rule out the possibility that there is some species other than conformers "e,a" or "a,a" and "a,e" sensitizing piperylene. Disappearance of Type II Product: Since the Type I product reacts with the Type II product and presumably with the parent ketone, the 4 values obtained in benzene for NMMBP cannot be taken as reliable. An indication of the true 4 values however is obtained from the studies in the presence of dodecanethiol and quenchers. Since the quantum yield for disappearance equals the quantum yield for formation of products in the presence of 0.04 M mercaptan, the mercaptan traps all the radicals thus preventing them from reacting with the Type II product. Thus the 4I in the presence of 0.04 M mercaptan is probably close to the correct value. Since 0.04 M mercaptan can intercept some of the Type II biradicals, the Type II quantum yield in the presence of high concentrations of quenchers (where the Type I reaction is almost completely quenched) is probably closer to the correct value. 130 Type I and Type II Quenching Slopes: It is interesting that the Type I quenching plot of NMMBP curves downward at about 50% quencher concentration, since Lewis65 indicates that the Type I quenching plot of MCPK is linear out to >90% quenching. This downward curvature indicates that some of the Type I product from NMMBP is either coming from the singlet or some other conformer. This other conformer is probably not the Type II conformer since neither MCPK nor Efbutyl-l-methylcyclo- hexylphenyl ketone (BMCPK) give Type I products from the Type II conformationés. That the Type I reaction is coming from some other conformer is reinforced by the observation that even at high concentrations of quenchers ( 0.5 to 1M) where the Type I reaction should be completely quenched assuming a lifetime of 2 x 107 see.1 the Type II quantum yield is still slightly increasing. The inability to obtain a good Type II quenching slope can possibly be due to three factors: the Type II reaction occurs from 1) the singlet state, 2) an extremely fast triplet, or 3) an anomaly due to the Type I reaction. The occurrence of the Type II reaction from the singlet is unlikely although possible in the light of the work of Ersfeld.191 It is entirely possible that the Type II reaction occurs from an extremely fast triplet, but in l-propanol the Type II reaction should be slowed down to about the rate Lewis observed for MCPK: Thus it is likely that the inability to quench the Type II reaction is due to the fact that all 131 the Type I product is not quenched even at high concentrations of quenchers. A small percentage of radicals reacting with the Type II product could cause just enough difference in the presence of differing amounts of quencher to observe no effective quenching. Partitioning of Energy in Excited NMMBP: The sensitization,quenching, and quantum yield studies coupled with the NMR studies on NMMBP indicate that at least three triplets are involved in the photochemistry of NMMBP. This third triplet appears to arise at the expense of the Type I conformer. The observed results might also be explained by the Type II conformer photoeliminating to yield the corresponding eneaminoketone, which could subsequently polymerize with the Type I conformer, or sensitize piperylene. This explanation 188 does not see such is not likely, however, since Lewis eliminations from MCPK or BMCPK. Neither was there any evidence in the VPC traces of irradiated NMMBP of such an eneaminoketone being formed. Alternatively conformer ”e,e" could by through bond charge-transfer interactions (similar to the mechanism postulated for the participation of the nitrogen lone pair electrons in synchronous fragmentation reactions)187 deactivate the Type I conformer. Such a species might be able to senistize high concentrations of piperylene and give Type I products at a different rate than observed for conformer "e,a". The behavior of NMMBP in benzene can be 132 represented as shown in Scheme VII. 4. II CH2 Behavior in Polar Solvents: The behavior of NMMBP in polar solvents not containing a radical trap probably does not indicate much, since the results probably only reflect the behavior of the formed Type I free radicals in differing solvents. The results observed in this work do suggest that scavenging by the Type I radicals is probably occurring in other systems where competitive Type I and Type II reactions can occur i.e. MCPK, a,a-dimethylvalerophenone. (a) Pyridine : Normally pyridine increases the Type II quantum yield, maximizing it at about 0.5 M pyridine concentration. It is thus interesting that pyridine decreases the Type II quantum yield of NMMBP and MCPK by about a factor of 2.0. In NMMBP the disappearance quantum yield and Type I quantum yield are also lowered by about a factor of 2.0. Lewis192 has suggested that the order of magnitude decrease in the rate kr for MCPK relative to CHPK is due to interaction between the grthgfhydrogens of the benzene ring and the a-methyl group which hinders rotation of the biradical. Certainly if the pyridine forms some complex ‘ *4 I 4 o 225% ___, ~91» % N 0 .043 0‘03 -CH 0 3 F/ (R ¢—C NMMBP ”45% #4» ————w 43% 1:. NMMBP CD (543 o \(OO\O 9? ¢—-C 9 ¢__.%o o O ¢~9_l 32°lo 32°/o .‘: (E) 212’ N o s . C2 1330/9 { FREE RADICALS Scheme VII Behavior of N-methyl-4-methyl-4-benzoylpiperidine in Benzene 134 with the triplet carbonyl, the sheer bulkiness of the formed complex would slow the necessary rotation to produce cyclobutanol even more and might account for the observed decrease in the quantum yields. The decrease in the Type I quantum yield in pyridine containing no mercaptan has no real precident in the literature. 193 has indicated that about a two-fold However, McGrath decrease in the Type I quantum yield for a,a- dimethyl- valerophenone was observed in Efbutanol and acetonitrile. (b) Alcoholic Solvents: Alcoholic solvents normally increase Type II quantum yields, and this behavior was noted for MCPK. The expected increase for the Type II process of NMMBP was not observed in either methanol or l-propanol. In fact 50% methanol drastically reduces the Type II quantum yield, while the quantum yield in varying concentrations of l-propanol shows a slight decrease, then rise to the original value. (It is interesting that this same behavior in 1-propanol is observed for MCPK when varying concentrations of amine are added to the solutions.) The alcoholic solvent should interact with the amine. The formed -;(CH3)3-H-5R moiety would have a much more positive OI value than that of the -N(CH3)3 group thus giving rise to a reduction in quantum yield (i.e lone pair electrons less available to stabilize the forming radical). Coupled with 89 the results of Wagner and Kemppainen on DMABP where methanol increases the quantum yield but decreases kr' 135 these results suggest that there is little or no intramolecular charge-transfer quenching of the triplet carbonyl by the amine. The slight lowering then rise of the Type II quantum yield with varying concentrations of l-propanol and the initial quenching then rise to the observed 4 in the quenching studies on NMMBP