M—‘-~.q~v~.— M' ABSTRACT A KINETIC STUDY OF THE QUENCHING 0F TRIPLET BUTYROPHENONE BY MONOOLEFINS: T 1? A MODEL FOR KETONE TRIPLET-MONOOLEFIN INTERACTIONS f by Irene Emily Kochevar I“ l! i This research was undertaken to determine the nature of the interaction between ketone triplets and ground state monoolefins in solution which leads to quenching of the ketone triplet. Norrish Type II photoelimination which occurs from the triplet state of butyrophenone was partially quenched by various amounts of monoolefins. The rate constants for quenching, kq, were determined using Stern-Volmer kinetics. The values of kq for the monoolefins were determined relative to that for 2,5-dimethyl-2,4-hexadiene. The diene was assumed to quench with the maximum rate constant in benzene solution. The quenching efficiencies of the chloroolefins increased with the number of chlorosubstituents on the double bond. §j§;l,2- dichloroethylene quenched triplet butyrophenone ~30 times less efficiently than the diene whereas tetrachloroethylene was only ~3 times less efficient than the diene. Product formation was not detected between trichloro- or tetrachloroethylene and butyrophenone. These VESUTts along with others in the literature indicate that energy transfer is responsible for the quenching of ketone triplets by chloroolefins. Values of kq were determined for a series of eleven acyclic alkenes. Alkyl substitution on the double bond generally increased k . For q 7 l —1 example, kq for gi§72—pentene was 5.07 x lO M" sec but increased 7 M“ sec" for 2,3-dimethyl-2-butene. The Q; isomer of to 46. x lO a EIETEEED§.°]efi" pair was always a 2-3 times better quencher than the trans isomer. Less than 15 percent of the quenching resulted in product formation between the ketone and olefin in the two cases studied. Quenching by the cyclic olefins was more efficient than quenching by most of the acyclic gj§;l,2-disubstituted ethylenes. The values for kq decreased in the order C8 > C7 3,C4 > C5 > C6 > norbornene. About 45 percent of the quenching by cyclohexene yielded product which was postulated to result from allylic hydrogen abstraction. Olefin dimers resulted from the quenching of butyrophenone by cyclopentene and norbornene. These results were most consistent with predominant quenching by the hydrocarbon olefins through formation of a complex in which the olefin acted as an electron donor and the ketone as an electron acceptor. Radical addition of the carbonyl oxygen to the olefin was eliminated as a quenching mechanism because the kq values were too large for this process and the relative rates expected for addition to cyclic olefins were almost opposite to those observed. Quenching by energy transfer to the olefins was ruled out except for the small cyclic olefins which probably have lower triplet energies than their acyclic analogues. A general scheme for triplet ketone—olefin interactions is proposed. The scheme points out how the mechanism and rate constant for interaction depend upon the relative triplet energies of the ketone-olefin pair and upon the electron donor and acceptor ability of the olefin and triplet ketone , respectively. A KINETIC STUDY OF THE QUENCHING OF TRIPLET BUTYROPHENONE BY MONOOLEFINS: A MODEL FOR KETONE TRIPLET-MONOGLEFIN INTERACTIONS by ,_ ‘ ;_‘A Irene Emily Kochevar A THESIS Submitted to Michigan State University in partial fulfillnent of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry “rem ACKNOWLEDGMENTS The writer gratefully acknowledges Professor Peter J. Wagner for his good-humored patience and direction. His imaginative approach to chemistry has had a profound influence on the shape and sense of this work. The writer also thanks her friends and colleagues in the _ \ chemistry department for creating a pleasant atmosphere for research and study. For financial support from the Dow Chemical Company during the summer of l967 and from the Lubrizoil Foundation for the last year, the writer is very grateful. A work of this nature is never without its trying moments. The writer especially thanks her husband for his willingness to assume a fair share of abuse during these periods. III. TABLE OF CONTENTS Acknowledgement INTRODUCTION ...................... A. Triplet Energy of Ethylene and Substituted Ethylenes ..................... B. Quenching of Hg and Cd Triplets .......... C. Quenching of Benzene and Substituted Benzene Triplets ...................... D. Quenching of Dialkyl Ketone Triplets ........ E. Quenching of Phenyl Alkyl Ketones and Diphenyl Ketones ...................... RESULTS . . . . . . . . ................ A. Quenching of Butyrophenone Triplets by Olefins. . . B. Quenching Which Results in Product Formation Involving Butyrophenone .............. C. Quenching of prrifluoromethylbutyrophenone Triplets ...................... D. Sensitized Dimerization of Norbornene and Cyclopentene .................... DISCUSSION ....................... Chloroolefins ................... 33> . Acyclic olefins .................. Cyclic olefins ................... Summary ...................... Further Experiments ..... . .......... ‘n (11 c n . . Model for Ketone Triplet-Monoclefin Interactions. . Page 22 29 29 36 37 38 39 41 42 47 51 51 53 IV. VI. TABLE OF CONTENTS (Continued) Page EXPERIMENTAL ...................... 56 Chemicals ...................... . 56 Buterphenone .................. 56 Valeraphenone .............. . . . . 58 Monoolefins ...... . ............ 60 Irradiation .- ..................... 62 Methods . . .‘. . . . ................. 62 Quenching experiments .............. 62 Quantum yield determinations ........... 65 Ketone disappearance studies ........... 65 Olefin dimerization studies ........... 7l Phosphorescence Spectrum of prTrifluoromethyl- butyrophenone . . . . . . . . . . . . ......... 72 REFERENCES. . . . . . ................. 73 APPENDIX. . ...................... 78 ii LIST OF FIGURES FIGURE Page 1 Energy level diagram for ethylene showing twisting vibrational levels ........... 3 2 Energy level diagram for ethylene showing C-C stretching vibrational levels. ....... 3 3 Jablonski Diagram for Butyrophenone ....... 30 4 Quenching of Butyrophenone Triplet by Monoclefins. . . . . . . . ........... 50 5 Scheme for Ketone Triplet-Monoclefin Interaction. . ................. 54 iii -N Kalli" . I TABLE II III IV VI VII VIII IX XI XII XIII XIV XV XVI XVII LIST OF TABLES Page Singlet-triplet Absorption Spectra of Substituted Ethylenes. . . .............. 5 Quenching of (3P])Hg and (3P])Cd by Olefins ...... 6 Quenching of Triplet Benzene by Olefins ........ 9 Sensitized Photolysis of l-Methylcyclohexene ..... ll Quenching of Triplet Acetone by Olefins ........ 13 Product Quantum Yields From Ben20phenone and Benzaldehyde with Olefins ............... 23 Isotope Effects on the Quenching of Benzophenone Triplets ....................... 25 Quenching of Phenyl Alkyl and Diphenyl Ketones by Nonconjugated Olefins. . . . . . ........... 28 Lifetime of Buterphenone. . . . . . ......... 32 Quenching of Triplet Butyrophenone by Hydrocarbon \Olefins ........................ 33 Quenching of Triplet Butyrophenone by Chloroolefins. . 34 Quenching of Triplet Buterphenone by Olefins ..... 35 Chemical Quenching of Butyrophenone Triplet ...... 36 Quenching of Butyrophenone and 97Trifluoromethyl- butyrophene by Monoolefins . . . Quenching of Triplets by Alkyl Substituted Ethylenes . 43 Quenching of some Carbonyl Compounds by Alkyl Substituted Ethylenes. . . . . ........... Sums of Quantum Yields for Sensitized Olefin Reactions. ...................... 47 iv Fl if ! E L_y TABLE XVIII XIX XX XXI XXII XXIII XXIV XXV XXVI XXVII XXVIII XXIX XXX XXXI XXXIa XXXII XXXIII LIST OF TABLES (Continued) Page Quantum Yield of Butyrophenone ......... . . . 57 Purification of Butyrophenone . . ........ . . 58 Solutions in a Typical Run ...... . . . . . . . . 64 Samples for Tetrachloroethylene/butyrophenone Product Study . . . . . . .............. 67 Samples for Trichloroethylene/butyrophenone Product Study . ..... . . . . . . ........ 67 Samples for cis-4- Methyl- -2- -pentene/butyrophenone Product Study .......... . ....... 68 Samples for 2- -Methyl- -2- -butene/butyrophenone Product Study . . . . . . . . . . . . . . . . . . . . 68 Samples for Cyclohexene/butyrophenone,Product Study . 68 Product Formation from Quenching of Butyrophenone by Tetrachloroethylene. . . ...... . . . . . . 69 Product Formation from Quenching of Butyrophenone by Trichloroethylene. . . . . . . ...... . . . . 69 Product Formation from Quenching of Butyrophenone by §j§;4-Methyl-24pentene ........ . . . . . . 70 Product Formation from Quenching of Butyrophenone by 2-Methyl-2-butene ..... . . .......... 70 Product Formation from Quenching of Butyrophenone by Cyclohexene. . . . . . . . . . . . . . . . . . . 70 Sensitized Dimerization of Cyclopentene ..... . . 7l Sensitized Dimerization of Norbornene . . . . . . . . 7l Quenching of Triplet Butyrophenone by 2, 5- -Dimethyl- -2 4- hexadiene . . . . . . . . . . . 79 Quenching of Triplet Butyrophenone by 2, 5- -Dimethyl -2, 4- hexadiene . . . . ........ - 79 FIFE-x- .9. TABLE XXXIV XX V XXXVI XXXVII XXXVIII XXXIX XL XLI XLII XLIII XLIV XLV XLVI XLVII XLVIII LIST OF TABLES (Continued) Page Quenching of Triplet Butyrophenone by 2,5-Dimethyl-2,4-hexadiene ........... 79 Quenching of Triplet Butyrophenone by 2,5-Dimethyl-2,4-hexadiene ........... 80 Quenching of Triplet Butyrophenone by 2,5-Dimethyl-2,4-hexadiene ........... 8O Quenching of Triplet Butyrophenone by 2,5-Dimethyl-2,4-hexadiene ........... 80 Quenching of piTrifluoromethylbutyrophenone by 2,5-Dimethy -2,4-hexadiene ......... 8l Quenching of piTrifluoromethylbutyrophenone by 2,5-Dimethy -2,4-hexadiene ......... 8l Quenching of Triplet Butyrophenone by Tetrachloroethylene ...... . ........ 8l Quenching of Triplet Butyrophenone by Tetrachloroethylene ............... 82 Quenching of Triplet Butyrophenone by Trichloroethylene ................ 82 Quenching of Triplet Butyrophenone by Trichloroethylene ................ 82 Quenching of Triplet Butyrophenone by sis; and trans-l,2-Dichloroethylene ....... 33 Quenching of Triplet Butyrophenone by trans-l,2-Oichloroethylene ........... 83 Quenching of Triplet Butyrophenone by trans-l,2-Dichloroethylene ........... 84 Quenching of Triplet Butyrophenone by §1§:l,2-Dichloroethylene ............ 84 Quenching of Triplet Butyrophenone by £1§:1,2-Dichloroethylene ............ 84 vi TABLE XLIX LI LII LIII LIV LV LVI LVII LVIII LIX LX LXI LXII LXIII .. ’. LIST OF TABLES (Continued) Quenching of Triplet Butyrophenone trans- l ,2 Dichloroethylene. . . . . Quenching of Triplet Butyrophenone trans-l,2-Dichloroethylene. . . . . Quenching of Triplet Butyrophenone 2, 3- Dimethyl- -2- butene . . . . . . Quenching of Triplet Butyrophenone 2,3-Dimethyl-2-butene . . ..... Quenching of Triplet Butyrophenone 2, 3- Dimethyl- -2- butene . . . . . Quenching of Triplet Butyrophenone 2,3-Dimethyl-2-butene . . ..... Quenching of Triplet Butyrophenone 2-Methyl- -L butene . . . . . . . . Quenching of Triplet Butyrophenone 2-Methyl-2-butene . . . . . . . . . . Quenching of Triplet Butyrophenone 2- Methyl -L butene . . . . . . . . Quenching of Triplet Butyrophenone gjsyB-Hexene . . . . . . . . . . . Quenching of Triplet Butyrophenone gig: and trans-3-Hexene . . . . . . Quenching of Triplet Butyrophenone trans-4-octene . . . . . . . . . . Quenching of Triplet Butyrophenone cis-4- Methyl -L ~pentene . ..... Quenching of Triplet Butyrophenone trans-4-Methyl-2-pentene ..... Quenching of Triplet Butyrophenone trans-4-Methyl-2-pentene . . . . . vii by Page 87 87 87 88 89 89 89 9O TABLE LXIV LXV LXVI LXVII LXVIII LXIX LXX LXXI LXXII LXXIII LXXIV LXXV LXXVI LXXVII LXXVIII LIST OF TABLES (Continued) Quenching of Triplet Butyrophenone cis- 2- Pentene . . . . . . . . Quenching of Triplet Butyrophenone by gis: and trans-Z-Pentene . . . . . Quenching of Triplet Butyrophenone by gig: and trans-Z-Pentene . . . . Quenching of Triplet Butyrophenone by gig; and trans-Z-Pentene . . . . . Quenching of Triplet Butyrophenone trans-2,3,5,5-Tetramethyl-3-hexene. . . . Quenching of Triplet Butyrophenone by Z-Methyl-l-butene . . . . . . . Quenching of Triplet Butyrophenone by 2-Methyl-l-butene Quenching of Triplet Butyrophenone by l-Pentene . . . . . . . . . . . Quenching of Triplet Butyrophenone Bicyclo[4. 2. 0]oct- 7-ene . . . . . Quenching of Triplet Butyrophenone Bicyclo[4. 2. 0]oct- 7-ene . . . . . Quenching of Triplet Butyrophenone Norbornene. . . . . . . . . . . . . Quenching of Triplet Butyrophenone Norbornene. . Quenching of Triplet Butyrophenone Cyclopentene. . . . . . . . . . . . . Quenching of Triplet Butyrophenone Cyclopentene. Quenching of Triplet Butyrophenone Cyclohexene . . . viii O o o I e o o e e I o I Page by. . . 