in l-propanol indicate that the interactions of the alcohol with the amine, the inhibition of revertability, and the disappearance of the Type II product are in competition with one another. Which process will rule seems undeterminable at present. Indications for Further Research: The study of NMMBP has raised a number of questions, some of which would be answered by the following extensions of this work. 1) Substitution of different groups for the methyl group in the 4-position,i.e a trifluormethyl group would be interesting. This larger group should change the relative populations of each conformation thus giving rise to different amounts of Type II and Type I products. Substitution of an ethyl group for the methyl group might give rise to the following compound: 0 ' CH3 2) Substitution of a pfmethoxy group on the benzene ring of the benzoyl group would be of interest since the Type II reaction should be slowed down. Hopefully this 3) 4) 5) 6) 136 compound would provide a handle for measuring the lifetime of the Type II conformer. To test the hypothesis that through bond charge transfer might be the mode of deactivation of NMMBP, the synthesis and photochemical studies of the following compounds might be considered: ‘0 @N t—vb C3 Also the study of compounds containing large groups(t-butyl) which would look the molecule into conformations "a,a" and "6:8" would be appropriate. Not totally relevent, but interesting, would be the study of: ((3.8ng The bond energy for the N-H bond is about 3-kcal less than that of the C-H bond and it would be interesting to see if this compound would Type II. The cyclization products from the Type II reaction would be B-lactams. A study of the quenching of sterically hindered ketones by amines should be undertaken. It would be interesting to further study the effects of polar solvents on the Type I reaction in the presence of a radical trap. In conjunction with this study it would be appropriate to study the effect of pyridine on the Type II reaction of other sterically hindered ketones. EXPERIMENTAL Part I Preparation and Purification of Materials Solvents: a. Benzene: Benzene (Mallinckrodt)of nanograde quality was purified by stirring over concentrated sulfuric acid several times for several days. After the sulfuric acid was removed, the benzene was washed with a 10% aqueous solution of sodium bicarbonate followed by several washings with water and subsequently was dried over anhydrous calcium chloride (4 mesh). The benzene was finally distilled from P205 through a 45 cm column packed with glass helices. A reflux ratio of 10:1 or larger was maintained at the distilling head and the middle 80% was collected. b. 2-Propanol: (Fisher Scientific) was distilled from sodium through a 20 cm glass helices packed column. The center cut was collected. c. Cyclohexane: (Fisher Scientific) was stirred over sulfuric acid until the acid no longer turned yellow. It was then washed as described for benzene. It was finally distilled from P205, the middle fraction being retained and stored under nitrogen. d. Pyridine (Mallinckrodt)was distilled from barium oxide and the middle fraction retained. 137 138 e. Methanol: (Fischer Scientific) was distilled from magnesium shavings. The middle cut of about 60% was retained. f. Methylcyclohexane: (Eastman, spectral grade) was passed over alumina and used as received. 9. Heptane (J.T. Baker, spectral grade) was used as received. h. Ethanol: was used as received. i. Dodecanethiol: (Aldrich) was distilled at reduced pressure. j. l-PrOpanol: (Fischer Scientific) was distilled from sodium as in "b" above. k. Acetonitrile: (Fischer Scientific) was distilled from potassium permanganate. Sulfuric acid was added to the distillate and the ammonium salts filtered. The material was redistilled and stored under argon. Internal Standards: The standards used in this thesis were purified as indicated below by Peter J. Wagner4 unless otherwise noted. a. Dodecane: (Aldrich Chemical Co.) was purified analogous to benzene with distillation under reduced pressure. b. Tetradecane: (Columbia Organic) was purified as dodecane. c. Hexadecane: (Aldrich Chemical Co.) was purified as dodecane. d. Heptadecane: (Aldrich Chemical Co.) was purified as dodecane. 139 e. Octadecane: (Aldrich Chemical Co.) was treated as benzene with the final distillation being replaced with a recrystallization from ethanol: f. Nonadecane: (Chemical Samples Co.) was purified as octadecane. g. Decyl alcohol: (Eastman) was distilled at atmospheric pressure by Dr. Joseph McGrath. Quenchers: a. Naphthalene: (Matheson Coleman and Bell) was recrystallized three times from ethanol. b. l-Methylnaphthalene: (Aldrich Chemical Co.) was used as received. c. gigfpiperylene: (Chemical Samples Co.) was used as received. It contained 0.3% of the trans isomer. d. Biphenyl: (Matheson Coleman and Bell) was recrystal- lized three times from ethanol. e. 2-Chlorobiphenyl: (K&K Laboratories) was recrystal- lized four times from ethanol. f. 3-Chlorobipheny1: (K&K Laboratories) was fractionally distilled under reduced pressure. The middle fraction boiling at 101-2o at 0.1 mm Hg was retained. The material was passed over alumina and frozen from ethanol several times. 9. 4-Chlorobiphenyl: (K&K Laboratories) was recrystal- lized three times from ethanol. h. 2—Methylbiphenyl: (K&K Laboratories) originally about 80% pure was purified by preparative vapor phase chromatography. Two passes through a 6' x a" aluminum column packed with 15% 140 Carbowax 20M on Chromosorb W were necessary to obtain material 99.5% pure (analyzed by VPC on Col-3). i. 3-Methylbiphenyl: (K&K Laboratories) was distilled, passed over alumina, and frozen from ethanol several times. j. 4-Methylbiphenyl: (K&K Laboratores) was recrystal- lized from ethanol several times. k. 2,2'-,3,3'-, and 4,4'-dimethylbiphenyl: were used as received from G.W. Griffin.154 1. Butyl azide: was prepared essentially by the method of Lieber, Chao, and Rao.155 To a mixture of 27 grams of sodium azide in 450 ml of methyl carbitol and 75 ml of water was added 60 grams of butylbromide in one batch and heated to 950 for 24 hours. The butyl azide was collected by distillation from the reaction mixture. m. 2-(4-pffluoropheny1)-A1-pyrroline: was synthesized by the method of Starr, Bulbrook, and Hixonlss. p-Fluorophenyl magnesium bromide (prepared from magnesium and Effluorobromo- benzene) in ether was refluxed and y-chlorobutylonitrile was added and refluxed four hours. The mixture was heated and xylene added dropwise while the ether distilled. When the temperature reached 1000 the reaction was cooled, the magnesium complex was decomposed with 50% sodium hydroxide, and the salts were extracted with ether. The ether extract was extracted with 4N hydrochloric acid. The resulting aqueous layer was neutralized with ammonium hydroxide and then extracted with ether. The ether layer was dried and distilled. 