90 . . . 90 ..... e e 9] e e e 9] by , 92 . . 92 . . . . 92 o . e o e e e 93 .L’. . . 93 I.” ...... 93 '3’ ...... 94 L” ...... 94 by. ..... 95 by , 95 5”. . . 9s TABLE LXXIX LXXX LXXXI LXXXII LXXXIII LXXXIV LXXXV LXXXVI LXXXVII LIST OF TABLES (Continued) Page Quenching of Triplet Butyrophenone by Cyclohexene ................... 96 Quenching of Triplet Butyrophenone by Cyclohexene ................... 96 Quenching of Triplet Butyrophenone by Cyclohexene ................... 96 Quenching of Triplet Butyrophenone by Cycloheptene ................... 97 Quenching of Triplet Butyrophenone by Cyclooctene ................... 97 Quenching of Triplet Butyrophenone by l,4-Cyclohexadiene ................ 97 Quenching of prTrifluoromethylbutyrophenone by 515:2-pentene ................. 98 Quenching of prrifluoromethylbutyrophenone by 2—Methyl-2-butene ............... 98 Quenching of p:Trifluoromethylbutyrophenone by Norbornene .................. 98 I. INTRODUCTION The research reported in this dissertation lies within the general area concerning the interaction between atoms or molecules in their first excited triplet states and ground state nonconjugated olefins. .p-w—‘fl—fi This interaction quenches the triplet state molecule or atom and may result in a variety of products. When quenching yields triplet state Fu_,.nhm olefin, the process is called triplet-triplet energy transfer (Equation l). The triplet state olefin may subsequently isomerize, dimerize or undergo a variety of other inter- and intramolecular reactions (Equation 2). 35* and 150 represent sensitizer molecules in their excited triplet k 35* + lolefino ——et——-> 1so + 3olefin* (l) 3olefin* -———-——{E> Products (2) state and ground state, respectively. The olefin triplet and ground state are shown as aolefin* and lolefino. In other cases, chemical quenching occurs. The predominant chemical quenching reactions are allylic hydrogen abstraction (Equation 3) and addition to the olefin double bond (Equation 5). Both pathways can lead to products involving the sensitizer (Equations 4 and 6). k . 35* + nzcnc=cn2 —"——> ~SH + RZCCR=CR2 (3) .5” __——-———{;> Products (4) k 35* + R2C=CR2 ———a—9 Rzlc—cn2 (5) S. R2?——CR2 ———————{3> Products (6) S. The relative triplet state energies of the triplet state molecule or atom (sensitizer) and of the olefin (quencher) are a major factor in determining the type of quenching and the rate constant for quenching. Consequently. research pertaining to the triplet state energy of ethylene is reviewed first. Quenching of various types of sensitizers is then discussed in order of decreasing sensitizer triplet energy (metal atoms, benzene and substituted benzenes, dialkyl ketones, phenyl alkyl ketones and diphenyl ketones). A. Triplet Energy of Ethylene and Substituted Ethylenes The zeroth vibrational level of the first excited triplet state of ethylene is predicted“2 to have a 90° angle between the planes of the -CH2 groups whereas the lowest vibrational level of the ground state is planar. Walsh3 predicted that rehybridization of the -CH2 groups from sp2 to sp3 stabilizes the perpendicular triplet. His prediction has been subjected to calculations‘NS’6 but the results have been inconclusive. The energy levels of ethylene can be best discussed in terms of the following diagrams. 0 ‘io mo 17“ '5“ Angle between planes of -CH2 groups Figure 1. Energy level diagram for ethylene showing twisting vibrational levels Relative C-C distance Figure 2. Energy level diagram for ethylene showing C-C stretching vibrational levels In Figure l the vibrational levels drawn represent the quantization of the twisting vibration about the carbon-carbon bond whereas in Figure 2 the quantization of the carbon-carbon stretching vibration is shown. The actual vibrational levels result mainly from combinations of these two vibrational modes. Examples of Franck-Condon allowed (vertical) S + T transitions are represented by solid arrows and nonvertical . ——r‘r—‘ ._ -m,’ transitions by broken arrows. Although the singlet-triplet absorption spectrum of ethylene has 5. been published798 and numerous triplet energy calculations have been .4- reported“:9 there is still disagreement among researchers over the energies of these transitions. Reid7 in 1955 and Evans8 in 1960 reported the singlet-triplet spectrum of ethylene. The absorption maximum was observed at 2700 A (106 fig?%) and the longest wavelength absorption occurred at 3484 X (82 %§%%). These researchers concluded that the nonvertical transition from the zeroth vibrational level of ground state ethylene to the zeroth vibrational level of twisted triplet ethylene required about 82 %%%%3 This value for the 0-0 transition has been accepted by many researchers. Calculations by Baird9, Lodquet“ and others predict energies of 54-70 %%%%for the lowest vibrational level of twisted triplet ethylene. Merer and Mulliken1° in a review article concluded that the lowest triplet level of ethylene may be as low as 60£§%%.based mainly on the ability of low energy sensitizers to isomerize olefins. The singlet-triplet absorption spectra for five alkyl substituted ethylenes have been determined by Itoh and Mullikenll. The results are given in Table I. TABLE I. Singlet-triplet Absorption Spectra of Substituted Ethvlenes. __'— OIEfi" Aonset’ cm’] Eonset’%§T% Amax’ cm’1 Emax’ggTE propene 28,200 80.5 33,900 97.0 2-methylpropene 28,200 80.5 33,000 94.5 transfz-butene 28,200 80.5 32,800 93.8 trimethylethylene 27,000 77. 29,850 85.5 tetramethylethylene 26,400 75.5 29,400 84.l The 02-induced singlet-triplet spectra of gi§_and trgn§;l,2-dichloro- ethylene reported by Grabowski and Bylina12 appear to begin at 3850 A and 4000 A respectively. If the onset of singlet-triplet absorption results from nonvertical transition to a twisted molecule, the energy of the 0-0 transition can be estimated to "Eonset' Dimerization of cyclic olefins sensitized by molecules with known triplet energies can be used to estimate olefinic triplet energies also. Sensitized dimerization is thought to involve triplet-triplet energy transfer and subsequent attack of triplet olefin upon a ground state olefin molecule to yield dimer13. Arnold)“ has reported the ratios of dimer/oxetane obtained from the quenching by norbornene of a series of phenyl alkyl ketones with triplet energies in the range 71-75 %%%%a Oxetane results from chemical quenching. Dimer was virtually the only product when the ketone had a > n 1ca 1ng at e trip et 0 nor ornene cou e pro uce ET RESP—m t th th 1 f b ldb d d with an energy as low as 72 55%1-. Because norbornene' s bicyclic structure does not allow it to twist significantly, a near-planar triplet must have .fi_-nh._'.a.; A l been formed. Taking into account the facts that low efficiency energy transfer does occur when a donors triplet energy is 2-3 %§%%-less than that of the acceptor15 and that some twisting can occur, the planar triplet may be estimated to have an energy of 80-85 kcal/mole. This estimate of the planar triplet energy can also be used to . F'B explain the acetone (ET = 80 $§§éJ5) photosensitized dimerizations of : cyclopentene17, cyclobutenela, l-methylcyclobutene18 and norbornene19. These dimerization studies indicate that the Eonset values measure a the energy of the vertical transition to the lowest vibrational level 3 l..« of the planar olefin triplet. B. Quenching offlg_and Cd Triplets Atomic mercury has a lowest triplet energy of l13 gggézo. A review covering mercury photosensitization20 lists the relative quenching efficiencies of a number of unsaturated hydrocarbons. Examination of a sample of the values reported (Table II) does not reveal a relationship between olefin structure and quenching efficiency. TABLE II. Quenching of (3P])Hg and (3P1)Cd by Olefins. 3 Olefin Hg(3P]) Cd( P1) ethylene 0.90 1.03 2 .09 ethylene-d -—— .96 2 .0l propene ' 0.93 l.l8 t .04 l-butene -—- 1.08 t .09 l-pentene l.00 -— iso-butene .95 1.33 t .03 cis-Z-butene l.00 1.02 t 07 cyclohexene -- 1.02 : .10 trimethylethylene -;g .99 t .1] tetramethylethylene :93 1.13 t .04 l,3-butadiene Tsunashima and Sato21 studied the pressure dependence of the Hg- photosensitized gi§:trgn§_isomerization of 2-butene and concluded that a transient complex was formed between Hg(3P1) and the olefin (Equation 7). This complex (HgC* or HgT*) broke up to give ground state Hg and either triplet olefin (8*) (Equations 8, 9) which isomerized (Equation 11) or vibrationally excited ground state olefin (CJr or TI) which did not isomerize (Equations 10, 12). 3119* + C(or T) —> 1190 (or HgT*) (7) ch* (or HgT*) % Hg + 3* (8) HgC* (or HgT*) + M --———-§> Hg + 8* + M (9) H90 (or HgT*) —> Hg + ci (or if) (10) 3* ——> me + l/2T (n) ci (or T?) —> c (or T) (12) Other mercury photosensitized reactions include decomposition of ethylene22 and cycloalkene523, and dimerization of ethylenez“. Internal cycloaddition of nonconJugated dienes photosensitized by mercury has been studied by Srinivasan25 (Equations 13, 14). © 253; R 3 [fl (‘3) C _H_9253; a 22$ + [I] (14) Atomic cadmium (ET = 87.7 kcal) has been used to photosensitize the decomposition of ethylene26 with low efficiency and the interconversion of £1§:, trans: and gem:ethylene-d5532 Huziker26 assumed that transfer of energy from triplet Cd must have been to a twisted ethylene. Consequently, he postulated the initial formation of a complex between 30d1 and the olefin. The relative efficiencies of olefins in quenching triplet cadmium atoms was studied using competitive quenching by Tsunashima, Satoh and Satoza. Their results, summarized in Table II, are similar to those found for triplet mercury photosensitization ’Q121(~. -gfl. -,.. suggesting that energy transfer is exothermic to both metal atoms. C. Quenching of Benzene and Substituted Benzene Triplets kcal 9 - The triplet energy of benzene (84.4 EST32 ) is greater than the E of ethylene and substituted ethylenes. Consequently, triplet onset olefins have been proposed as intermediates in all benzene photosensitized reactions. The scrambling of deuteriums3°a31, gj§;tran§_isomerization31, and (at low pressures) decomposition to hydrogen and acetylene3° of 1,2-dideuteroethylene hawabeen photosensitized by benzene, although the rate constants for these processes were lower than those obtained with Hg-photosensitization39 Hirokami and Sato studied the pressure dependence of the first two of these reactions when photosensitized by a number of benzene derivatives31. Schmidt and Lee used competitive quenching of the benzene photo- sensitized isomerization of gl§:2-butene to determine the kinetic isotope effect on quenching by ethylene32. The observed isotope effect, kH(C2H4)/kD(CZD4) a 1.7 t .2, was attributed to the higher triplet energy of the deuterated compound as determined from the relative onsets of the singlet-triplet absorption Spectra of the two olefins. Since quenching of benzene by butadiene and butadiene-d6 did not exhibit an isotope effect, kH(C4H6)/kD(C406) = 1.0 3 .2, the authors concluded that quenching of benzene by ethylene was an endothernnc process. The benzene photosensitized gj§;t:gg§_isomerization of 2-butene in the gas phase was reported by two groups in 19633393“. Cundall, Milne and Fletcher observed that the isomerization occurred with a variety "“ ‘ “ “‘ “C of other sensitizers as long as their triplet energies were greater than 65 %%%%-and concluded that the 0-0 transition of 2-butene required an energy of about 65 %§%%3“. Lee, Denschlag, and Haninger used the benzene ..:._ .— .__‘. .1 | photosensitized 51§3trans-isomerization of Z-butene to moniter the relative quenching efficiences of other olefins35. Their results are summarized along with those of Morikawa and Cvetanovic35, who made a similar study, in Table III. The ratio of initial rates, Rc+t/Rt+c’ of 2-butene isomerization was determined to be 1.03 t .0235. TABLE III. Quenching of Triplet Benzene by Olefins. relative uenchin rate constants Olefin fee, Denschlag + Baninger NoriRawa + Cvetanovic 230 O m 6° 30 70° ethylene 0.17 0.22 0.25 0.33 propene 0.52 0.4 9—— -—— l-butene 0.46 0.50 0.51 -—— l-pentene 0.47 0.54 ——- -— isobutene -— 1.27 -- -—— 2-methyl-l-butene ——- 0.80 ——- —— glsfz-butene 1.00 1.00 1.00 1.00 trans-Z-butene 1.09 ——- -— -—— cyc I opentene 0 . 85 — — — trimethylethylene 1.65 1.61 ——- —— tetramethylethylene 3.00 2.67 2.75 2.29 1,3-butadiene 11.8 16.2 15.8 13.0 The contrast between these results and those found for metal atom photosensitizations suggests that the quenching process is now endothermic. Both groups of researchers pointed out that the relative quenching efficiencies of the olefins paralleled the order found for the addition of electrophilic reagents to olefins. In addition, Morikawa and Cvetanovic suggested that energy transfer from triplet state benzene to 3 olefin occurred through the formation of a complex. During the lifetime of the complex, the olefin assumed a twisted conformation and accepted i energy from the benzene triplet. From the observation that the relative quenching efficiencies differed less at higher temperatures, these E _ authors concluded that an activation energy for energy transfer was indicated. Benzene has also been used to photosensitize olefin reactions in the liquid phase. Kropp37‘“° and Marshall"1 have reported the products of benzene and substituted benzene photosensitized reactions of some cyclic monoolefins. l-Methylcycloalkenes photosensitized by benzene or a substituted benzene in the absence of hydroxylic compounds isomerized to the exocyclic isomer and dimerized (Equation 15). CH3 . A/ h» (CHQ/ll W (012)“+1 + (CHZn) mt] (CNN) (15) The yield of exocyclic isomer increases in the order norbornene < n = 3 < n = 4 < n = 533. Some reduction of the double bond was found when "ethyl substituted benzenes were used to photosensitize the reaction (Equation 16). f r.)- 911 tic (in! 11 CH /_\/ 3 CH3 (6%” h“ \ (012),,+1 <16) sens.“7 The ratio of dimer to exocyclic alkene produced from the sensitized photolysis of l-methylcyclohexene was determined“° (Table IV). TABLE IV. Sensitized Photolysis of 1-Methy1cyclohexene. Sensitizer ET' kcal/mole methylegegizlohexane Benzene 34a 10' Toluene 33b 7'2 p-Xylene BI'SZC 1'8 Mesitylene 30c 0'5 aRef. 29; ”o. F. Evans, J. Chem. Soc. , 2753 (1959); C0. R. Kearns, J. Chem. Phys. , 36,1608 (1962). Photosensitized photolysis of cycloalkenes and l-methylcycloalkenes in xylene-methanol solution yields mixtures of dimers, exocyclic alkenes, methanol addition products (Equation 17) and various products attributed to radical reactions. OCH3 CH3 hv \ (CH/)T\)l + CH30H x lane )7, (CH2)n+1 (17) 2c, y In general, the products from the photosensitized reactions of cyclo- alkenes indicate that the excited state of cyclopentenes and 2-norbornenes exhibited radical behavior whereas those formed from cyclohexenes and cycloheptenes undergo protonation. The radical behavior of the smaller ring compounds was attributed to the n,n* triplet. The authors concluded that protonation of the six- and seven-membered rings probably occurs through the formation of a trans-double bond but the possibility of protonating the triplet was not discounted (Equation 18)“°. gjsfolefin §E%%—-E> 3olefin* --———{E> trans-olefin + H+ (18) carbonium ' ion Intramolecular addition of alcohol has been photosensitized by toluene39 ) (Equation 19). L 2 ho toluene E (19) H OH CH2-O 2 Intramolecular quenching of benzene triplets was reported for dilute solutions of gi§:1-phenyl-2-butene by Morrison“2:“3. Kinetic experiments in which the sensitized isomerization of the double bond 1 for was quenched by piperylene yielded a value of 2.0 x 108 sec" intramolecular triplet-triplet energy transfer“3. Nakagawa and Siga1““ also studied the kinetics of this sensitized §1§:tran§_isomerization but concluded that four processes were occurring: singlet-singlet inter- and intramolecular energy transfer and triplet-triplet inter- and intramolecular energy transfer. 13 D. uenchin of Dialk l Ketone Tri lets Quenching of the triplet state of dialkyl ketones has been studied in both the gaseous and liquid phases. Research to determine the mechanism of quenching in the liquid phase, triplet-triplet energy transfer or chemical quenching, has been reported whereas triplet-triplet energy transfer has been assumed to account for quenching in the gas phase. . .., c.‘.-. 'ul -, The first report of ketone photosensitized isomerization of a monoolefin was made by Hammond, Turro and Leermakers“5. These researchers observed that in solution 2-pentene and 1,2-dichloroethylene isomerized L when irradiated with wavelengths which they did not absorb in the presence of a variety of ketones from acetone (ET = 80 %§%%) to fluorenone (ET = kcal 53 ms" Rebbert and Ausloos carried out a systematic study in the gas phase of the relative quenching of acetone phosphorescence by a series of alkyl substituted monoolefins“5. Their results in Table V should be compared with those in Tables II and III for metal atoms and benzene. TABLE V. Quenching of Triplet Acetone by Olefins Relative u . Relative a Olefin Quenching x 10 Olef1n Quenching x 10 ethylene 0.053 1,4-pentadiene 0.38 propene 0.11 2-pentene 0.42 l-butene 0.11 2-methyl-l-butene 0.48 l-pentene 0.13 trimethylethylene 0.64 isobutene 0.22 l-methylcyclohexene 0.67 cyclohexene 0.30 tetramethylethylene 2.90 trans-Z-butene 0.31 l,3-butadiene 290 cis-Z-butene 0.33 1,3-pentadiene 440 styrene 10,000 The order of increasing quenching efficiencies parallels both that expected for decreasing triplet energies of the monoolefins and for increasing ease of attack by electrophilic ketone triplet. Consequently, no conclusion can be drawn regarding the mechanism of quenching from these data alone. In addition, these researchers reported that tetra- methylethylene quenched acetone-d6 phosphorescence 1.14 times more efficiently than acetone-h6 phosphorescence and postulated that the longer lifetime of acetone-d6 was responsible for this effect. But Schmidt and Lee32 showed that when the difference in lifetimes of acetone-h6 and a . mum-“A. ..._.4.) ..v .. acetone-d6 (r = .20 and .51 msec, respectively) are taken into account 9 the isotope effect was kH (CH3COCH3)/kD (CD3COCD3) = 2.2. The isotope effect for the quenching of acetone phosphorescence by ethylene and deuterated ethylene, k(CzH4)/k(C204), was determined to be 1.9 t .232 compared to the value of 1.7 found for quenching of benzene triplet. For quenching by propylene and propylene-d6 the isotope effect was somewhat smaller32. The mechanism of acetone photosensitized gi§;tran§_isomerization of 2-pentene has been studied in solution by Kearns16 and by Saltiel“7. Kearns calculated from the initial rate of isomerization of gig-2- pentene a rate constant for quenching of triplet acetone by 915-2- pentene of about 2 x 107 11'1 sec-1 at 25°C. The quenching rate constant at -78°C was about twenty times smaller. Because the rate constant for quenching was approximately 100 times smaller than the expected diffusion-controlled value and decreased as the temperature decreased, Kearns postulated that triplet-triplet energy transfer between acetone and gig-Z-pentene required an activation energy. The following mechanism was postulated to account for these results (Equations 20, 21, 22). whe stab fore 22) . opera at 301 lechal predon low ta 5 from 51 of Z-pe (Equati with $81 339 :5: 15 3A* + lco __JEL_;> [3A* --- 1Co] (20) [3A* ___ 1CD] __EB_€;> 3A* + 1Co (21) [3A* __- ICO] __LE_;> 1A0 + 3c* (22) where A represents acetone and 1Co represents gj§;2—pentene. Because F ' the collision complex, [3A* --- 1Co], was assumed to have negligible : stability, ka and kb would have the same temperature dependence. There- fore, the observed temperature dependence was attributed to kc (Equation f 22). In addition, the authors suggest that two mechanisms may be operating because the photostationary gig/tran§_ratio increases from 1.7 at 300°K to 2.5 at 200°K but decreases to 1.1 at 77°K. The two competing mechanisms suggested are a thermally activated interaction which predominates around room temperature but which gives way partially at low temperatures to a quantum-tunneling process. Saltiel also concluded that two quenching mechanisms were operating from studies of the acetone and acetophenone photosensitized isomerization of 2-pentene“7. He reasoned that if only one mechanism were operating (Equations 23-27), the ratio, a/l-a, for a given quencher would not change with sensitizer. so i> 15* ., 35* (23) k 35* ___JL2;> so (24) k 35* + to ____£L€;. *x (25) "6 E 35 + co *X (26) iso con val: kcal with lhe ‘ birac olefi 16 *X -——Z——E> etc + (T-a)Co (27) where 5 represents sensitizer, co and to are E and trans ground state 2-pentene and X* represents an unspecified comnon intermediate. Equations 28 and 29 were derived assuming steady state r. approximations for 35* and X*. { K 1: 1 = 1 4 t ¢t+c 1__a (1 + Tn—S t ) (28) L 1— : J— (‘| + k4 ) (29) i °c+t “ IE6h] 4~ The ratio of the intercepts obtained from plotting the inverse isomerization quantum yields, -—l- and -J—- , versus the initial ¢t-vc °c+t concentration of 1/t_r_a_ni- and 1/_ci_s-2-pentene, respectively, yield values for 1%; . The values obtained for acetone and acetophenone (ET=74 kcal/mle)photosensitization (1.17 and 1.90, respectively) were compared with that obtained from benzene photosensitized i somerization of Lbutene (1.00), which was assumed to occur by triplet-triplet energy transfer. The increase in 1%: from unity was attributed to intervention of a biradical intermediate for-ed from attack of the ketone triplet on the olefin (Equation 30) which decayed to fly and trans-Lpentene 3 e CH3 0 o ' H + 2 5 Csz «GE 3 17 Equation 31). The decay ratio, 1%. from the biradical was eXpected CH3 ‘ C2H5 0 O 0 (if e or R—{. e ____> R/lk (3") ' 2"5 R' CH3 R' CH T a \:::\ + (I-a) CHC._/CZH5 C2H5 to differ from that found for olefin triplet decay. The authors concluded that acetone photosensitized isomerization proceeded predominantly via formation of olefin triplets whereas in acetophenone sensitization the biradical pathway, chemical quenching, is largely responsible far the isomerization. Many irradiations of dialkyl ketones in the presence of mono- olefins have been reported in which some or all of the products were characterized but kinetic measurements were not made. In many of these cases, the product mixture can be accounted for by a single quenching mechanism or a combination of competing mechanisms. But in some cases, no choice between mechanisms can be made on the basis of products alone. Some examples of the former situation are acetone photosensitized dimerizations, oxetane formation, and some reductions. Combinations of these reactions were often found. Acetone photosensitized dimerization of nonconjugated olefins occurs when the carbon-carbon double bond is in a four or five-membered ring or a strained polycyclic compound. The mechanism, which requires triplet-triplet energy _. flu -—-v=r.a-v “1 2 1 ‘ .. 18 transfer, is given in Equations 32-35 (11 = 2, 3, 4). /\ k . 35* + (CH\2)n/l| _fllé 15° + “@I /"‘\ . /’"‘\ /’T‘\ z"\ earl/H) A A /\ /‘\ (CHQn/‘jflfln —9 (C%D&H2)n A A A (CH2)n l—l (0)2)" % 2 (CH2)nH \~_a’ "‘~*/ \~_// (32) (33) (34) (35) Acetone photosensitized dimerizations are often accompanied by reductions (see below). For example: [11* i—“—>Q3+D/T (36) Ref. 18 (38) Refs. 19, and 48 OX8 ketone triplets is believed to take place through closing of the Light-initiated oxetane formation which results in quenching of biradical formed from the attack of a ketone triplet upon a ground state olefin (Equations 39-91). 3 0—1 231 -—> Le This mechanism has been invoked to explain the formation of L L .1 * / oxetane in the following reactions. (”71 % (ii (39) (40) (41) (42) Ref. 49 (43) Ref. 50 (44) Ref. 51 (45) Ref. 52 ‘4 1,1...“ I-——- I ‘t—m no MT" ~- A.‘ . z , - a...” 20 Schroeter and Orlando53 have studied the addition of acetone triplets to vinyl ethers and found that the major product always resulted from attack on the olefin to give the more stable biradical (Equation 46). 3 0% OR /u\ + RCH=CHOR fi 4' + 401 0 5 0R . . R (46) R OR 1:1. 1:1. (73318;) (33333;) The authors noted that since the major product was not the exclusive product, as would have been predicted by relative rates of free radical attack5“, other factors such as cleavage/coupling ratios are important in determining product ratios. Interesting results were found when the quenching of hexadeutero- acetone by tetramethylethylene was studied by Japar, Pomeratz and Abrahamsonss. The products from photolysis to 1% conversion with either 31303 or 3657A light in solution consisted partly of non- deuterated acetone and hexadeuterotetramethylethylene (Equation 47). The authors proposed that a vibrationally excited oxetane was formed which then decomposed. CD3” Frog 1 to dec (Produl (Produc E(llllltio “MHZ; 21 3 CH CH [— b CH3 ‘1 7 * \J 3 9 318's 0 /‘—\ —'_> a- “age." .A A CH3 CH3 CD3 ; 9H3 c113 co3 __ C03 CH3_1 / J: W) /ji\ + CH CH3 0 CH co3 >=< + CD3 co3 CH3 CH3 CH3 H3 c113j ico3 Reductions which are initiated by triplet ketones occur by combinations of hydrogen abstraction and radical coupling reactions. R- in the following equations may be the ketone triplet, the olefin triplet or other radical generated by these triplets. k R- + H __Ls RH + (48) 2R- ——9 LR From the identity of the reduction products it is usually possible to decide if quenching of the ketone triplet occurred by energy transfer (products from triplet olefin are found) or by chemical quenching (products from hydrogen abstraction by acetone triplets are found). Equation 50 shows a case where photoreduction predominated over dimerization and oxetane fbrmation55. upon M Cl ted disser Preseni Ph oxen”, 22 i + O we)“. 