141 n. 2,5-dimethyl-2,4-hexadiene: (Chemical Samples Co.) Crystals which had sublimed to the top of the bottle upon sitting in the refrigerator were scraped out and used without further purification. o. N-methylpiperidine: (Aldrich) was distilled at atmospheric pressure and the center cut collected. Ketones: a. BenZOphenone: (Eastman white label) was recrystal- lized from ligroin twice. b. Acetophenone: (Matheson Coleman and Bell) was distilled under reduced pressure and the center cut retained. c. ValerOphenone: was prepared by the Friedel-Crafts acylation of benzene by valeryl chloride. The acid chloride was dissolved in a 15 fold excess of benzene and a 10% excess of anhydrous aluminum chloride added. The reaction was allowed to stir overnight. It was then poured into ice water, acidified to a clear solution, and extracted with ether which was dried and distilled. The ketone was passed through alumina and subsequently redistilled. d. Butyrophenone: (Aldrich) was purified by Dr. Irene Kochevar in 1970. e. pfAzidoacetophenone: was prepared by the method of Bader, Hansen, and McCarty.157 15 grams of pffluoroaceto- phenone was added to 30 cc of dimethylsulfoxide and a 10% excess of sodium azide. The mixture was heated to 80-900 for 24 hours and then poured into chloroform and extracted three times with saturated sodium chloride. The chloroform layer 142 was dried and evaporated. The crude ketone was dissolved in pentane and chromatographed on an alumina column. The material obtained crystallized upon standing and was recrystal- lized twice from ethanol, mp. 430 (lit. 44°). Six grams of material corresponding to a 30% yield were obtained. f. y-Azidobutyrophenone: To an equivalent amount of y-chlorobuterphenone was added ethylene glycol plus a catalytic amount of pftoluenesulfonic acid in four equivalents of benzene. The flask was fitted with a Dean-Stark trap and the solution refluxed several days and evaporated. The obtained oil was added to dimethylformamide and a 10% excess of sodium azide was added. This mixture was heated to 800 for 24 hours and worked up as described in "e". After evaporation of the chloroform the azidoketal was added to a 50:50 mixture of tetrahydrofuran and 0.2N hydrochloric acid. The mixture was stirred two days and then made neutral with ammonium hydroxide. The solvent was evaporated and the remaining water solution extracted with ether. This was dried, evaporated, and distilled. ffluaketone was redistilled and passed over alumina to remove any imino or aminoketone present. A 50% yield based on y-chlorobutyrophenone was realized. 9. G-Azidovalerophenone: To 25 grams of 6-chloro- valerylchloride infive times the equivalent amount of methylene chloride a 1.1 equivalent of aluminum chloride was added an equivalent of benzene. This mixture was reacted and worked up as in "c". To the formed d-chlorovalerOphenone (once distilled and recrystallized) dissolved in 143 dimethylformamide was added a 10% excess of sodium azide. The reaction was completed and worked up as in "e”. The material, after being passed over alumina, was dissolved in hexane twice and cooled. The hexane was poured off and the crystals collected while cold. The oil was dried under vacuum several days. Based on d-chlorovalerophenone, a 50% yield of the azidoketone was realized. h. e-Azidohexanophenone: Phenylmagnesium bromide was prepared by the action of bromobenzene on magnesium turnings in ether. To this formed grignard reagent was added one equivalent of 6-chlorocapronitrile and the solution was refluxed for four hours. The reaction was poured onto ice cubes containing three equivalents of hydrochloric acid and the ether layer was quickly separated. The acid layer was heated on a steam bath for one hour and extracted with ether which was dried and distilled. The e-chlorohexanophenone was recrystallized once from hexane and reacted with sodium azide as in "g". The azidoketone was recrystallized twice from hexane. Based on e-chlorohexanophenone a 55% yield was realized. 1. 6-Thiocyanonatovalerophenone: G-chlorovalerophenone was added to dimethylformamide. A 10% excess of potassium thiocyanonate was added and the mixture heated to 80° for 24 hours and worked up as in "e". The ketone was vacuum distilled and recrystallized twice from hexane. A 30% yield was realized j. N-methyl-4-methyl-4-benzoylpiperidine: N-methyl-4— cyanopiperidine was prepared essentially by the method of 144 Grob and Renk.158 Forty grams of isonipecotamide (Aldrich) dissolved in 150 cc of methanol was added all at once to 25 cc of 40% formalin and stirred for four horus at room tempera- ture. This mixture was then added to Raney Nickel (50% suspension in water; dry powder does not work) and hydrogenated on a Parr apparatus at 60 psi. After three hours at room temperature the hydrogen uptake stopped and the solution was filtered, evaporated, and titrated with acetone. The white amide was collected and dried (76% yield). Fifty grams of the amide was added to 300 cc of chloroform and 200 cc of thionyl chloride was slowly added. This solution was refluxed until all the material had dissolved and the solution was light brown in color. The excess thionyl chloride was evaporated and the brown oil neutralized with ammonium hydroxide. This solution was extracted with chloroform and the chloroform solution was dried and distilled. A 50% yield of the nitrile was obtained. Sodium sand159 was prepared by adding 29 grams of cleaned sodium to 400 cc of xylene and this mixture heated to reflux and stirred. The resulting sand was recovered by pouring off the xylene and washing the sand twice with dry benzene. To this sodium under nitrogen was added 150 cc of benzene and then 9 grams of chlorobenzene at 40°. When the exothermic reaction had subsided 50 grams of chlorobenzene was added dropwise at 30-400 and stirred six more hours. This mixture of phenyl sodium was then cooled to 50 and 41 grams (2/3 theoretical) of the nitrile was added at 5-80. 145 The mixture was stirred one hour longer and then 56 grams of methyl iodide (theoretical amount) was added at 8-100, and the mixture was stirred one hour longer. Twelve cc of ethanol was added followed by 200 cc of water and the reaction mixture was subsequently filtered through Celite and the benzene layer collected. The water layer was extracted several times with ether and these washings were added to the benzene layer which was dried over anhydrous magnesium sulfate ,filtered, and distilled. The residual oil was dissolved in ether and hydrogen chloride gas bubbled into the solution until precipitation no longer occurred. The hydrochloride of the alkylated nitrile was recrystallized twice from iSOprOpanol. Based on the unalkylated nitrile a 75% yield was obtained. Thirty grams of the alkylated nitrile was added to 0.660 moles (four times equivalent) of phenylmagnesium bromide (prepared as described in "h") whereupon a white precipitate formed. The reaction was refluxed eight hours after which 50% sodium hydroxide was added until reflux ceased. The layers were separated and the magnesium salts were extracted with chloroform and combined with the ether solution which was dried and distilled. This material proved to be the imine which was then added to 4 N hydrochloric acid and heated on a steam bath for one hour. The solution was neutralized