699+ 99 Examples of photosensitized reactions for which a choice between quenching mechanisms cannot be made are found with some gi§;trans isomerizations. Morrison has studied the intramolecular photosensitized isomerization of 2-hexen-4-ones and 2-hepten-5-ones“2. ’JL\/A§§/, ._l¥%___;>. sz\/<§j (51) )K o + 0 M jig-9 W /| (52) Either energy transfer or initial attack of the carbonyl oxygen upon the olefin can explain the isomerization reaction. E. Quenching of Phenyl Alkyl Ketones and Diphenyl Ketones The kinetic results reviewed below along with those of Saltiel cited above were published after the research presented in this dissertation was begun. The relationship of these results to the present research will be covered in the Discussion. Photosensitized olefin dimerization, gisftrgg§_isomerization, and oxetane formation have been reported to result from the interaction of HE 1|!.1| MINI... V Benzi Benz: Benza Benza Benza Benzol Banzai 0) 0f conj ”"8 p11 A 1‘“ 9' 23 Olefins with phenyl alkyl ketone triplets whereas quenching of diphenyl ketone triplets has been reported to yield only the latter two processes. Because of their low triplet energies (ET = 75-68 %§%%) quenching of these ketones by triplet-triplet energy transfer is not expected to be efficient although the results of Saltiel“7 and Arnoldl“ discussed above indicate that at least for acetophenone (ET = 74.5 kcal/mole) some energy transfer quenching does occur. The quenching rate constantShawebeen determined for several triplet ketone olefin pairs. The first research in this area was published by Yang who studied the quenching of benzophenone and benzaldehyde triplets by 3-methyl-2-pentene57 and by 2,3-dimethyl-2-butene53. The quantum yields obtained for oxetane formation and gi§;t§gg§:isomeri2ation (for 3-methy1-2-pentene) are given in Table VI. TABLE VI. Product Quantum Yields From Benzophenone and Benzaldehyde with Olefins. Sensitizer ET Olefin (conc.) on ¢c+t °t+c Benzaldehyde 71.5 2,3-dimethyl-2-butene 1M 0.465 Benzaldehyde 71.5 2,3-dimethy1-2-butene 4M 0.527 Benzaldehyde 71.5. 2,3-dimethyl-2-butene neat) 0.397 Benzaldehyde 71.5 cis-3-methyl-2-pentene (1M) 0.45 Benzaldehyde 71.5 tFins-3-methyl-2-pentene (1M) 0.45 Benzophenone 68.0 cis-S-methyl-Z-pentene (1M) 0.16 Benzophenone 68.0 trans-3-methy1-2-pentene (1M) 0.16 e e “—0 Imloolll o e N—l e|~|||| Oxetane formation and isomerization were quenched by varying amounts of conjugated diene at constant olefin concentration and the results were plotted according to the Stern-Volmer equation (Equation 53): for Suc may that form K11 by 1.2-d ”15 resu 24 ¢° kq [diene] = l + - (53) ¢ kd +7k+ [olef1n]_ where ¢° = quantum yield for isomerization or oxetane formation in absence of added diene, a = quantum yield with added diene, kq = rate constant for quenching of carbonyl triplet by diene (assumed to be diffusion controlled), kd = rate constant for decay of carbonyl triplet in absence of olefin and diene, and kr = rate constant for quenching interaction of olefin and carbonyl triplet. When kd is assumed to be small relative to kr [olefin], the values summarized in Table VIII are obtained. Yang found that photosensitized isomerization of and oxetane formation from 3-methy1-2-pentene were quenched at the same rate. Such results indicate that a common excited state of the sensitizer may be responsible for both reactions. In addition, he concluded that isomerization of the olefin resulted from an olefin triplet formed upon cleavage of the initially formed biradical (Equation 54). F. '— i I .4 k O—- Ab . + 1olefino _a_> R-'( 4- ——>oxetanes . ,| I R' | \=o + 3[olefin]* / RI Kinetic isotope effects on the quenching of benzophenone triplets by 1,2-dichloroethylene and 2-butene have been studied by Caldwe1159’50. His results are summarized in Table VII. L _ \L (54) ‘l' .— 111.1%) 1 25 TABLE VII. Isotope Effects on the Quenching of Benzophenone Triplets. (1:33:23 Olefin Pair kH/kD Ref. c->t c_ig_-CHC1=CHCl/ci_s-CDCl=CDCl 1.15 2 .02 59 1+1: m-cncncucvm-cnwcnm 1.18 2 .02 59 c+t c_ii-CH3CH=CHCH3/§_ii-CH3CD=CDCH3 1.02 . .01 59 c->t gg-CH3CH=CHCH3/Qs-CH3009-CHCH3 0.935 . .02 59 c->t £i_s_-CH3CH=CHC2H5/_ci_s_—CH3CD=CHCZH5 1.00 2 .01 50 t-vc M-cu3cn=cnc2R5/m-cn3cn=cnc2H5 1.01 . .01 50 oxetane _ci_s-CH3CH=CHCH3/ci_s-CH3CD=CDCH3 1.03 5 .02 50 Caldwell pointed out that if biradical formation was the rate- determining step in quenching as was previously postulated for benzo- phenone an inverse isotope effect should have been found since the spZ-hybridized carbons in the olefin would change to sp3. The authors proposed that formation of a complex between the ketone triplet and the olefin before formation of a biradical would be consistent with the observed isotope effect (Equations 55-58). k 15:) + >=< —9——> [x] (55) Ph h 0 [x] ——-—> P») i (55) Ph benz bUtEI Pmba tCEtol; of 15 °" Exam O-——[: 0 Ph-j) . . _______5, Ph/H\P; (cis and trans) >===< (57) Ph 4 . —> <59 Caldwell also determined the rate constants for quenching by gig; 2-butene of a series of substituted benzophenones. Because the results (Table VIII) indicate that quenching increases as electron attracting groups are introduced onto the carbonyl compound, an electron-transfer complex was proposed as the intermediate, X50. + _ \. / [:ArzC-—O +C——C+ :] / ‘\ Also consistent with this intermediate was the observation that benzophenone triplet was quenched six times more rapidly by §i§:2- butene than by 515:1,2-dichloroethylene even though the latter olefin probably has a lower triplet energy59. Quenching by a nonconjugated diene, 1,4-cyclohexadiene, of the acetophenone and e-chloropropiophenone photosensitized isomerization of gigfpiperylene was reported by Braun, Hammond and Cassidysl. Based on examples of possible singlet electronic-vibrational energy transfer, 27 these authors proposed an analogous process for triplet quenching (Equation 59, Table VIII). TXI ’ ___>. ’0 1 (59) + i R + [::J o’JL\R. [::j The present research consists mainly of a systematic study of the effect of changing olefin structure on the rate constant for quenching triplet state butyrophenone, a phenyl alkyl ketone. Butyro- phenone undergoes Norrish Type II photoelimination exclusively from its triplet state yielding acetophenone and ethylene (Equation 60). O .. I = 5 The quenching rate constants were determined by measuring the quantum yield of acetophenone without olefin and with various concentrations of olefin present and applying the Stern-Volmer relationship. 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RESULTS A. Quenching of Butyrophenone Triplets by Olefins The triplet state of butyrophenone was obtained by irradiating benzene solutions of the ketone through Pyrex and a filter solution which allowed wavelengths 3000 to 3200 A to pass. The excited singlet state initially obtained, S], intersystem crosses with unit quantum efficiency62 to the first excited triplet state, T]. In the absence of quencher molecules, triplet butyrophenone abstracts a hydrogen from the methyl group to form a biradical, 153 (Equation 61). 3 OH -CH k U3 ___, x42 <60 CH c5“5' 6 5 I ‘Radiative and unimolecular radiationless decay of triplet butyro- phenone to the ground state are both much slower than the hydrogen abstraction process and can be ignoredG“. The hydrogen abstraction process, therefore, occurs with unit efficiency unless a quencher is present. The biradicals formed by hydrogen abstraction undergo disproportionation, cleavage and coupling in proportion to the rate constants for these processes: kdis’ kc] and kc , respectively. p DiSproportionation yields ground state ketone (Equation 62), whereas cleavage and coupling yield new products, acetophenone enol and a 29 ”rm .7 0 0H -CH “dis c H ' 5 5 OH OH ~cu kc1 CH/LJ 2 fl c5H5 \ + CHZBCHZ (63) 5 5 011 , k fiat Sc” CBHSAti (54) c5”5 cyclobutanol, respectively, (Equations 63, 64). The processes from light absorption to product formation can be sunnarized in the following diagram. $13 _m__> 5.4 Figure 3. Jablonski Diagram for Butyrophenone. The quantum yield for production of acetophenone, 03, in the absence of added quenchers can be expressed as: 31 0 a °A iisc ion“ (55) where ¢isc = quantum yield for intersystem crossing IBR = quantum yield for biradical formation 8 g kc1/(kcl + kcp + kdis)' The quantum yield for intersystem crossing is unity for buterphenoneGZ. The quantum yield for biradical formation, 43R, equals kr/(kr + k4 [Q']) where the primed variables refer to quencher not intentionally added to $.—“—‘—*—T-. ‘r—TT’ To! the solutions. In the presence of added triplet quencher, Q, the following expression is appropriate for the quantum yield of acetophenone production (Equation 66). k r ¢ . ¢ . + I l + . B (66) A isc kr k q[Q ] kq [Q] Dividing Equation 65 by Equation 66 yields the Stern-Volmer expression (Equation 67). 4 k [0] “TL ‘ ‘ * —lE‘—+qk_"[0"']_ (57) A r q The lifetime of the butyrophenone triplet in the absence of added quencher, r, is equal to l/(kr + k4 [Q']). Therefore, the Stern-Volmer relationship can be written as: - l + qu [Q] (68) 32 In order to determine 1, 2,5-dimethyl-2,4-hexadiene was choosen as a quencher since this diene appeared to quench triplet butyrophenone at the maximum rate in benzene solution, kq = 5 x 109 M'] sec'171. Because the value of kq was known, the slopes of plots of °A/°A versus [0] were used to calculate x. The values found for r for the four samples of butyrophenone used in these studies are summarized in Table IX. TABLE IX. Lifetime of Butyrophenone. Sample I x 107, sec I l.l4 II 0.99 III 0.80 IV 1.13 A series of non-conjugated olefins were used to quench the triplet state reaction of butyrophenone. Plots of °Al°A versus [olefin] were drawn for each olefin and the slopes of these plots were determined. Tables X and XI list the olefins used as quenchers, the slopes of the Stern-Volmer plots and the sample of butyrophenone used. Cyl 541 1 ,1 33 TABLE X. Quenching of Triplet Butyrophenone by Hydrocarbon Olefins. Olefin Slope, M'1 Ketone Sample 2,3-Dimethy1-2-butene 52.5 I " 33.7 III " 38.6 III " 37.4 III 2-Methy1-2-butene 14.7 I “ 13.1 III " 13.5 III 513:3—Hexene 3.8 II “ 3.76 IV trans-B-Hexene 1.25 IV cls-I-Methyl-Z-pentene .85 I tFEns-4-Methyl-2-pentene .44 I ” .465 II 533:2-Pentene 3.30 III " 4.06 III " 4.78 III " 5.75 IV trans-Z-Pentene 1.50 III " 1.74 III " 1.83 IV Z-Methyl-l-butene 3.45 I " 2.90 I 1-Pentene .90 I trans-2,2,5,5-Tetramethyl- - exene 1.90 III Bicyclo[452.0]oct-7-ene 3.3 i Norbornene 3.84 III " 3.05 III Cyclopentene 6.02 I “ 5.93 I Cyclohexene 3.05 I “ 4.4 II " 3.85 II “ 4.48 III Cycloheptene 8.6 I Cyclooctene 9.4 I 1,4-Cyclohexadiene 11.6 III TABLE XI. Quenching of Triplet Butyrophenone by Chloroolefins. l Olefin Slope, M' Ketone Sample Tetrachloroethylene 165 I ." 165 I Trichloroethylene 88 II " 76 a II cis-1,2-dichloroethy1ene 18.5 I _ " 38.1: I “ 18.4a IV trans-l,Z-dichloroethylene 48 I — " 43.3: IV " 46 I aIntercept not equal to unity. The actual quenching rate constants for the non-conjugated olefins were calculated from the values of the slopes given in Tables X and XI and the ketone lifetimes given in Table IX. A summary of the quenching constants for nonconjugated olefins along with the relative quenching efficiencies, based on gigfz-pentene = l, are given in Table XII. l.‘:d_o‘4 .4.— n‘vt;m~o_ “"1 1 a“? 35 TABLE XII. Quenching of Triplet Butyrophenone by Olefins. Olefin kq x 10-7’ "-1 sec'] quenchiggazi‘ficiency 2,5-Dimethyl-2,4-hexadiene 500 98.5 2,3-Dimethy1-2-butene 46. t 3. 9.08 2-Methyl-2-butene 14.3 i 1.5 2.82 gjgf3-Hexene 3.58 t: .25 .71 Eggg§:3-Hexene 1.11 .22 glge4-Methyl-2-pentene .745 .15 Eggggf4-Methyl-2-pentene .414 t .030 .08 glgfz-pentene 5.07 21.00 1.00 Itggg§:2-pentene 1.89 t .30 .37 Z-Methyl-l-butene 2.76 t .25 .54 l-Pentene .79 .16 transgiéfiés,S-Tetramethyl- 2.39 .47 Bicyclo[4.2.0]oct-7-ene 7.5 t .25 1.48 Norbornene 3.70 t .10 .73 Cyclopentene 5.24 t .04 1.03 Cyclohexene 4.2 91.5 .83 Cycloheptene 7.55 1.49 Cyclooctene 8.25 1 1.63 l,4-Cyclohexadiene 14.6 2.88 Tetrachloroethylene 145 :90. 28.6 Trichloroethylene 71.8 t 5. 14.1 _c_1_s_-1 ,LDichloroethylenea 15.2 5 .1 3.20 Eggggfl,2-Dichloroethylenea 40. t 2. 7.90 aIntercept not equal to unity. Error represents mean deviation from average value for two or more runs. Error on single runs estimated to be t 5%. aura—.as—q _. ru-Eum-'¢a.a_1-— -0. ‘1' I i 36 B. uenchin Which Results in Product Formation Involvigg Butyrophenone. A series of irradiations were carried out with several olefins in order to get a minimum value for the fraction of quenching which occurred by a chemical quenching mechanism. The fraction of quenching due to chemical quenching was calculated by dividing the moles of butyrophenone which disappeared during the irradiation but could not be accounted for by acetophenone and cyclobutanol formation by the moles of butyrophenone triplets quenched. The data for these calculations are in the Experimental Section and the results are summarized in Table XIII. TABLE XIII. Chemical Quenching of Butyrophenone Triplet Olefin Minimum Percent of Chemical Quenching Tetrachloroethylene 2 Tri chl oroethylene cis-4-Methyl-2-pentene 12 2-Methy1-2-butene 5 Cyclohexene 44 These values represent the minimum percent of chemical quenching because chemical quenching which does not consume butyrophenone, i.e., that which involves revertible biradical formation,is not included. The fact that appreciable acetophenone was formed during the irradiations did not appear to affect the results. I l i 9‘ . 37 2’ \ o I F v r l ,. e 4 C. Quenching of gyTrif1uoromethylbutyrophenone Triplets. In order to obtain further indications of the type of quenching interaction taking place between phenyl alkyl ketones and nonconjugated olefins, the quenching of pftrif1uoromethylbuterphenone was studied. The carbonyl group of the triplet state of this compound should be more electron deficient than that of butyrophenone. Its triplet energy was determined to 72 kcal/mole, 2.5 kcal/mole lower than that of butyrophenone. The triplet state lifetime of petrifluoromethyl- 7 buterphenone was determined to be .6 x 10' sec by quenching with 2,5-dimethyl-2,4-hexadiene. Therefore, the p:trifluoromethyl substituent increases the reactivity of the carbonyl oxygen toward y-hydrogen abstraction by a factor of about 2. Rate constants for quenching of p:trifluoromethylbuterphenone and butyrophenone by three monoolefins are compared in Table XIV. TABLE XIV. Quenching of Butyr0phenone and p:Trif1uoromethylbutyrophenone by Monoolefins. Olefin Butyrophenone pflrifluoromethylbutyrophenone kq x 10'7, M'1 sec-1 kq x 10'7, M'l sec.1 913:2-Pentene 5.07 t 1 10.6 Z-Methyl-Z-butene 14.3 t 2 25. Norbornene 3.70 t .l 4 .68 38 D. Sensitized Dimerization of Norbornene and C clo entene As predicted by the results of Arnold's study of the dependence of sensitized dimerization on ketone triplet energyl“, butyrophenone sensitized the dimerization of norbornene as well as that of cyclo- pentene. According to the mechanism for sensitized dimerization (Equations 32-35), the olefin concentration influences the dimer yield I ‘1 in two separate steps. Higher olefin concentration should increase . the efficiency of the energy transfer process (Equation 32) and the attack of triplet olefin upon ground state olefin (Equation 33) at the ‘W‘—":“"‘=' L expense of the competetive processes not involving a ground state olefin molecule. An 1.13-fold increase in the gxg7tggg§:gxg_dimer yield was found as the norbornene concentration was increased from 0.999 to 2.812 M and a 2.3-fold increase in dimer yield was found as the cyclopentene concentration changed from 0.156 to 0.782 M. g7Trifluorobutyrophenone sensitized the dimerization of norbornene about 20 times less efficiently than butyrophenone at the same olefin concentration. Since the efficiency of Equation 33 should remain the same, the efficiency of the energy transfer process appears to have decreased by a factor of 20. The shorter lifetime of p:trif1uoromethyl- butyrophenone alone only accounts for half of the decreased efficiency. Consequently, it appears that other quenching processes are able to compete more effectively with energy transfer from p:trifluoromethy1- butyrophenone than from butyrophenone. III. DISCUSSION The decrease in Type II photoelimination quantum yield from butyro- phenone in the presence of monoolefins is attributed to quenching of the ketone triplet by the monoolefins. The possibility of singlet-singlet energy transfer can be eliminated since the singlet energies of the monoolefins are > 50 kcal/mole greater than the singlet energy of butyrophenone. Chemical quenching of the ketone singlet can also be i l i i 1 1 :A 1 l eliminated because of the ketones short singlet lifetime. The commonly proposed mechanisms for quenching of ketone triplets by nonconjugated olefins are triplet-triplet energy transfer and radical addition of the carbonyl oxygen to the carbon-carbon double bond. Triplet-triplet energy transfer only occurs with a rate constant approaching the diffusion rate constant in solution under certain conditions. The triplet energy of the donor must be equal to or greater than that of the acceptor. Lower rates of energy transfer have been observed when this condition is not met15955. Also, the triplet state lifetime must be long enough to allow for a number of collisions to take place because energy transfer does not appear to take place on every collision55157. "et 35* + 1olefino :> 150 + 3olefin* (1) 39 'I 1' 9'5 :gv nmm 40 3olefin* ———————§> a giseolefin + (l-a)trans-olefin (69) 3olefin* + lolefin0 ———-—j§> olefin dimer (70) When the acceptor is an olefin, it has been shown that energy transfer causes both isomerization and dimerization. Radical attack by the oxygen of the triplet ketone upon the carbon- carbon double bond yields a biradical which either cleaves or couples. Allylic hydrogen abstraction, another means of chemical quenching, has not been an important interaction except in one case discussed below. H R 3 * ka 0 I: :J + RCH=CHR —9 (7‘) c H c5’15 " R 5 5 R H C H 6 5 R R kl I Cl 5 i + cis-olefin C6H5 R + (l-a)trans-olefin R kl CGHS-I-vl R €Cp (72) R H Comparison of triplet state benzophenone with t-butoxy radical has shown that nn* ketone triplets act as electrophilic radicalsea. Consequently, the rate of radical addition should increase as the ketone triplet becomes more electrophilic and as the olefin becomes more nucle0philic. {___-u 1.3.; .r 1’15e44 -. 4: q 1 41 A. Chloroolefins. The chloroolefins were the most efficient of quenchers of the monoolefins studied. The rate constants for quenching increased as chlorines were substituted for hydrogens on ethylene. Tetrachloro- ethylene quenched triplet butyrophenone with a rate constant only m3 times less than the maximum rate in benzene solution and gi§;l,2- dichloroethylene was about 10 times less efficient than tetrachloro- ethylene. Chloro substituents should decrease the rate of electrophilic addition to the double bond59. Consequently, the trend in k predicted for quenching by radical addition is opposite to that observgd. The lack of oxetane formation between buterphenone and tri- or tetrachloroethylene or between ben20phenone and the dichloroethylene559 also argues against quenching by radical addition since the biradical formed would be expected to couple part of the time. If the triplet energies decrease as the number of chlorines on the double bond increases as has been found for the singlet energies70, ket should increase in the order dichloro- < trichloro- < tetrachloro- ethylene. The vertical triplet energies of the chloroolefins12 may be approximately equal to ET for buterphenone. The magnitude of the k 's is consistent with slightly endothermic energy transferls. q Since the trend predicted for k with respect to chloro substituents q by an energy transfer mechanism is observed and the magnitude of the rate constants is consistent with inefficient energy transfer, triplet- triplet energy transfer is pr0posed as the mechanism of quenching by the chloroolefins. QHL;§F(."... l'nth-LHJ-i - - _ lifllg‘allljb 8:21 I. 1.4.11.4} 2-15 it 42 This conclusion is consistent with Caldwell's results which indicate that triplet ben20phenone (ET = 69 kcal/mole) transfers energy to sis; and trans-l,2-dichloroethy1ene59. The rate constant reported for 7 1 quenching of benzophenone by trans-l,2-dichloroethy1ene was 1.3 x 10 M'1 sec-1 whereas kq for quenching of butyrophenOne was 40. x 107 M' sec']. Caldwell based his conclusion nainly on the fact that he found a normal isotope effect on quenching (kq(ClHC=CHC1)/kq(ClDC=CHCl) > 1). An inverse isotope effect is expected for quenching by radical addition to the double bond. 111'---=—-5-.~ -r-- ~ -- ~41 B. Acyclic olefins. The rate constants for quenching by eleven acyclic olefinsll varied from being ~10 to ~1000 times less than that of the diene. In general, kq increased with the number of alkyl substituents on the double bond and the gj§_isomer of a gi§:trgg§_olefin pair was always a 2-3 times better quencher than the trgg§_isomer. The vertical triplet energies of these olefins are greater than ET for butyrophenone. As seen from the following rough calculation, endothermic energy transfer would occur with lower rates constants that those determined. The decrease in energy transfer efficiency as a function of the triplet energy of the quencher is given by Equation 73, assuming that AET represents an activation energy for energy transfer. A log ket 1 = - —— (73) AET 2.303111 43 If the vertical triplet energy of gisgz-pentene is about 80 kcal/mole (calculated by subtracting l kcal/mole for each alkyl substituent from the value of 82 kcal/Hole for ethylene), energy transfer from butyrophenone is about 5.5 kcal/mole endothermic. Since exothermic energy transfer in benzene proceeds with a rate constant71 equal to 5 x 109 M'] sec'], ket for 913:2-pentene should be less than 1 x 10 -l -l M sec . Since the measured k is over an order of magnitude 1 4 q 1 l 6 greater than this value, endothermic vertical energy transfer does not appear to responsible for the quenching by monoolefins. In addition, a comparison of the relative quenching rates for four representative olefins with benzene, acetone and butyrophenone (Table XV) shows that the range between the least and the most efficient varies only by a factor of 10 from benzene to butyrophenone. If energy transfer quenching alone was determining these rate constants the variation should be much greater because quenching by energy transfer of butyrophenone is about 9 kcal/mole more endothermic than quenching of benzene. TABLE XV. Quenching of Triplets by Alkyl Substituted Ethylenes. R R Sensitizer ET, kcal/mole :Z/R R\-:::/ ;f::/B Benzene 84.4a .54 1.00 1.6 2.7 Acetone 80b .32 1.00 1.5 7.0 Butyrophenone 74.7C .16 1.00 2.8 9.1 aRef. 29; R. F. Borkman and D. R. Kearns, J. Chem. Phys., 44, 945 (1966); ‘0. N. Pitts, Jr., 0. R. Burley, J. c. Mani and A. 0. Broadbent, J. Am. Chem. Soc., 99, 5902 (1968). 44 Energy transfer to a twisted olefin (non-vertical energy transfer) has been proposed to account for endothermic energy transfer to conjugated olefinsss. This pr0posa1 was based on the observation that the rate constants for quenching of a series of sensitizers did not decrease as rapidly as Equation 73 predicted as the sensitizer triplet energy decreased. Two factors indicate that non-vertical energy transfer is not occurring to the nonconjugated olefins in this study. First of all, the rate constants for non-vertical energy transfer to gjgfolefins are always less than those for the trggg_isomer whereas the Opposite result was consistently found in the present study. Secondly, the kq values for cyclic olefins are larger than kq for gj§;2-pentene. If twisting was involved in the quenching process, restraining the double bond in a ring should decrease kq. The observed rate constants are also larger than expected for quenching by initial radical addition. Other electrophilic radicals, such as t-butoxy, abstract allylic hydrogens from olefins more rapidly than they add to them72. Since the rate constant for abstraction is 5 1 -1 less than 10 M' sec , k is expected to be even lower. In addition, a the lack of isotope effect reported by Caldwelle° for the quenching of ben20phenone by 2-butene cannot be reconciled with a radical addition mechanism which would predict an inverse isotope effect on kq. In total, the results obtained from studies of the quenching of ketones by acyclic olefins appear to rule out both energy transfer and initial radical addition as the predominant quenching process for triplet butyrophenone. 