with ammonium hydroxide and extracted with ether which was dried and evaporated. This aminoketone was added to ether and hydrogen chloride gas bubbled into the solution until 146 precipitation ceased. The hydrochloride salt was collected and recrystallized twice from methanol-butanone(75% yield based on alkylated nitrile). For use in photochemical studies the hydrochloride salt was added to a minimum amount of water, and 4N sodium hydroxide was added until the solution was alkaline. The solution was extracted with ether which was dried over anhydrous magnesium sulfate, filtered and evaporated. The ketone was dried under vacuum. k. N—benzyl-4-methyl-4-benzoy1piperidine: N-benzyl-4- methyl-4-cyan0piperidine‘wasprepared by the reported method of Kuhnis and Denss.161 Fifty grams of isonipecotamide were added to 285 cc of 3-pentanone and heated to reflux. To the boiling solution was added 66 grams of sodium carbonate and a pinch of potassium iodide. Benzyl bromide (one equivalent: 67 grams) was added dropwise and this mixture was refluxed four hours. The solution was filtered while hot, and the filtrate was washed several times with hot acetone. This solution was allowed to cool and the benzylamide collected by evaporation of the ketone mixture. The solid was recrystal- lized twice from ethanol-ether (82% yield). The amide was reacted with thionyl chloride as in "j". After distillation the nitrile was added to ether and hydrogen chloride gas added until precipitation ceased. The solid was collected and recrystallized twice from methanol-butanone (80% yield based on amide). 147 An equivalent amount of bromobenzene was added to 12 times its amount of ether and an equivalent of lithium metal was added all at once. The solution was refluxed for 28 hours and then an equivalent of triphenylmethane, dissolved in four times its amount of 1,2-dimethoxyethane, was added and stirred 20 minutes. The solution was then cooled in an ice-salt bath and the N-benzy1-4-cyanopiperidine added. The resulting solution was stirred ten minutes more, and an equivalent of methyl iodide was then added. The mixture was stirred 1% hours longer and then five equivalents of water were added and the solution evaporated. The resulting water solution was extracted several times with ether which solution was extracted four times with 4N hydrochloric acid. The acid solution was neutralized with ammonium hydroxide and extracted with chloroform which was dried and distilled to yield a 37% yield of the alkylated nitrile. This material was dissolved in ether and hydrogen chloride gas added. The precipitate was collected and recrystallized two times from isopropanol. The alkylated ketone was made from this nitrile as indicated in "j" except that only 2.5 equivalents of the Grignard reagent were used and a white precipitate did not form. Again the imine was isolated. This time the hydro- chloride salt had been made before this was realized and the imine was not isolated (methanol-butanone solution of imino- hydrochloride turned red upon heating). This hydrochloride was neutralized with sodium hydroxide which solution was extracted with ether. The ether was evaporated and the 148 material added to 4N hydrochloric acid and heated on a steam bath for an hour. This solution was extracted with ether which was dried and evaporated. The hydrochloride salt was remade and recrystallized two times from methanol-butanone (70% yield based on alkylated nitrile before spilling sample). The free base of the ketone was made as in "j". l. Rathke's Base Method: (a) To 7.05 grams of afi1 isopropylcyclohexylamine in four times its volume of THF in ’ a three-necked flask fitted with a nitrogen inlet valve and a septum cap was added 20 cc of 2.5M butyllithium. This was stirred under nitrogen for several minutes, then cooled to -70°C. Ten grams of the appropriate nitrile was added and this solution stirred 20-25 minutes. The solution was poured into a cooled addition funnel and added dropwise to 8.8 grams of methyl iodide in 30 cc of DMSO (dried over calcium hydride). This was stirred about an.hour and evaporated. Water was added and the solution extracted with ether which was dried, evaporated, and distilled. A nitrile mixture of about 60:40 alkylated to non-alkylated (NMR analysis) material was obtained. (b) To di-isopropylamine in four times its volume of THF was added an equivalent of n-butyllithium. This was cooled to -70°C. and the N-methyl-4-benzoylpiperidine dissolved in two times its amount of DMSO was added. This was stirred about an hour and then an equivalent of methyl iodide in THF was added. After stirring for about one-half hour the solution was evaporated and water added. The water solution was extracted with ether which was dried, filtered, and 'evaporated. A mixture of ketones containing about 30% 149 alkylated material (NMR analysis) was obtained. m. Phenyl-(N-methyl—4-methyl-4-piperidinemethanol)g To 0.5 grams of N-methyl-4-methyl-4-benzoylpiperidine in 20 cc of ethanol was added 1 gram of sodium borohydride. The solution was stirred four hours at room temperature and the ethanol evaporated. The white solid was stirred in water, which was made slightly acidic and extracted with ether. The ether solution was dried and evaporated. The alcohol obtained melted at 105-90. n. l-Methylcyclohexylphenyl ketone: Cyclohexane- carboxamide was prepared essentially by the method of 162 To 100 cc of chilled concentrated ammonium Baumgarten. hydroxide was added 50 grams of cyclohexanecarbonyl chloride over a period of one hour. The formed cyclohexanecarboxamide was isolated by filtration. To a solution of 25 grams of the dried amide in 150 cc of chloroform was added 100 cc of thionyl chloride. The mixture was refluxed 16 hours, followed by distillation of the chloroform and thionyl chloride at atmos- pheric pressure. The formed cyclohexylnitrile distilled at 95-70 at water aspirator pressure. To a solution of phenyl sodium (prepared from 8 g of sodium sand and 20 g of chlorobenzene as indicated in "j".) was added 13 grams of cyclohexylcarbonitrile at 5-80. After stirring for one hour, 24 g of methyl iodide were added at 5-80, and the mixture was stirred for 8 hour longer. Four cc of ethanol and 60 cc of water were then added. The mixture was filtered through celite, the benzene layer separated, 150 and the water layer extracted with ether. The ether washings were combined with the benzene layer which was dried and distilled. The l-methylcyclohexylcarbonitrile distilled at 960 at water aspirator pressure. A 50% yield based on the acid chloride was obtained. To 0.15 mole of phenyl magnesium bromide in ether (prepared from 3.6 grams of magnesium and 24 grams of bromobenzene) was added 0.1 mole of the l-methylcyclo- hexanecarbonitrile. The solution was refluxed seven hours and worked-up as in "h". The ketone distilled at 850 and a 50% yield based on starting nitrile was realized. The crude ketone (10 g) was added to 3.5 grams of hydroxylamine hydrochloride dissolved in 67 cc of 95% ethanol and 137 cc of 7% aqueous sodium hydroxide. The solution was refluxed 5 hours and cooled. The white