4S Quenching by formation of a complex which has charge-transfer character appears to be consistent with all of the kinetic results. This complex could lead to the biradical from which the observed products are formed or to ground state molecules (Equations 74-77). RIR * H —k-C—> E: ji‘ (74) $31.11. —“> I) 4 R kd ljl\ + >Fzz (12+ > < I QR (77) If the olefin is the donor and the ketone the acceptor, the rate constant for this process, kc’ should increase as the olefin becomes electron rich and as the ketone becomes electron deficient. Increasing the number of (electron-donating) alkyl substituents on the double bond, was found to increase kq as predicted. Data from the present research combined with Yang's and Caldwell's results (Table XVI) further support quenching by charge-transfer complex formation. 14-1.11...’ “fllyr lawn—5.41.. -fi 46 TABLE XVI. Quenching of Some Carbonyl Compounds with Alkyl Substituted Olefins. k x 107 MI] sec:I Ketone g b b ET,kca1/mole CR2=CR2 CRR' =CHR fi-CHLCHR' Butyrophenone 74.7 46c 14.3c 5.07c p-Trifluoromethyl- c c . butyrophenone 72. -—- 25 10.6 F “1 Benzaldehyde 71.5 100d 83e -—- V Benzophenone 58.5 130d 20e 8f A“: *4 gang“. aR = methyl; bR = methyl, R' = methyl or ethyl; cPresent work; ref. 55; eref. 55; fref. 58. 41-“ .A. .- a The ketones are listed in the order in which their triplet states increase in electrophilicity. The order which kq increases is seen to be roughly the same. Consequently, formation of a complex of the form 0- .1)... I: could be responsible for the quenching. The rate of formation of this complex should be sensitive to the electron accepting ability of the ketone rather than its ET. Similar results obtained by Caldwell for substituted benzophenones58 were pointed out in the Introduction. Caldwell also proposed quenching by complex formation to explain his results. The possibility that the complex collapses to ground state molecules in addition to yielding a biradical, can be tested for by summing the quantum yields of isomerization and oxetane formation when the ketone is completely quenched. 47 If the sum is unity this energy wasting step (Equation 76) is not important. Pertinent data are presented in Table XVII. TABLE XVII. Sums of Quantum Yields for Sensitized Olefin Reactions. Sensitizer Olefin ¢c+t ¢t+c ¢ox i-K ¢Total Benzaldehydea 3-Methyl-2-pentene .18 .12 .45 .50 .75-.90 Benzophenonea 3-Methyl-2-pentene .36 .24 .16 .20 .76-.80 AcetOphenoneb Z-Pentene .50 .26 c ——- .76 aRef. 52:5Ref. 46; cOxetane formation was not reported. The sum is not unity in the cases studied indicating that an energy wasting step does occur. This result is additional evidence against either an energy transfer or a radical addition mechanism since neither of these mechanisms can account for total quantum yields less than unity. The rate constants for quenching are not unreasonable if the quenching is occuring by complex formation since this process does not involve bond formation. C. Cyclic olefins The cyclic olefins quench triplet buterphenone with rate constants ~2 orders of magnitude lower than the maximum rate constant in benzene solution. The quenching rate constants for the cyclic olefins were larger than for most of the cis-l,2-dia1kylsubstituted acyclic olefins. Radical addition can be discarded as a probable quenching mechanism based on two factors. First of all, the order of radical addition is predicted73 to be C4 > 06 > C5 > C7 > C8 whereas almost the opposite T-t'n. -4--)‘-~—. .‘o—g-u‘... eAsn— ._. .. " . a . order was found for kq. Secondly, as for the acyclic olefins, the rate constants were too large for radical addition to a carbon-carbon double bond. Also, Arnold found that benzophenone triplet abstracted hydrogens from rather than adding to cyclohexene7“. The relative rates of ka to kh should be the same for butyrophenone triplet. Chemical quenching did appear to account for a large fraction (0.44) of the quenching by cyclohexene (Table XIII). The large number of products appearing in the vpc traces of photolyzed samples containing cyclohexene and the lability of its allylic hydrogens75 indicated that quenching by allylic hydrogen abstraction was occurring with cyclo- hexene. The vpc traces from other cyclic olefins did not indicate significant photoreduction. Although the kq values for the cyclic olefins appear to be too large for vertical energy transfer, sensitized dimerization of cyclo- pentene and norbornene is observed. This conflict may be resolved by proposing that energy transfer and complex formation are competing quenching processes for the cyclic olefins. The seven and eight membered rings should have the same triplet energies as the gi§:1,2-dialkyl- substituted olefins. Consequently, energy transfer is slow and most of the quenching is occurring by complex formation. The larger rates for the ring systems must reflect greater ability to form a complex with charge-transfer character. The smaller ring cycloalkenes may have lower triplet energies than their acyclic analogues. This effect could be due to rehybridization of the olefinic carbons from sp2 in the ground state to sp3 in the triplet. Such rehybridization would be expected to lower the triplet 49 energy by relieving some of the strain in the molecule. From absorption spectra, the five and six-membered cyclic olefins appear to have lower singlet energies than the Sigrl,2-dia1kylsubstituted olefins75. The observed kq values for the small cycloalkenes therefore are a combination of kc and ket' A rough estimate of the fraction of energy transfer occurring with norbornene can be made. The data in Table XIV show that kq doubled for £1572-pentene when the ketone changed from butyrophenone to (g:trifluoromethylbutyrophenone but only increased by a factor of 1.25 ‘—__—._-F__.-_ .1..-_—._.__h.-‘4__..z._; 4.9 ‘4' i 1 for norbornene. Assuming that quenching of p:trifluoromethylbutyro- phenone by cis-Z-pentene is almost entirely by complex formation and that energy transfer to norbornene decreases by an order of magnitude because of the 2.5 kcal/mole decrease in the sensitizer triplet energy, the fraction of quenching of buterphenone by energy transfer comes out to be 0.35. Therefore, complex formation is still the predominant quenching mechanism. The following scheme summarizes the conclusions from the above discussion. Figure 4. \V C H 6 5 BR 3k. H V + CH =CH + ”mfi F5H5 3olefin* Quenching of Butyrophenone Triplet by Monoolefins. 51 0- Shflnnary In summary, the mechanism and rate constant for quenching butyro- phenone triplet depend upon the olefin triplet energy and upon the electron density of the double bond. The chloroolefins, which have triplet energies near that of butyrophenone but do not have electron rich double bonds, quench triplet butyrophenone by energy transfer. f Both the acyclic and the cyclic hydrocarbon olefins quench by formation L of a complex in which the ketone acts as an electron acceptor and the olefin as a donor. The quenching rate constant increases as the olefin Ix. ”Uh-flux..- _ I-w)~e A becomes a better donor. The smaller ring cycloalkenes also quench partially by energy transfer due to their lower triplet energies. E. Further Experiments Some experiments which either test parts of the proposed scheme or are designed to yield further data about the steps in the scheme can now be described. 1. To determine if the values of kq for cycloheptene and cyclo- octene represent only kc’ these olefins should be used to quench gytrifluoromethylbuterphenone. If the high rate constant for quenching of butyrophenone reflects greater complex formation ability of these cyclic olefins exclusively, k should double for g:trifluoromethyl- butyr0phenone as was found f0: gjgyz-pentene and 2-methyl-2-butene. 2. To confirm that quenching of buterphenone by 2-methyl-2- butene and 513:2-pentene is occurring by complex formation, the product(s) detected (see Table XIII) should be identified. If the product is oxetane, the proposed mechanism is confirmed. Since radical addition does not compete effectively against hydrogen abstraction, the oxetane must arise through initial complex formation. 3. To determine the fraction of norbornene quenching due to energy transfer, butyrophenone should be used to sensitize the internal addition of methanol to norbornene triplet (Equation 78). Kropp has proposed that this reaction occurs through the norbornene triplet“°. ‘ 2 ——> (78) HZOH R 20' CH2-———O The moles of adduct formed over the moles of butyrophenone triplets quenched yields the fraction of norbornene quenching which occurs by energy transfer. 4. A study to determine the relative rates of kBR to kd and of k'c1 to k'c and the dependence of these ratios on olefin structure p could be undertaken. The ratio kBR/kd can be determined by measuring the ratio 48R/(4q-43R) where 1BR = °c+t + ¢t+c + 50x and aq = quantum yield of triplets quenched. The ratio k'd/k' can be determined by c measuring the relative quantum yields of isomer:zed olefin and oxetane. The following olefins appear to be appropriate for these measurements: gig:and igggg:3,4-dimethyl-3-heptene; gig: and giggg73-methyl-2-pentene; and, gig: and igggg:3-heptene. The measurements on the trisubstituted olefin will probably be complicated by the formation of two biradicals in unequal amounts. .9" _ f” \_ 53 F. Model for Ketone Triplet-Monoolefin Interaction In view of the systematic kinetic study made in this research and the abundance of both kinetic and product identification data in the literature, it seemed appropriate to propose a model for ketone triplet- monoolefin interactions which was consistent with these data. Such a model would be valuable for its ability to predict quenching rates and E319 products. Also, this model should set up a framework for future research. % The model proposed in Figure 5 is based on competition between two processes, energy transfer and charge-transfer complex formation. The %L5{ relative values of ket and kc determine which process is responsible for quenching. The rate constant for energy transfer approaches the diffusion controlled rate constant when the triplet energy of the ketone is greater than that of the olefin but drops off rapidly as the process becomes endothermic (Equation 73). In the proposed complex the ketone triplet acts as an electron acceptor and the olefin as an electron donor. Consequently, kc increases as electron withdrawing substituents are substituted onto the ketone and as electron donating substituents are substituted onto the olefin. The results obtained in the present study have already been explained in terms of this scheme as it applied to butyrophenone (ET = 74.5 kcal/ mole) specifically. Quenching of acetone (ET = 80 kcal/mole) appears to occur by energy transfer. Acetone-sensitized dimerization of olefins has been found17,13.19. In addition the relative rate constants"6 decrease about as expected for endothermic energy transfer if the olefin vertical triplet energies are calculated by substracting l kcal/mole from the value of 82 kcal/mole for ethylene for each alkyl substituent on the double bond. 54 +R>=( 3KETONE* lKETONEO 1‘ ' R 3 'k R R >0 C< g. .— k 15° R kdim k V BR d R R + 1‘ R \/ “>=-=( . . 4.1“. “H 1KETONEO Figure 5. Scheme for Ketone Triplet-Monoolefin Interaction. 