crystalline needles were collected and recrystallized from ethanol twice. The oxime melted at 145-7°. This material was added to 80 cc of 12% aqueous hydrochloric acid and refluxed two hours. After cooling the water solution was extracted with ether which was dried and evaporated. The l-methylcyclohexylphenyl ketone distilled at 97-1000 at 0.03 mm Hg. Physical and Spectral Data for Synthesized Materials and Isolated Photoproducts: The physical and spectral data for the synthesized materials and isolated photoproducts used in this thesis are listed in Table XV. The following is the key to the Table: Physical Properties mp melting point bp boiling point at specified pressure 151 Infrared: NMR: -8- carbonyl s—singlet -N3 azide d-doublet -CN cyano t-triplet -C=NH imino m-multuplet -SCN thiocyanate -8N- amide -NH amine or imine -OH hydroxyl UV: wavelength in nm followed by extinction coefficient All NMR spectra were obtained in deuteriochloroform or carbon tetrachloride using TMS as standard. All shifts are in 6 units and the number of protons producing the indicated signal are shown. The piperidine ring protons are not indicated. The IR spectra were obtained neat or in nujol. 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K 3 More 02 09 cm a a: ._ _ .1 ._ P 44 _— _ _ mo_ nm_ NF ¢_X mo_ Aqrsuaqur enrqetex 174 4 60 1 40r 4000 5500 5000 2500 2000 1500 Cm '1 ~ .1 ‘ fl .1 (b2 .N (D and .5 OJ r0 C) Figure XL: IR Spectrum (top) and NMR Spectrum (bottom) of c-azidohexanophenone mcocmnmocmxmnoowwmuo mo Eouuommm who: "qu whomHm m\E .09 Om— . p - 175 Z; :__ fl _ :. . . j: ___. E: .. mm: mt Nu mo— 176 80; 60~ 40 20» 4000 5500 5000 2500 2000 1500 cm'l. } é ; 6 a 4 3' 2' 1 O 6 Figure XLII: IR Spectrum (top) and NMR Spectrum (bottom) of 6-thiocyanatovalerophenone Om moccmnmou0Hm>oumcm>00wno1c mo 0\E 09 09 Eouuowmm who: ”HHHax whomflm 00m 4;. _J:. 177 ...ww « dd mm mg 1 7 7 n _ E .21.. a a _n_ : m9 178 1 1 L L _1 4000 5500 5000 2500 2000 1500 cm‘1 W151 .1 q q q u (1)- \1-1 03w 0‘ .5 OJ N C) Figure XLIV: IR Spectrum (top) and NMR Spectrum (bottom) of N-methyl-4-methy1-4-benzoy1piperdine xooH m mm mcw>umm Hm comumnuw3 ocmowuomHmHMONcmnlv1awnumfilv1amcumelz mo Ennuoomm mzz UmH pmamooomp cououm muoumnmmfime 800m ">Ax madman L . fl a 2» x001. 3rd _ v.0 N mwi _2 Nd? 179 ohm mm m.mON mcflpfluomme>0wcmn1e1H>£u081¢1amnumelz mo Eduuommm 0\E OO_ 09 . who: uH>Ax whooflm 00m 180 q Ow ~421 _ ~ ,— em mo— N: :u :— : RIM NON 181 60* 20* 4000 5500 5000 2500 2000 1500 cm' 80" l 60 40” L 1 1 11 i 21 2000 1800 1600 1400 1200 1000 800 cm- Figure XLVII: IR Spectrum of 2-methyl-S-methyl-G-phenyl-2- azabicyclo [3.1.3 hepta-6-ol: Top (neat), Bottom (in nujol) H01m1mum0n H4 .8 odomownmNo 1w1wmcocd1m1Hmc0021m1wscpoE1w mo eonoooom mzz ”HHH>qx madman e m 0 PF Lll )Illilhfblb I. I E l k 1111411 I11 4 1 In 44441.1: .11 11.114 182 HOImIMuQms Hna.m_oHo>0HnmNm 1N1H>cmsm1o1amnume1m1am£umelm mo Eduuowmm mom: ”xHAx muomflm 0\E 0o 09 OON 183 ; .1 a i _ _ 2:7 1: . a: a. . ___.____ _ 09 m9 O— O: 184 801* 60’ I 20 L l l L l l 4000- 3500 3000 2500 2000 1500 cm J r '5 7 6 5 3 5 2 1 0 5 Figure L: IR Spectrum (top) and NMR Spectrum (bottom) of Phenyl-N-methyl-4-methylpiperidinemethanol Om r HocmnumemcHUHH0QHQH>£u081o1H>£ume121amcmnm mo Edupommm mmmz “HA whomem m\E OO— 8 00w P — 185 £3 1_ t ‘— ON. a _ we _ _ = I. is m: 1 «~w— ‘ .q ._ A34. mv_ 9N 186 8O " 60“ 46»- f W 1 i L i 1 1 4000 3500 3000 2500 2000 1500 cm'1 L4 ‘_ _h k‘ 1;...1 __L‘ J V‘ ~v— ‘i 'v T ' T v—r V I fr 1 0 00+ r, 0‘ a. b (N N Figure LII: IR Spectrum (top) and NMR Spectrum (bottom) of N-benzyl-4-methyl-4-benzoylpiperidine 187 mcepeummflmaacucwn1vlamnumelvlahwcwnlz mo Eduuommm mmmz ”HHHA ousmmm 6? 09 one 8w Omw . _ _m J .1? _ :7: J—‘w.~ « 1 . - Sq _u _1 # mflm mom wwe mo— aml NON t . mo. 188 I II III IV I | m m c o o. m m H O 2 4 6 8 10 min Figure LIV: VPC Trace for l-methylcyclohexylphenyl Ketone (IV); Benzene (I), Octadecane (II), Type II Product (III) AHHV Honooamamomo AHV momewomuuwe momuw> momu0> AHV 00>:0onNcmm mo AHvacocmcmoumom mo mammamc¢ mammamc¢ new momufi um> HMUHQmB « uH>q whomflm How momma um> Hmowmwe 4 ">4 wusmflm CH8 0. m o a. N 0 see 0 v N O a 5 a a q q q d ] a -..—....-- —- -..—— .....- ___,— 189 H H -. .. — ...—.... ___. _.-—..— 190 A>HV momemomuoo .AHHV uooooum HH mama .AHV encapsunmmz aAHHHVochHHmQHmH>0wc0b1o1a>nume1v1amzums1z mo momma um> ”HH>A musmwm use 9 m o . a. >H HHH 191 Part III Experimental Data Photoreduction and Emission Studies: The data of the following section are arranged according to quencher studied. The first number in the heading is the ketone concentration and all studies are in benzene unless otherwise noted. In the photoreduction studies the per-cent conversions are indicated and Abss-Abs is the absorbance of the standard solution(s) minus the absorbance of the specific solution. In the phosphorescence studies the conditions are given as follows: scale, high voltage setting, sensitivity setting. The wavelength of irradiation is the last number mentioned and the emission wavelengths were always at 450 and 480 nm. The reproducibility of the photoreduction studies is about 15%. Comparison of two or three solutions of the same composition were made and any solution which deviated by more than 4% from the others was discarded. Reproducibility in the phosphorescence is on the order of 18%. Any deviation between two solutions greater than 5% caused those solutions to be repeated. Standard deviations for each quenching run are indicated after the calculated ktr value. 192 BENZOPHENONE, NAPHTHALENE QUENCHER 0.054 K in 0.5 M isoprOpanol 40% conversion 0.054 K in 0.5 M iSOprOpanol 59% conversion Quencher Avg Abs 4 Quencher Avg Abs 4 Cone (M) Abs -Ab§ °/¢ Conc (M) Abs -Ab§ O/¢ S 0.534 --- --- S 0.581 --- --- 0.00 0.292 0.242 1.00 0.00 0.264 0.317 1.00 0.000109 0.364 0.170 1.42 0.000109 0.363 0.218 1.45 0.000218 0.398 0.136 1.77 0.000218 0.417 0.164 1.93 0.000328 0.434 0.100 2.42 0.000327 0.451 0.130 2.46 0.000437 0.448 0.086 2.81 0.000436 0.474 0.107 2.95 kt‘t=4300i296 ktr =4333il35 0.054 K in 0.5 M isopropanol 0.054 K scale .1 HV 720 100 31% conversion Phosphorescence Ex 375 Em 450,480 Quencher Avg Abs 4 /¢ Quencher Cor. 4 / ¢ Conc (M) Abs -Ab§ O Conc (M) Reading, 0 S 0.627 --- --- 0.00 51 1.00 0.00 0.432 0.195 1.00 0.00000525 43 1.19 0.000118 0.499 0.127 1.53 0.0000105 36.5 1.40 0.000236 0.527 0.100 1.94 0.0000158 31 1.64 0.000355 0.544 0.082 2.37 0.0000210 27 1.89 0.000474 0.564 0.062 3.14 0.0000260 24 2.12 ktr =4212i29l ktr =40,000i2326 0.02 K scale .3 HV 900 80 Phosphorescence BX 366 in 1M C6H12 Em 450,480 Quencher Cor. 4 /¢ Conc (M) Reading 0 0.00 57 1.00 0.0000208 45.7 1.26 0.0000416 39.8 1.44 0.0000624 34 1.67 0.0000832 28 2.02 kt T=1l,518:861 193 BENZOPHENONE, BIPHENYL QUENCHER 0.054 K in 0.5 M isopropanol 31% conversion 0.054 K in 0.5 M isopropanol 27% conversion Quencher Avg Abs 4 Quencher Avg Abs 4 Conc (M) Abs -Ab§ °/¢ Conc (M) Abs -Ab§ °/¢ 8 0.627 --- --- S 0.671 --- --- 0.00 0.432 0.195 1.00 0.00 0.488 0.184 1.00 0.00925 0.473 0.154 1.26 0.0101 0.533 0.138 1.33 0.0185 0.497 0.130 1.49 0.0203 0.553 0.118 1.62 0.0278 0.519 0.108 1.81 0.0304 0.568 0.103 1.78 0.0370 0.524 0.103 1.88 0.0405 0.582 0.089 1.97 k t=26.9il.74 t 0.02 K in 0.5 M isoprOpanol 59% conversion Quencher Avg Abs 4 Conc (M) Abs —Ab§ °/¢ S 0.972 -—- --- 0.00 0.398 0.573 1.00 0.0101 0.598 0.373 1.54 0.0203 0.672 0.300 1.92 0.0304 0.718 0.254 2.44 0.0405 0.776 0.195 2.94 kt? =49:2.8 k 't=28.2i3.4 t 0.02 K in 0.5 M iSOpropanol 42% conversion Quencher Avg Abs ¢ Conc (M) Abs -Ab§ 0/4 S 0.454 --- --- 0.00 0.267 0.187 1.00 0.0101 0.327 0.127 1.51 0.0203 0.359 0.095 1.97 0.0303 0.378 0.076 2.46 0.0405 0.391 0.063 2.98 ktr =49i1.0 0.0075 K in 0.5M isopropanol 0.054 K scale .1 HV 840 100 30% conversion Phosphorescence Ex 375 in 0.5M isopropanol Em 450,480 Quencher Avg Abs 4 /¢ Quencher Cor. 4 /¢ Conc (M) Abs -Ab§ ° Conc (M) Reading 0 S 0.915 --- --- 0.00 0.637 0.278 1.00 0.00 61.2 1.00 0.0101 0.749 0.166 1.68 0.0093 52 1.17 0.0203 0.798 0.117 2.38 0.0185 45.2 1.40 0.0304 0.821 0.094 2.94 0.0279 36 1.70 0.0405 0.839 0.076 3.65 0.0372 31.2 1.98 ktI =66.1:1.5 ktT =22.8i2.8 194 BENZOPHENONE, BIPHENYL QUENCHER (Continued) 0.054 K scale .3 HV 740 100 Phosphorescence Ex 375 0.035 K scale .3 HV 720 85 Phosphorescence Ex 375 Em 450,480 Em 450,480 Quencher Cor. 4o/¢ Quencher Cor. ¢0/4 Conc (M) Reading Conc (M) Reading 0.00 58.1 1.00 0.00 67.3 1.00 0.00926 28.8 2.06 0.00945 23.5 2.83 0.0186 22.5 2.71 0.0184 17.3 3.86 0.0278 16.7 3.86 0.0284 13 5.13 0.0370 12.7 4.28 0.0378 9.4 7.12 ktT =99.4i9.0 ktr=164i15 0.035 K scale .3 HV 720 85 0.021 K scale .3 HV 720 90 Phosphorescence Ex 375 Phosphorescence Ex 375 Em 450,480 Em 450,480 Quencher Cor. 4 /¢ Quencher Cor. ¢ Conc (M) Readiagi 0 Cone (M) Reading 0/4 0.00 65.9 1.00 0.00 74.3 1.00 0.005 39.5 1.67 0.00103 64 1.16 0.010 29 2.27 0.00205 55.5 1.33 0.015 20.5 3.20 0.00308 47 1.58 0.020 18 3.66 ktr =135i5.9 ktr =168113 0.025 K scale .3 HV 720 80 Phosphorescence Ex 375 Em 450,480 Quencher Cor. ¢ Conc (M) Reading» 0/4 0.00 87 1.00 0.00503 36 2.42 0.0101 21 4.14 0.0151 17 5.12 0.0201 13 6.70 kt 1:288ill.6 0.0075 K scale .3 HV 730 87 Phosphorescence Ex 375 EM 450,480 Quencher Cor. ¢ Conc (M) Reading 0/4 0.00 67.5 1.00 0.00016 54.8 1.22 0.00033 47.3 1.41 0.00050 39.6 1.69 0.00068 35.8 1.88 ktT=1323i55 BENZOPHENONE, 195 4-CHLOROBIPHENYL QUENCHER 0.053 K in 0.5 M isopropanol 26% conversion 0.035 K in 0.5 M isopropanol 30% conversion Quencher Avg AbsS 4 /¢ Quencher Avg Abs 4 /¢ Conc(M) Abs -Abs 0 Cone (M) Abs -Ab§ 0 S 0.670 --- --- S 0.614 --- --- 0.00 0.496 0.174 1.00 0.00 0.431 0.183 1.00 0.0101 0.607 0.063 2.77 0.000512 0.444 0.170 1.08 0.0202 0.619 0.051 3.42 0.00102 0.467 0.147 1.25 0.0303 0.640 0.030 5.82 0.00154 0.483 0.131 1.40 0.0403 0.648 0.022 7.93 0.00205 0.492 0.122 1.50 ktI =157 :18 ktT =226i35 0.054 K in 0.5 M isopropanol 0.054 K in 0.5 M isopropanol 22% conversion 30% conversion Quencher Avg Abs 4 Quencher Avg Abs 4 Conc (M) Abs -Ab§ °/¢ Conc (M) Abs -Ab§ °/¢ 8 0.591 --- --- S 0.638 --- --- 0.00 0.461 0.130 1.00 0.00 0.456 0.182 1.00 0.00504 0.528 0.0627 2.07 0.00504 0.544 0.094 1.94 0.0101 0.542 0.0490 2.62 0.0101 0.566 0.072 2.54 0.0152 0.557 0.0337 3.84 0.0152 0.581 0.057 3.22 0.0202 0.561 0.0297 4.13 ktr =17Sil7 ktr =l65i22 0.035 K in 0.5 M iSOpropanol 0.054 K in 0.5 M isopropanol 21% conversion 29% conversion Quencher Avg Abs 4o/¢ Quencher Avg Abs ¢ Conc (M) Abs -Ab§ Conc (M) Abs -Ab§ o/4 S 0.866 --- --- S 0.491 --- --- 0.00 0.682 0.184 1.00 0.00 0.350 0.141 1.00 0.005 0.779 0.087 2.12 0.0101 0.443 0.048 2.98 0.010 0811 0.055 3.36 0.0202 0.453 0.038 3.78 0.015 0.821 0.045 4.09 0.0303 0.467 0.024 6.04 0.020 0.831 0.035 5.24 0.0403 0.474 0.017 8.60 ktt =220110 ktT =172120 BENZOPHENONE, 4-CHLOROBIPHENYL QUENCHER (Continued) 0.035 K in 0.5 M isoprOpanol 41% conversion Quencher Avg Abs 4 Cone (M) Abs -Ab§ °/¢ 8 0.454 --- --- 0.00 0.251 0.203 1.00 0.0101 0.385 0.069 2.96 0.0202 0.421 0.033 6.66 0.0303 0.429 0.025 6.66 0.0404 0.435 0.019 11.83 ktr =240i39 0.0075 K in 0.5 M isopropanol 29% conversion (20% conversion) Quencher Avg Abs 4 /¢ Conc (M) Abs -Ab§ ° S 0.977 --- --- 0.00 0.722 0.255 1.00 S 1.00 --- —-- 0.00 0.830 0.197 1.00 0.000992 0.806 0.171 1.49 0.00198 0.845 0.132 1.94 0.00291 0.923 0.0767 2.59 0.00388 0.933 0.0670 2.94 ktt =504iZl 0.02 K in 0.5 M iSOpropanol 40% conversion Quencher Avg Abs 4 Conc (M) Abs -Ab§ °/¢ S 0.425 --- --- 0.00 0.240 0.185 1.00 0.000512 0.272 0.153 1.21 0.00102 0.285 0.140 1.33 0.00154 0.302 0.123 1.51 0.00205 0.316 0.109 1.69 ktT =350r30 BENZOPHENONE, 197 3-CHLOROBIPHENYL QUENCHER 0.054 K in 0.5 M isopropanol 37% conversion Quencher Avg AbsS 00/4 Conc (M) Abs -Abs 8 0.599 --- --- 0.00 0.378 0.221 1.00 0.00538 0.448 0.151 1.46 0.0107 0.485 0.114 1.94 0.0161 0.506 0.0928 2.38 0.0215 0.525 0.074 2.99 ktt =87il.3 0.0083 K in 0.5 30% conversion M isopropanol Quencher Avg Abs 4 /¢ Conc (M) Abs -Ab§ o S 0.786 --- --- 0.00 0.552 0.234 1.00 0.0010 0.604 0.182 1.28 0.0020 0.625 0.161 1.46 0.0030 0.640 0.146 1.60 0.0040 0.656 0.130 1.80 k T =228i28 t 0.025 K in 0.5 M isopropanol 60% conversion Quencher Avg Abs 4 Cone (M) Abs -Ab§ °/¢ S 1.30 --- --- 0.00 0.911 0.387 1.00 0.00112 0.971 0.327 1.17 0.00224 1.01 0.288 1.33 0.00336 1.04 0.253 1.50 ktT=l49t2 BENZOPHENONE, 198 Z-CHLOROBIPHENYL QUENCHER 0.054 K in 0.5 M isopropanol 24% conversion 0.054 K scale .3 HV 740 80 Phosphorescence' Ex 375 Em 450,480 Quencher Cor. ¢ Conc (M) Reading 0/4 0.00 63.4 1.00 0.05 39.5 1.63 0.10 29 2.18 0.15 23.3 2.71 0.20 17 3.71 ktr =12.3i0.7 0.035 K scale .3 HV 720 90 Phosphorescence Ex 375 Quencher Avg Abs 4 /¢ Conc (M) Abs -Ab§ O S 0.601 --- --- 0.00 0.457 0.144 1.00 0.10 0.471 0.130 1.11 0.20 0.485 0.116 1.25 0.30 0.506 0.095 1.36 0.40 0.515 0.086 1.42 ktr =l.lSi0.08 0.035 K scale .3 HV 720 80 Phosphorescence Ex 375 Em 450,480 Quencher Cor. ¢ Conc (M) Reading o/4 0.00 63.8 1.00 0.05 43.6 1.46 0.10 29.5 2.20 0.15 19.2 3.30 0.20 16.3 3.90 ktT =12.8i2.2 0.021 K scale .3 HV 720 80 Phosphorescence Ex 375 Em 450,480 Quencher Cor. ¢ Conc (M) Reading 0/4 0.00 65.1 1.00 0.01 55.7 1.12 0.02 53.8 1.21 0.03 48.7 1.33 0.04 43.0 1.50 ktr =1l.5i0.8 Em 450,480 Quencher Cor. ¢ Conc (M) Reading 0/4 0.00 75.5 1.00 0.05 48.5 1.56 0.10 31 2.50 0.15 23.5 3.20 0.20 18 4.19 k T =14.2i1.5 t 0.0075K scale.3 HV 710 72 Phosphorescence Ex 375 Em 450,480 Quencher Cor. ¢ Conc (M) Reading 0/4 0.00 68.1 1.00 0.01 62 1.11 0.02 55.3 1.23 0.03 50.3 1.35 0.04 46.5 1.46 ktT=1l.4i0.2 199 BENZOPHENONE, 4-METHYLBIPHENYL QUENCHER 0.035 K scale .3 HV 800 85 0.025 K scale .1 HV 740 80 Phosphorescence Ex 366 Phosphorescence Ex 366 Em 450,480 Em 450,480 Quencher Cor. ¢ Quencher Cor. 4 /¢ Conc (M) Reading 0/4 Conc (M) Reading 0 0.00 64.2 1.00 0.00 59.9 1.00 0.00109 38.2 1.70 0.00052 44 1.35 0.00218 29 2.22 0.00104 32.8 1.83 0.00326 24.6 2.59 0.00208 20.7 2.50 0.00435 19 3.39 0.00311 18.9 3.17 ktr =560i36 ktr =722:38 0.0017 K scale .1 HV 720 70 0.0087 K scale .3 HV 790 80 Phosphorescence Ex 366 Phosphorescence Ex 366 Em 450, 480 Em 450,480 Quencher Cor. ¢ Quencher Cor. ¢ Conc (M) Reading o/¢ Conc (M) Reading o/¢ 0.00 62.7 1.00 0.00 79.8 1.00 0.00046 42.8 1.46 0.000143 49.5 1.41 0.00093 34.2 1.83 0.000286 43 1.85 0.0018 26 2.42 0.000427 34 2.06 0.0028 18.1 3.46 0.000572 26 2.70 ktT =890156 ktr =2823i171 0.0086 K scale .1 HV 740 70 Phosphorescence