55 Saltiel also reached this conclusion through kinetic studies. Caldwell's results on the quenching of ben20phenone (ET = 69 kcal/ mole) indicate that complex formation is determining the quenching rate constant50. This is reasonable according to the proposed scheme since benzophenone's triplet energy is much lower than that of the olefins and the phenyl groups should make the carbonyl group fairly electron deficient. The results summarized in Table XVI and already discussed are also consistent with this scheme. Some interesting ketone-olefin pairs could be studied to determine the predictive value of this scheme. For instance, an electron deficient olefin such as 1,1,l,4,4,4-hexafluoro-2-butene should be a poor quencher for butyrophenone and worse far g;trifluoromethylbutyrophenone. The value of kc should be low and if the trifluoromethyl groups do not decrease the olefin triplet energy greatly, ket should also be low. The difference between kq for the gig and igggg_isomers of this olefin could be used to determine the mechanism of quenching. The gig_isomer quenches more efficiently than the trans by complex formation and ket for trans is usually greater than that for gig, IV. EXPERIMENTAL Chemicals course of these experiments. Their characteristics can be summarized as follows: Butyrophenone: Four samples of butyrophenone were used in the Sample I: Obtained from Aldrich Chemical Company. Purified by distillation (B.P. = 73°/6 mm Hg) and recrystallization 'Wz‘fl" _T‘e-‘f-‘E from pentane three times at Dry-Ice/isopropanol bath temperature. Initially the slope of a Stern-Volmer quenching plot with 2,5- dimethyl-2,4-hexadiene equalled 568 M'1 (r = 1.14 x 10'7 sec 1 sec'1 for quenching by diene in assuming kq = 5 x 109 11' benzene71). After a four month lapse in the experiments the quenching slope was again deternnned. A value for qu of 465 (1 = .93 x 10'7 sec) was obtained. Sample II: Re-distillation of Sample I yielded butyrophenone which had a lifetime of 0.99 x 10'7 sec as determined by quenching with diene. Sample III: Obtained from Aldrich Chemical Company. Purified by distillation (B.P. = 7l°/6 mm Hg), recrystallization from pentane at Dry-Ice/isopropanol bath temperature two times (first crystals formed and mother liquor discarded), and passed through a 5 cm x 1 cm column of neutral alumina. The quenching 56 57 slopes, 398 and 400 M'l, indicated a value of 0.80 x 10'7 sec for 1 and the quantum yield was determined to be 0.278, and 0.268 (relative to .33 for valerophenond in separate experiments. Sample IV: Obtained from Matheson, Colman and Bell. Purified by distillation only (B.P. = 75°/7 mm Hg). Stern-Volmer quenching plots with 2,5-dimethyl-2,4-hexadiene as quencher yielded lifetimes of 1.05 and 1.13 x 10'7 sec. The higher ,; ' value was taken to be the lifetime of sample IV. Quantum (’1 yield measurements gave values of 0.41 and 0.36 relative to valerophenone. Methods used to determine quantum yields and quenching constants are described in the Methods section of the Experimental. TABLE XVIII. Quantum Yield of Butyrophenone Counts Aceto henone Sample Ketone [CI4H30] CEDEEE‘TEEFSEEEEBE’"[ACEtODhenone] 5A III' Butyrophenone .00252 1.23 .00624 .276 052 1.24 .00626 a Valerophenone .00156 2.39 .00746 .33 III Butyrophenone .00260 .687 .00357 .268 " .00260 .689 .00358 Valerophenone .00156 1.37 .00428 .33a " .00156 1.46 .00455 IV Butyrophenone .00196 1.71 .00671 .41 " .00196 1.72 .00675 a Valerophenone .00196 1.38 .00541 .33 " .00196 1.39 .00545 IV Butyrophenone .00232 .866 .00402 .36 " .00232 .987 .00416 Valerophenone .00295 .504 .00358 .33a " .00296 .650 .00385 aValue determined in ref. 61 ll .1. 58 Simple reduced pressure distillation of butyrophenone appeared to afford the highest purity ketone. A brief study of purification techniques showed that further purification only decreased the quantum yield. The relative yields of acetophenone were determined on samples taken at various stages of the purification procedure and irradiated in benzene solution with equal concentrations of tetradecane present F (Table XIX). 3 at ‘5‘.“- '- la i TABLE XIX. Purification of Butyrophenone I L‘Uh 5' . . . relative Sample Pur1f1cat1on acetophenone yield 3 1 Reduced pressure distillation 1.00 2 From 1, recrystallized 3x from pentane .71 3 From 2, crystals formed in mother liquor 1.00 4 From 2, passed through 1 cm x 6 cm alumina column .57 5 From 3, passed through 1 cm x 3 cm alumina column .76 6 From 4, distilled .58 7 From 5, distilled .66 Valerophenone: The quantum yield measurements for butyrophenone (sample III) were made relative to a sample of valerophenone from Aldrich Chemical Company and purified by A. E. Kemppainen. The slope of a Stern-Volmer plot with 2,5-dimethyl-2,4-hexadiene as quencher was 39 M']. The quantum yield for acetophenone production was assumed to be 0.33 as measured previously53. The quantum yield for butyrophenone, sanple IV, was determined relative to valer0phenone which was obtained 59 from Aldrich Chemical Company and purified by R. Zepp. The quenching constant, k r, was the same as obtained for the previous sample of valerophenoge (Table XVIII). Therefore, the quantum yield was assumed to be 0.33 again. prrifluoromethylbutyrophenone was prepared on 0.075 mole scale from propylmagnesium bromide and pftrifluoromethylbenzonitrile (Columbia f"‘” Chemical Company). The propylmagnesium bromide was prepared by adding from an addition funnel 10.4 g of n-propyl bromide in 20 ml anhydrous ether to 2.06 g of magnesium turnings and 10 ml anhydrous ether at room temperature in a 50 ml 3-necked round bottomed flask equipped g with a condenser and a mechanical stirrer. The nitrile mixed with 10 ml anhydrous ether was added to the Grignard nfixture which had been cooled in an ice-water bath. After stirring overnight the mixture was poured into about 50 ml of 2N HCl and ice mixture. Hydrolysis on a steam bath, separation of layers, extraction of the aqueous layer with ether and reduced pressure distillation yielded 8.3 g (51% yield) of the pure ketone (B.P. = 57°] mm Hg). Tetradecane (Columbia Chemical Company) and thiophen-free benzene (Fischer Chemical Company) were stirred with portions of sulfuric acid until the acid remained clear, washed with sodium hydroxide solution and water and dried with calcium chloride. Tetradecane distilled at 92.5°/4 nnng. Benzene was distilled from phosphorous pentoxide through a 4 foot glass helix packed column. 2,5-Dimethyl-2,4-hexadiene (Aldrich Chemical Company) was recrystallized from melt three times at Dry-Ice/isopropanol bath temperature. 6O Monoolefins: Cyclohexene, cycloheptene, cyclooctene, l,4-cyclo- hexadiene, norbornene and gig: and gggpg:l,2-dichloroethylene were purchased from Aldrich Chemical Company. The following olefins were obtained from Chemical Samples Company: l,4-dichloro-2-butene, gig:3- hexene (96% pure), trans-3-hexene (99% pure), gig:2-pentene (95% pure), iggpg:2-pentene (99% pure), gggpg:2,2,5,5-tetramethyl-3-hexene (99% pure) and cyclopentene (99% pure). Trichloroethylene and tetrachloro- ethylene were Matheson, Coleman and Bell products and 2,3-dimethyl-2- butene was purchased from Columbia Chemical Company. The remainder of ' - the monoolefins, 2-methy1-2-butene, gig: and gggpg:4-methyl-2-pentene, l-pentene and 2-methyl-1-butene were Phillips Petroleum Company Pure Grade. All of these olefins except the chloroolefins and norbornene were purified by preparative gas-liquid phase chromatography. In addition, some were distilled on a spinning band column before chromatographic purification. Initially the olefins were used directly after preparative glpc but in later experiments the olefin purified by glpc was distilled. The olefin purification procedure is noted in the tables which contain the kinetic data for each experiment. The chloroolefins were dried and distilled before use and norbornene was sublimed at room temperature and atmOSpheric pressure. Bicyclo[4.2.0]oct-7-ene was prepared by photoisomerizing gig, gig: 1.3-cyclooctadiene (Aldrich Chemical Company) to the gig, gggpg_isomer and thermally converting this isomer to the bicyclo compound. The procedure described by Liu77 was used. This olefin was also purified by preparative glpc. 61 When storage was necessary, purified olefins were refrigerated. Vapor phase Chromatography Analyses for acetophenone, tetradecane and butyrophenone were performed on Varian Aerograph gas-liquid partition chromatographs. Two models were used: HiFi III Series 1200; and HiFi Model 600C. Ten foot x 1/8" aluminum columns packed with a mixture of 4% QF-l and 1% Carbowax 20M on Chromosorb G at 110-120°C effectively separated the above three compounds. A 20' x 1/8" aluminum column packed with 25% l,2,3-tris(2- cyanoethoxy) pr0pane on 60/80 Chromosorb P in an Aerograph HiFi Model 600-D was used to analyze olefin purity. The recorders used with these chromatographs were equipped with disc intigraters and the signal was produced by flame ionization detectors. Acetophenone concentration was analyzed relative to a known concentration of tetradecane. A 0.2 - 0.6 ul sample of solution containing both acetophenone and tetradecane was injected onto the column and the area under each peak recorded. To correct for the difference in response of the detector to each compound the following equation was used. - _ Counts Aceto henone [acetophenone] - [tetradecane] x C.F. x C6Dfit§‘TEtF3§EEEfiET The correction factor, C.F., was determined to be 2.0 by measuring the number of counts for each compound when mixtures of known concentration in acetophenone and tetradecane were injected. Butyrophenone was analyzed relative to tetradecane in a similar manner. The correction factor was 1.42. 62 Preparative vapor phase chronatography of olefins was carried out with a Hewlett Packard Model 776, Prepmaster Jr. A 20' x 1]?!" aluminum column packed with 25% l,2,3-tris(2-cyanoethoxy) propane on 60/80 Chromasorb P was used. Irradiation All samples in a given run were placed a merry-go-round photolysis apparatus73, which insured equal incident light intensity, and irradiated for the same length of time. A Hanovia 450-watt medium pressure mercury lamp was used as a light source. The region from ..... ___. I .". 3000 A to 3200 A was isolated with a 1 cm path of a filter solution containing 0.002 M potassium chromate in 1% aqueous solution of potassium carbonate. Methods A. Quenching experiments. Two stock solutions were prepared for each run, one containing butyrophenone or p:trifluoromethylbutyrophenone and the internal standard, tetradecane, and the other containing the olefin quencher. Both of the stock solutions were prepared by weighing the appropriate amount of compound into a volumetric flask and diluting to the line with benzene. The concentration and volume of the ketone stock solution prepared for each run depended upon the number of samples to be made from the stock solution. Equal aliquots of the ketone-standard stock solutions were pipetted into 10 m1 volumetric flasks along with varying aliquots of the quencher stock solution. Benzene was added to fill the flasks to volume. The concentrations of ketone and tetradecane were about 0.10 M and 0.0025 M, respectively, in the photolyzed samples. The concentration and volume of the ------ Quencher stock solution also varied depending on the quenching rate constant and the amount of olefin purified. Quenching of two-thirds of the reaction in the sample containing the highest quencher concentration was considered optimal. Conversions were less than 5 percent. A typical run can now be described. Stock solution I: 0.9934 g of butyrophenone and 0.0321 g of tetradecane were weighed into a 25 ml volumetric flask. The flask was filled to volume with purified benzene and inverted several times to mix the contents. [Buterphenone] = 0.268M [Tetradecane] = 0.00625M Stock solution II: 1.1079 g of cyclooctene was weighed into a 25 ml volumetric flask. The flask was filled to the line with benzene and inverted several times. [Cyclooctene] = 0.404M Four m1 aliquots of stock solution I were pipetted into 6 10 m1 volumetric flasks. Aliquots of stock solution II between 1 and 5 ml were pipetted into 5 of the flasks containing stock solution I and all flasks were filled to volume with benzene. The resulting solutions are summarized below. n‘ ...