Ex 366 Em 450,480 Quencher Cor. ¢ Conc (M) Reading 0/4 0.00 65.8 1.00 0.00028 48.5 1.35 0.00057 29.2 2.76 0.00086 21.7 3.04 kt r=2237i657 200 BENZOPHENONE, Z-METHYLBIPHENYL QUENCHER 0.052 K scale .3 HV 800 85 0.0131 K scale .3 HV 780 80 Phosphorescence Ex 366 Phosphorescence Ex 366 Em 450,480 Em 450, 480 Quencher Cor. ¢ Quencher Cor. ¢ Conc (M) Reading o/¢ Conc (M) Reading o/¢ 0.00 50 1.00 0.00 66.1 1.00 0.00887 27.6 1.82 0.00887 39 1.69 0.0177 18.7 2.64 0.0177 24.3 2.74 ktt =92.5i0.2 ktr =88i10 201 Gas Chromatographic Studies: The data are arranged according to the ketone studied. The first number given in the heading is the ketone concentration which is followed by the concentration of the standard used. Any number in parentheses indicates the concentration of the standard used for that particular solution (if different from the concentration of standard used for the rest of the run). The following abbreviations are used: Act for actinometer; C6H12 for cyclohexane; pyr for pyridine; pipyl for piperylene; acph for acetOphenone; Prod/Std for product to standard ratios; conc for concentration. A11 actinometers were valerophenone using the same concentration of valerophenone as ketone. Acetophenone- gigfpiperylene was used as actinometer in the sensitization studies. Column conditions are listed in XVII. The reproducibility of the relative VPC peak areas and consequently of the concentrations of the major photoproducts is on the order of :5%. The quantum yields incorporate an additional :3% uncertainty in reproducibility because of the precision of actinometry. Errors in actinometry, either in the precision or accuracy, do not affect ktr since they cancel out in the ratio ¢o/¢ . The ktr values obtained by quenching acetophenone or benzaldehyde are reproducible to within 5%. 202 G-AZIDOVALEROPHENONE 0.1 K tetradecane 0.00405M 366 Column Conditions #1 Solvent Prod/Std 0 /® System Ratio 0 benzene 0.432 --- 50% Efbutanol 0.444 --- 0.5 M pyr. 0.802 --- 0.001 M Naph 0.457 --- 0.01M Naph 0.346 1.63 Act 0.482 —-— [Acph‘J 0.0035 0.07 K tetradecane 0.0068M 366 Column Conditions #1 Solvent Prod/Std System Ratio benzene 0.401 C6H12 0.321 Act(0.00394) 0.695 EAcphJ 0.0054 Column Conditions #1 0.1 K tetradecane 0.00457 366 Act Excpffl 0.07 K tetradecane 0.00197 366 Act 0.5M pyridine EAcplfl 0.05 K tetradecane 0.00442 366 Act 13¢le Column Conditions #1 0.1 K tetradecane 0.00457 313 Act CACPI 0.05 K tetradecane 0.00442 313 Act [309131 0.1 K tetradecane 0.00421 313 Column Conditions #1 SOIVOnt PYOG/Std ¢)/¢ Syjstvm __ l\¢lLi__(__)_F—.__ ‘____ - benzene 0.416 --- 0.001 diene 0.416 --- 0.002 diene 0.436 --- 0.003 diene 0.368 1.16 Act 1.42 --- [Acpri] 0.0035 Prod/Std ratios for irradiated times 8 hr 16 hr 24 hr 37.5 hr 0.211 0.352 0.479 --- 0.430 0.789 1.16 --- 0.0019 0.0032 0.0044 ' -—- 1.22 1.90 2.69 --- 2.70 4.18 6.06 --- 1.88 --- --- --- 0.0048 0.0075 0.0106 --- --- 0.447 --- 0.973 --- 1.08 --- 2.16 0.00395 0.0086 Prod/Std ratios for irradiated times 45 min 90 min 135 min 0.106 0.142 0.223 0.120 0.280 0.442 0.0010 0.0013 0.0023 --- --" 0.489 --- --- 1.09 --- --- 0.0043 203 G-AZIDOVALEROPHENONE (Continued) 0.07 K Piperylene sensitizee Column Conditions #2 Column Conditions #2 0.07 K piperylene sensitizee 1 Ratio .555 Pipyl Ratio ¢isc Pipyl trans 4 Conc. trans 36.9 0.202 1.38 0.101 0.072 0.98 18.5 0.125 1.21 Acph 0.073 12.3 0.0930 1.15 9.55 0.0684 1.11 36.9 (Acph) 0.0814 --- 19.1 0.149 1.25 9.23 0.0898 1.11 19.1 (Acph) 0.0538 --- 19.1 0.0931 1.21 9.0 0.0548 1.09 19.1 (Acph) 0.0311 ktr= 101:5 intercept 1.01 0.07 K l-methylnaphthalene quencher tetradecane 0.00405 366 Column Conditions #1 Quencher Prod/Std 4o Conc.(M) Ratio /¢ 0.00 0.488 1.00 0.0043 0.348 1.40 0.0065 0.307 1.59 0.0089 0.255 1.91 0.011 0.225 2.19 Act 1.10 [Acplil 0.004 ktT= 98.5:7.7 6-THIOCYANATOVALEROPHENONE 0.07 K tetradecane 0.00197 Column Conditions #1 313 Solvent Prod/Std System Ratio benzene 0.209 Act 33.5 [210ij 0.00082 2 BUTYROPHENONE 0.1 K tetradecane 0.00405 Butyl Azide Quencher 366 Column Conditions #1 Prod/Std 4 Quencher Conc (M) Ratio °/¢ 0.00 0.821 1.00 0.0394 0.586 1.38 0.0591 0.518 1.59 0.0788 0.469 1.79 0.0985 0.428 1.92 [_Acplfl o . 007 ktt=9.810.3 e-AZIDOHEXANOPHENONE Column Conditions #1 5 hr 0.1 K tetradecane 0.00410 366 Act D‘Acpfil 0.07 K tetradecane 0.00375 366 Act(0.00505) 0.5 M pyr(0.00375) 0.01 M 1-methy1naphtha- 1ene(0.00418) [Acplil 0.05 K tetradecane 0.0041 366 Act EACPE 0.07 K tetradecane 0.0041 1-methylnaphtha1ene quencher Column Conditions #1 366 04 0.07 K tetradecane 0.00429 2-(p—f1uor0pheny1)—A1- pyrroline quencher Column Conditions #1 313 Quencher Prod/Std 4 /¢ Conc (M) Ratio 0 0.00 1.59 1.00 0.00107 1.27 1.25 0.00214 1.03 1.54 0.00321 0.835 1.90 0.00428 0.694 2.25 [Acph'J 0 . 014 ktr=264121.5 0.409 0.377 0.0034 0.384 0.731 0.780 0.0029 0.260 0.237 0.0021 0.745 0.730 0.0061 0.787 1.46 0.0059 0.518 0.465 0.0042 Prod/Std Ratios for Irradiated Times 10 hr 15 hr 1.05 1.03 0.0086 1.10 2.17 0.370 0.0082 0.696 0.656 0.0057 0.07 K hexadecane 0.0227 Column Conditions #3 366 Quencher Prod/Std 4 /¢ Conc (M) Ratio 0 0.00 0.739 1.00 0.00174 0.639 1.16 0.00348 0.535 1.38 0.00522 0.510 1.45 0.00696 0.463 1.60 [Acple 0. 006 ktr=9317.9 fiztgge/Std Cyclobutanol Before-After(hu) Prod/Std 2.62 2.30 0.62 Act = 1.03 (0.00410) LE reacted =0.021 I:AZIDOBUTYROPHENONE Column Conditions #1 0.1 K tetradecane 0.00449 366 Act(0.00457) [Mph] 0.07 K tetradecane 0.00197 366 Act 0.5 M pyridine Umplfl 0.05 K tetradecane 0.00422 366 Act EACPEI 0.03 K tetradecane 0.00396 366 Act CACplfl 0.1 K tetradecane 0.00449 313 Act(0.00457) EACpli] 0.1 K tetradecane 0.00422 313 Column Conditions #1 Quencher Prod/Std Conc (M) Ratio 0.00 0.095 Act 2.94 [11ch 0.0008 0.07 K tetradecane 0.00422 313 Column Conditions #1 Quencher Prod/Std Conc (M) Ratio 0.00 0.0861 Act 2.88 [hcplil 0.00073 205 Prod/Std Ratios for Irradiated Times 24 hr 56 hr 64 hr 72 hr 0.0113 0.0278 --- 0.0345 1.55 3.04 --- 4.20 0.0001 0.00025 --- 0.00031 0.0647 0.147 --- 0.190 6.07 29.82 31.87 33.50 --- --- 0.358 —-- 0.00025 0.00058 0.00075 --- 0.0255 --- 0.0539 --- 1.81 --- 4.09 --- 0.00022 0.00046 --- 0.0177 --- 0.0237 --- 1.07 --- 1.55 0.00014 0.00019 4 hr 8 hr 16 hr 0.025 0.0696 0.116 1.40 2.50 3.79 0.0002 0.00063 0.0010 0.1 K tetradecane 0.00422 366 Column Conditions #1 Quencher Prod/Std Conc (M) Ratio 0.00 0.0144 Act 1.64 0.5 M pyr 0.426 [Acplil 0.00012 0.07 K tetradecane 0.00422 366 Column Conditions #1 Quencher Prod/Std Conc (M) Ratio 0.00 0.0121 Act 0.960 [—11ch 0.00010 0.00(0.00359) 0.036 C6H12(0.00505)0.0195 Act (0.00375)3.06 ['21ch 0.00026 206 I:AZIDOBUTYROPHENONE (Continued) 0.07 K tetradecane 0.000506 l-methylnaphthalene quencher acetophenone 366 Column Conditions #1 Quencher Prod/Std 4 0.07 K octadecane 0.00555 1-methy1naphthalene quencher 366 Column Conditions #4 2-phenylpyrrole Quencher Prod/Std 40 Conc(M) Ratio °/¢ 0.00 0.405 1.00 0.0493 0.279 1.45 0.0986 0.210 1.93 0.148 0.138 2.93 0.197 0.117 3.46 @cplj 0.00041 ktr=11.0i1.7 0.07 K Piperylene Sensitizee Column Conditions #2 366 1 Ratio .555 Pipyl trans 4 4.93 0.0354 1.60 6.58 0.0583 1.96 19.72 0.0826 2.72 4.93(Acph) 0.0559 --- ktT=l7i1 intercept=l.26 0.033 K tetradecane 0.00422 366 Column Conditions #1 Quencher Prod/Std Conc (M) Ratio 0.00 0.0121 Act 0.960 [Acpljl 0. 0001 Conc (M) Ratio /¢ 0.00 0.0846 1.00 0.0493 0.0553 1.52 0.0986 0.0347 2.43 0.148 0.0427 1.98 0.197 0.029 2.91 [Pyrrole'l 0.0014 ktt=1012.3 0.07 K Piperylene Sensitizee Column Conditions #2 366 1 Ratio .555 Pipyl trans 4 4.92 0.0567 1.73 6.56 0.0711 1.89 9.84 0.109 2.13 4.92 (Acph) 0.0951 --- ktt=l3il intercept=l.25 0.07 K piperylene Sensitizee 366 Column Conditions #2 Pipyl Ratio 4. Conc (M) Trans 13C 0.201 0.0291 0.72 Acph 0.0395 207 I:AZIDOBUTYROPHENONE (Continued) 0.1 K Octadecane 0.0079, Tetradecane 0.00449 Column Conditions #4 313 Compound Prod/Std Ratios for Irradiated Times 0.00 hr 4 hr 8 hr 16 hr cyclic imine 0.00 0.0992 0.142 0.162 Pyrrole 0.00 0.475 0.698 0.798(3:1) Parent ketone 5.80 4.16 3.35 2.26 Act 0.00 1.414 2.78 4.09 [K] reacted 0.00 0.022 0.032 0.047 0.1 K Octadecane 0.0079, Tetradecane 0.00449 Column Conditions #4 366 Compound Prod/Std Ratios for Irradiated Times 0.00 hr 30 hr 60 hr 90 hr cyclic imine 0.00 0.0886 0.115 0.121 Pyrrole 0.00 0.276 0.326 0.568 (2.5:1) Parent ketone 5.80 4.77 4.11 3.97 Act 0.00 1.58 3.09 4.28 [K] reacted 0.00 0.019 0.031 0.034 N-METHYL-4-METHYL-4-BENZOYLPIPERIDINE 0.04 K tetradecane 0.00507 0.04 K tetradecane 0.00507 313 dodecane 0.00876 313 nonadecane 0.00459 Column Conditions #5 Column Conditions #6 Mercaptan Prod/Std Solvent Prod/Std Conc (M) Ratio System Ratio 0.00 0.133 benzene 0.0966 0.0154 1.26 0.5 M pyr 0.0285 Act 3.07 3.07 A [BenzaldehydEl 0 . 002 Eyclobutanoi} 0 . 00074 208 N-METHYL-4-METHYL-4-BENZOYLPIPERIDINE(Continued) 0.04 K tetradecane 0.00464 313 dodecane 0.00547 Column Conditions #5 Mercaptan Prod/Std Conc (M) Ratio 0.0104 0.106 Act 0.428 Benzaldehyde“! 0 . 0012 0.04 K decyl alcohol 0.00423 l-methylnaphthalene quencher Column Conditions #5 313 Quencher Prod/Std 4o Conc (M) Ratio /¢ 0.00 0.154 1.00 0.00199 0.105 1.47 0.00399 0.0830 1.86 0.00597 0.0745 2.07 0.00796 0.0698 2.26 [Benzaldehyde—I o . 001 ktr=250 initially;curves downward 0.04 K Piperylene Sensitizee Column Conditions #2 313 1 Ratio .555 Pipyl trans 4 5.03 0.0508 5.28 2.51 0.0315 4.74 1.25 0.0198 3.63 0.84 0.0138 2.72 0.63 0.0114 2.56 0.50 0.0094 2.21 5.03(Acph)0.101 Intercept tending to 1.00 plot curves downward 0.04 K Octadecane 0.00449 Naphthalene quencher 313 Column Conditions #6 Quencher Prod/Std Ratio Conc (M) Cyc. Ketone 0.0008 0.261 2.34 0.008 0.481 2.98 0.08 0.703 3.57 [Cyclobutanol] 0 . 0029 0.04 K tetradecane 0.00331 313 decyl alcohol 0.00423 Column Conditions #5 Dodecyl mercaptan 0.0199 1-methy1naphthalene quencher Quencher Prod/Std 4 /¢ Conc (M) Ratio 0 0.00 0.503 1.00 0.00199 0.343 1.47 0.00399 0.268 1.88 0.00597 0.192 2.62 0.00796 0.156 3.22 Act 1.125 --- EBenzaldehydé] 0.003 kt1=251124 0.04 K Piperylene Sensitizee Column Conditions #2 313 1 Ratio .555 Pipyl trans 4 5.03 0.214 2.97 2.40 0.120 2.95 2.00 0.0653 2.86 1.60 0.0477 2.67 1.20 0.0385 2.50 0.80 0.0325 2.38 0.40 0.0289 2.24 1.20(Acph) 0.127 0.20 0.0192 1.79 0.158 0.0180 1.46 0.20(Acph) 0.317 intercept tending to 1.00 k+r=0.2 209 N-METHYL- 4-METHYL-4-BENZOYLPIPERI DINE (Cont inued) 0.04 K Octadecane 0.00409 Tetramethylbutadiene quencher Column Conditions #3 366 0.04 K octadecane 0.00402 Tetramethylbutadiene quencher Column Conditions #3 366 Quencher Prod/Std 4 /¢ Conc (M) Ratio ° 0.500 0.75 1.00 1.00 0.665 1.13 2.00 0.598 1.25 3.00 0.510 1.47 5.00 0.492 1.52 6.00 0.453 1.66 7.00 0.319 2.35 [Cyclobutanol] 0 . 0077 Quencher Prod/Std Conc (M) Ratio 0.00 0.196 0.0403 0.510 0.0806 0.582 0.161 0.630 0.242 0.634 0.322 0.649 0.403 0.653 0.405 0.646 0.810 0.662 1.22 0.634 1.62 0.629 0.04 K Octadecane 0.00436 Naphthalene Quencher Column Conditions #3 313 Quencher Prod/Std Conc (M) Ratio 0.0312 0.0804 0.0624 0.112 0.0936 0.174 0.125 0.205 0.156 0.236 [Cyclobutanofl 0 . 0 00 9 0.04 K Tetradecane 0.00477 313 Octadecane 0.00397 Column Conditions #6 Dodecyl Mercaptan 0.04 Product Prod/Std Ratio before after ho ho Cyclobunol 0.00 0.189 Ketone 6.78 5.56 Act 1.12 [K] reacted 0.00720 [Cyclobutanol] 0 . 002 0.04 K Tetradecane 0.00477 313 Decyl alcohol 0.00430 Column Conditions #5 Dodecyl mercaptan 0.04 M Quencher Prod/Std Conc (M) Ratio 0.00 0.278 Act 0.437 [__Benzaldehydél 0. 00209 0.04 K Octadecane 0.00397 313 Type II product 0.00493 Column Conditions #6 Prod/Std Ratio before after ho ho 0.339 0.288 8% conversion 210 N-METHYL-4-METHYL-4-BENZOYLPIPERIDINE(Continued) 0.04 K tetradecane 0.00464 313 Octadecane 0.00408 Column Conditions # 8 Solvent System Prod/Std Ratio(cyc) Prod/Std Ratio (DIS) benzene 0.212 0.5 M pyridine 0.122 10% 1-PrOH 0.217 20% l-PrOH 0.174 30% l-PrOH 0.196 40% 1-PrOH 0.193 unirradiated --- Act 4.19 [K] reacted 0. 0206 0.04 K tetradecane 0.00464 313 decyl alcohol 0.00414 Column Conditions # 7 3.86 5.64 4.92 5.38 5.41 5.36 6.86 0.04 K Octadecane 0.00397 Piperylene quencher 313 (50:50 benzenezl-propanol) Column Conditions # 3 Quencher Prod/Std 4 /¢ Conc (M) Ratio 0 0.516 0.500 1.00 1.04 0.409 1.22 2.08 0.328 1.52 3.13 0.458 1.09 4.01 0.428 1.17 Solvent Prod/Std System Ratio benzene 0.182 0.5 M pyridine 0.00 10% l-PrOH 0.0933 20% 1-PrOH 0.0520 30% 1-PrOH 0.0411 40% 1-PrOH 0.0368 Act 4.19 [Benz aldehyde] 0 . 00 1 0.04 K piperylene sensitizee Column Conditions # 2 313 1 Ratio .555 PipyI trans 4 7.87 0.0714 3.80 3.92 0.0390 3.58 1.96 0.0217 3.26 1.96(Acph) 0.0679 --- Intercept 3.18 ktT for first two points = 0.38 211 N-BENZYL-4-METHYL-4-BENZOYLPIPERIDIEE 0.04 K tetradecane 0.00331 313 decyl alcohol 0.00395 Column Conditions # 5 Dodecyl mercaptan 0.0199 l-methylnaphthalene quencher Quencher Prod/Std 4O Conc (M) Ratio /¢ 0.00 0.686 1.00 0.000822 0.563 1.22 0.00164 0.475 1.44 0.00247 0.408 1.68 0.00329 0.362 1.90 Act 1.125 [Benzaldehydéj 0.0034 ktt=27115 l-METHYLCYCLOHEXYLPHENYL KETONE 0.04 K Octadecane 0.0193 313 Column Conditions # 8 Solvent Prod/Std Prod/Std System Ratio (cyc) Ratio (K) 70% 1-PrOH 0.112 2.65 70% 1-PrOH 0.13 M NMP 0.128 2.65 0.5 M pyr 0.023 2.92 0.4 M pyr 0.1 M NMP 0.042 2.88 0.45 M pyr 0.05 M NMP 0.036 2.88 0.04 K tetradecane 0.00301 313 octadecane 0.00398 column conditions # 8 Solvent Prod/Std System Ratio 0.5 M pyr 0.126 Act 0.983 0.04 K tetradecane 0.00301 octadecane 0.00399 column conditions #8 neat isopropanol N-methylpiperidine quencher 313 Quencher Prod/Std Conc (M) Ratio 0.00 0.740 0.094 0.643 1.87 0.676 2.80 0.698 Act 0.983 [Cyclobutanol] 0 . 00 37 212 l-METHYLCYCLOHEXYLPHENYL KETONE (Continued) 0.04 K tetradecane 0.00301 0.04 K tetradecane 0.00302 313 decyl alcohol 0.00402 313 heptadecane 0.00434 column conditions #7 column conditions # 8 Dodecanethiol 0.0104 Acetonitrile/1% H 0 N-methylpiperidine quencher N-methylpiperidiné quencher diluted 2:5 for analysis Quencher Prod/Std 4o Prod/Std 4 Quencher / Conc (M) Ratio °/¢ Conc (M) Ratio 4 0.00 0.927 1.00 0.00 0.174 1.00 0.156 0.553 1.68 1.00 0.139 1.25 0.312 0.308 3.01 2.00 0.113 1.53 0.468 0.184 5.04 3.00 0.098 1.74 0.625 0.118 7.86 Act 0.987 --- Act 0.983 --- 0.00(noH20)0.181 --- @enzaldehydé] 0. 0056 Act 1.09 --- [Cyclobutanofl 0 . 00083 LI ST OF REFERENCES 9. 10. 11. 12. l3. 14. 15. 16. 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