|\._ 64 TABLE XX. Solutions in a Typical Run Sample [Butyrophenone] [Tetradecane] [Cyclooctene] blank 0.107 0.0025 0 1 0.107 0.0025 .0404 2 0.107 0.0025 .0808 3 0.107 0.0025 .1212 4 0.107 0.0025 .1616 5 0.107 0.0025 .2020 Using a 5 ml syringe, 2.8 ml aliquots of these solutions were placed in 13 x 100 mm Pyrex tubes which had been constricted about 1 cm from the mouth of the tube. Two tubes were filled from the "blank" sample and one from each of the samples containing cyclooctene. The samples were degassed by four freeze-thaw cycles (P < .005 cm Hg), using liquid nitrogen to freeze, and sealed. After attaining room temperature the samples were photolyzed to 4.1% conversion. Vpc analysis of the photolyzed samples yielded ratios of (counts acetophenone/ counts tetradecane) which represent the relative quantum yields (00 and e) of acetophenone in the samples. a counts aceto henone °o counts tetragecane (313”k sample) a counts aceto henone . o EEEfitE‘tEtFEfiEEEfiET' (Samples conta1ning quencher) The results are summarized in Table LXXXIII. The Stern-Volmer equation was plotted using the relative quantum yields as explained in the Results Section. Pfifisu amla‘unan-e‘ hn‘! ii 1’ 1 65 B. Quantum yield determinations. Sample tubes containing 0.1 M butyrophenone and a known concentration of tetradecane were photolyzed together with sample tubes containing 0.1 M valerophenone and a known concentration of tetradecane in a merry-go-round assembly which insures equal incident light on sample tubes. Because 0.1 M solutions of these ketones have absorbances greater than 2, essentially all of the incident light was absorbed. A comparison of the amounts of acetophenone formed gave the relative quantum yields of the two ketones. Since the quantum yield for acetophenone formation from valerophenone is 0.3353, the quantum yield from butyrophenone could be calculated. C. Ketone disappearance studies. Chemical quenching was expected to lead to products involving butyrophenone at least some of the time. Consequently, measurement of the ketone which disappears but cannot be accounted for by acetophenone or cyclobutanol appearance gives a minimum value for the amount of chemical quenching occuring. Sample tube preparation was the same as for the quenching runs except that higher concentrations of tetradecane and olefin were used. Higher tetradecane concentration was used so that the ratios of ketone/ tetradecane obtained from vpc analysis would be kept as near unity as possible in order to reduce error. High olefin concentrations were used to maximize the ketone-olefin interaction. Olefin concentrations estimated to be sufficient to quench 50-90 percent of the triplet reaction were used. The tubes were photolyzed long enough to ensure significant ketone disappearnace. The composition of the samples and the results from the vpc analysis are given in Tables XXI - XXV. Additional peaks appeared in the vpc traces, especially for cyclohexene, but these products were not identified. In order to determine the minimum fraction of quenching due to chemical quenching (CQ), butyrophenone disappearance (-8) not accounted for by acetophenone (A) and cyclobutanol (CB) appearance divided by the butyrophenone triplets quenched (Tq) was calculated. fraction CO = ”B ' 4A + CB) (79) q Butyrophenone disappearance was calculated from the ratios of counts of butyrophenone/tetradecane from vpc analysis. The acetophenone yield was calculated similarly and the total yield of acetophenone plus cyclobutanol was calculated by dividing the acetophenone yield by 0.8553. Tq was calculated by first finding the triplets produced, To’ and subtracting the triplets reacted, TR. T=T-T q o R (80) TR was calculated by dividing the yield of acetophenone and cyclobutanol by 0.38 since it was known that only 0.38 of the biradicals formed from triplet butyrophenone yield these productsS“. TR 3 my. . (81) T0 was then calculated by using the Stern-Volmer relationship with the value of qu determined from quenching experiments. 41-:- --.-—-. h .hvaum 003.015 ucocozn0L>d=n\oco—>.:umo...o_.:uu¢.uoh Lem mo—QEow .axx H.362. nlllua-.1-..-1n11.11111.1 1(1th me." map. umeo. oao. pop. o¢.p omp. ammo. oeo. Pop. m~.P omm. ammo. ovo. Pop. mo.p mmm. mppo. oao. pop. mcoomvacpok mpcaoml mcmuoumcumh mucamp wcocmgnogxuzm mucaou m:o=o:noumu< mucaou ncwmoFOH mocmooumeuwhu mmcocmnaogxuamg .xvzum ensues; ococogaogxu:n\ocmpxgumosopgorah Low mmanmm .anx m4m<~ 67' Fm.p NNP. pro. o¢o. can. me.~ h¢—. mmpo. oco. cop. mm.P amp. cope. oeo. cop. -.— opm. onmoo. oeo. cop. ocmuoumgaohlmuczou accumuocumh mucamu mcocmgaoeauam mucaou o:o:o:aoaou< nuance Heywopou mmcmuoumguopu Hococognogauamu .auzum postage mcocmsqoexa=a\mcmpanuooeopgumeamh Low mannEmm .Hxx m4m<~ 68 1.. 1. v. 6::5111111111851e o~.¢ map. no.F emmo. Now. nm.¢ mop. omw. ammo. Now. mm.m omm. awn. vmwo. Now. mm.m oem. wme. emmo. Now. on.” pom. arm. nmmb. mmmwl mmumwmumuuwsmmwmumou wcocw; ouou<.mu==ou HaemopoH Hocmuovmguupu monocognoczuamg xvaum pusvoca ococognoeau:n\w=mxm;oFuzu com mu—qum m elm F. E. 28. 2:. ee.~ Rep. oNN. memo. oop. o¢.~ mop. mop. memo. cop. _m.w __m. opp. mwmb. our. mecca; on gum muczou «coca; pau< mucaou mewmopou Hocmuoumcpmhg monounsaoLAuzmg avaum unavoca ococmgnocxu=a\m=au=nuwuFaguozum Low mansmm a. m me. an. F 38o. 8d. mm.m men. mo.p mmmoo. mac. m¢.m mom. Rpm. mmaoo. moo. 11111111LwRhw111111111111111111bpph111111. mmm. Lawmmfi .mnb. ficwmupou Hocmuouucuohg monocozaosxuamu ozone; as pam mucsou mcocog opou< mucaou auaum guano»; wcocozaogxu=n\m=ou:unumupchmzleummm Lou mmpnsam .Hunxx m4m . C I O 0 > C: (La Ca C; C. S. Nakagawa and P. Sigal, J. Chem. Phys., 88, 3277 (1970). G. S. Hammond, N. J. Turro and P. A. Leermakers, J. Phys. Chem., 88, 1144 (1962). R. E. Rebbert and P. Ausloos, J. Am. Chem. Soc., 81, 5569 (1965). J. Saltiel, K. R. Neuberger and M. Hrighton, J. Am. Chem. Soc., 81, 3658 (1969). H. Reusch, J. Org. Chem., 81, 1882 (1962). E. H. Gold and O. Ginsberg, Angew. Chem., Z8, 207 (1966). N. J. TUrro, P. Hriede, J. C. Dalton, D. R. Arnold and A. H. ‘ Glick, J. Am. Chem. Soc., 82, 3950 (1967). J. S. Bradshaw, J. Org. Chem., 81, 237 (1966). N. C. Yang, M. Mussin and D. R. Coulson, Tet. Letters, 1525 (1965). S. H. Schroeter and C. M. Orlando, Jr., J. Org. Chem., 88, 1181 (1969). E. S. Huyser and L. Kim, J. Org. Chem., 88, 94 (1969); C. Walling and E. S. Huyser, Org. Reactions, 18, 91 (1963). S. M. Japar, M. Pomerantz and E. H. Abrahamson, Chem. Phys. Letters, 8, 137 (1968). 57. 58. 59. 60. 61. 62. 63. 65. 66. 67. 68. 69. 70. 71. 72. 76 REFERENCES (Continued) P. deMayo, J. B. Strothers and W. Templeton, Can. J. Chem., 38, 488 (1961). N. C. Yang, J. I. Cohen and A. Shani, J. Am. Chem. Soc., 39, 3264 (1968). N. C. Yang, R. Loeschen and D. Mitchell, J. Am. Chem. Soc., F“; 88, 5465 (1967). R. A. Caldwell and S. P. James, J. Am. Chem. Soc., 88, 5184 (1969). R. A. Caldwell, J. Am. Chem. Soc., 88, 1439 (1970). FFru" +~ _ i A. M. Braun, W. B. Hammond and H. G. Cassidy, J. Am. Chem. Soc., 88, 6196 (1969). A. A. Lamola and G. S. Hannond, J. Chem. Phys., 88, 2129 (1965). P. J. Wagner and G. 5. Hammond, J. Am. Chem. Soc., 88, 1245 (1966). P. J. Wagner, ibid., 89, 5898 (1967); P. J. Wagner and A. E. Kemppainen. ibid., 88, 5896 (1968). G. 5. Hammond, J. Saltiel, A. A. Lamola, N. J. Turro, J. S. Bradshaw, D. O. Cowan, R. S. Counsell, V. Vogt and C. Dalton, J. Am. Chem. Soc., 88, 3197 (1964). P. J. Wagner and I. Kochevar, J. Am. Chem. Soc., 88, 2232 (1968). D. I. Schuster, A. C. Fabian, N. P. Kong, W. C. Barringer, W. V. Curran and D. H. Sussman, ibid., 88, 5027 (1968). C. Walling and M. J. Gibian, J. Am. Chem. Soc., 81, 3361 (1965). A. D. Wa1sh and P. A. Warsop, Trans. Faraday Soc., 88, 1418, 1425 (1968). M. L. Pautsma, J. Am. Chem. Soc., 81, 2172 (1965). H. J. L. Backstrom and K. Sandros, Acta Chem. Scand., 88, 958 (1962). C. Walling and W. Thaler, J. Am. Chem. Soc., 88, 3877 (1965); C. Walling and V. P. Kurkov, J. Am. Chem. Soc., 88, 4895 (1967). ; 1 d(' 73. 74. 75. 76. 77. 78. REFERENCES (Continued) L. N. Ferguson, J. Chem. Ed., 81, 46 (1970). Ref. 14, p. 309. E. S. Huyser, J. Org. Chem., 88, 3261 (1961). A. D. Walsh and P. A. Warsop, Trans. Faraday Soc., 88, 1418, 1425 (1968). R. S. H. Liu, J. Am. Chem. Soc., 88, 112 (1967). F. G. Moses, R. S. H. Liu, and B. M. Monroe, Mol. Photochem., 1, 245 (1969). v1. APPENDIX 5 " 78 79 a TABLE XXXII. Quenching of Triplet Butyrophenone by 2,5-Dimethyl-2,4-hexadieneb aSampie III; R = 5 x 109 M'Tsec .1 73 Counts Acetophenone 0 [Butyroohenone] [C14H30] [Olefin] x 10 Counts c14H3O 4 I0 .0955 .00259 0 15351 .0955 .00259 .512 1.83 1.35 .0955 .00259 1.024 1.55 1.59 .0955 .00259 1.536 1.35 1.83 .0955 .00259 2.048 1.12 2.20 .0955 .00259 2.560 1.04 2.37 1.Sample I; bkq = 5 x 109 M'1 sec". TABLE xxxm. Quenching of Triplet Butyrophenonea by 2,5-Dimethy1-2,4-hexadieneb 3 Counts Acetophenone o [Butyrophenone] [C14H30] [Olefin] x 10 Counts c14H3O 0 /o .101 .0025 0 T660 .101 .0025 .816 .485 1.36 .101 .0025 1.63 .391 1.69 .101 .0025 2.45 .337 1.96 .101 .0025 3.26 .297 2.22 aSample III;bkq = 5 x 109 M'Tsec'1. TABLE xxxxv. Quenching of Triplet Butyrophenonea by 2,5-Dimethy1-2,4-hexadieneb 37 Counts Acetophenone 0 [Butyrophenone] [C14H30] [Olefin] x 10 C0unts C14H30 4 lo .100 .00232 0' .866 .100 .00232 0 .897 .100 .00232 1.04 .587 1.52 .100 .00232 2.08 .415 2.15 .100 .00232 3.12 .326 2.73 .100 .00232 4.16 .261 3.41 .100 .00232 5.20 .211 4.22 4b .I TABLE XXXV. by 2,5-Dimethy1-2,4-hexadieneb 80 Quenching of Triplet Butyrophenonea . 3 Counts Aceto henone [Butyrophenone] [C14H30] [Olefin] x 10 _——EBEEE§_T;1fififi;—._ 00/0 jfifij .0032 0 .710 .099 .0032 0 .722 .099 .0032 2.16 .334 2.16 .099 .0032 3.24 .259 2.79 .099 .0032 4.32 .245 2.95 .099 .0032 5.40 .206 3.51 aSamp1e II; bkq = 5 x 109 M‘ 1 SEC -1 TABLE XXXVI. Quenching of Triplet Butyrophenonea by 2,5-Dimethy1-2,4—hexadieneb [Butyrophenone] [C14H30] [Olefinlx 103 135%F31133¥¥53335553 40/4 ounts 14H30 .109 .00190 0 2.22 .109 .00190 1.50 1.16 1.91 .109 .00190 3.00 .953 2.33 .109 00190 4.50 .673 3.30 .109 00190 6.00 .610 3.64 .109 00190 7.50 .500 4.44 aSample II; bkq = 5 x 109 M"1 sec-1. TABLE XXXVII. Quenching of Triplet Butyrophenonea by 2,5—Dimethy1-2,4-hexadieneb [Butyrophenone] [C14H30] [Olefin] x 103 Counts Aceto’genone 00/0 ounts 11;Xl_, (086 .00256’ O .630 .086 .00256 0 .616 .086 .00256 .001 .466 .086 .00256 .002 .348 .086 .00256 .003 .289 .086 .00256 .004 .269 aSamp1e 111; bkq = s x 10 9 M- 1 SEC -1 TABLE XXXVIII. Quenching of E:Trif1uoromethylbutyrophenone 81 by 2,5-Dimethyl-2,4-hexadienea . 3 C t A t h [Butyrophenone] [C14H30] [Olefidlx 10 —9!%5%5E§§E%Efi§ggfl§- 00/4 .082 .0025 O .859 .082 .0025 3.52 .506 1.70 .082 .0025 7.04 .385 2.23 .982 .0025 10.6 .292 2.94 akq = 5 x 109 M" sec7Tl TABLE XXXIX. Quenching of E:Trif1uoromethylbutyrophenone by 2,5-Oimethy1-2,4-hexadienea . 3 Counts Aceto henone o [Butyrophenone] [C14H30] [Olef1n] x 10 -—-7§ififiirtafin36-—- 4 /o .096 .00202 O 771.73 .096 .00202 O 1.74 .096 .00202 2.04 1.24 1.40 .096 .00202 4.08 .853 2.04 .096 .00202 6.12 .808 2.15 .096 .00202 8.16 .668 2.61 .096 .00202 10.2 .566 3.08 akq = 5 x 109 M'1 sec71. TABLE XL. Quenching of Triplet Butyrophenonea by Tetrachloroethylene . Counts Aceto henone 0 [Butyrophenone] [C14H30] [Olefin] -——t3EfiE§—ETEFSB———- 4 /4 .100 110259 0 1.53 .100 .00259 .00533 .865 1.77 .100 .00259 .01066 .571 2.68 .100 .00259 .01599 .459 3.34 .100 .00259 .02132 .357 4.29 .100 .002§9 .02665 .291 5.26 at = 1.14 x 10‘7 sec. in"??? A. A. .. 82 TABLE XLI. Quenching of Triplet Butyrophenonea by Tetrachloroethylene . Counts Aceto henone [BUtyrophenone] [C14H30] [Olefin] Counts t1§H30 80;. .095 .00272’ O .953 .095 .00272 O .966 .095 .00272 .0101 .373 2.59 .095 .00272 .0202 .230 4.20 .095 .00272 .0303 .156 6.18 .095 .00272 .0404 .121 7.99 at = 1.14 x 10‘7sec. TABLE XLII. Quenching of Triplet Buterphenonea by Trichloroethylene . Counts Atetophenone [Butyrophenone] [C14H30] [Olefin] Counts C14H3O 40/4 '7100 .00259 O 1.39 .100 .00259 O 1.41 .100 .00259 .010 .821 1.71 .100 .00259 .020 .568 2.47 .100 .00259 .030 .420 3.32 .100 .00259 .040 .339 4.13 .100 .00259 .050 .278 5.03 at = 1.14 x 10'7 sec. TABLE XLIII. Quenching of Triplet Butyrophenonea by Trichloroethylene Counts Acetephenone 0 [Butyrophenone] [C14H30] [Olefin] Counts Cl4H3O 0 lo .101 5500295 0 2.20 .101 .00295 O 2.23 .101 .00295 .0101 1.25 1.78 .101 .00295 .0202 .850 2.61 .101 .00295 .0303 .628 3.54 .101 .00295 .0404 .478 4.65 .101 .00295 .0505 .492__, 5.53 a. . 1.14 x 10‘7 sec. 1 s. '. .h'w TABLE XLIV. 83 Quenching of Triplet Butyrophenonea by gig: and trans-1,2-Dichloroethy1ene Counts Aceto henone o [Butyrophenone] [C14H30] [Olefin] -_CBUHE§_C;EH§;_—— 0 lo .100 .00195’ TT 1. .100 .00185 O 1.82 trans-1,2-dichloroethy1ene .100 .00185 .0086 1.53 1.20 .100 .00185 .0171 1.16 1.59 .100 .00185 .0513 .582 3.16 .100 .00185 0513 .600 3.07 .100 .00185 0855 .392 4.70 gi§;1,2-dichloroethy1ene .100 .00185 .0158 1.57 1.17 .100 .00185 .0158 1.52 1.21 .100 .00185 .0474 .972 1.89 .100 .00185 .0474 .977 1.88 .100 .00185 .0316 .720 2.56 ac = 1.13 x 10'7 sec TABLE XLV. Quenching of Triplet Butyrophenonea by trans-1,2-Dichloroethy1ene . Counts Aceto henone 0 [Butyrophenone] [12141130] [0181.111] W 9 /¢ .0945 .00265 O . .0945 .00265 0 1.02 .0945 .00265 .01005 .861 1.21 .0945 .00265 .02010 .648 1.60 .0945 .00265 .03015 .494 2.10 .0945 .00265 .04020 .420 2.48 .0945 .00265 .05025 .346 3.01 = 1.14 x 10'7 sec TABLE XLVI. 84 Quenching of Triplet Butyrophenonea by trans-1,2-Dich10roethylene [Butyrophenone] _u...‘ [C H . C0unts Acetophenone 14 30] [O‘Ef‘"] Counts 01403 °°/¢ 0.0948 .00259 0 2—08 0 0.0948 .00259 0 2'22 0.0948 .00259 .010 1'90 1 0.0948 .00259 .020 1'33 1°21 0.0948 .00259 .030 1'10 2'02 8.0948 .00259 .040 :89] 2'49 a .0948 _7 .00259 .050 .733 3,03 1 = 1.14 x 10 sec. TABLE XLVII. Quenching of Triplet Butyrophenonea by 918:1,2-Dichloroethylene gCounts Acetophenone 0 [Buterphenone] [C14H30] [Olefin] Counts 014830 4 /0 0.100 .00282 O 1.69 0.100 .00282 0 1.71 0.100 .00282 .010 1.63 1.04 0.100 .00282 .020 1.36 1.25 0.100 .00282 .030 1.16 1.46 0.100 .00282 .040 .994 1.71 0.100 .00282 .050 .895 1.90 a1 = 1.14 x 10'7 sec. TABLE XLVIII. Quenching of Triplet Butyrophenonea by 518:1,2-Dichloroethy1ene . Counts Aceto henone [Butyrophenone] [CI4H30] [Olefin] Counts C13H30 ¢°/¢ .126 .00250 0 1.29 .126 .00250 O 1.31 .126 .00250 .05 .574 2.27 .126 .00250 .10 .324 4.02 .126 .00250 .15 .219 5.94 .126 .00250 .20 .176 7.38 3. . 1.14 x 10'7 sec. 'k‘ I 85 a TABLE XLIX. Quenching of Triplet Butyrophenone by trans-1,Z-Dichloroethylene Counts Acetophenone - 0 [Buterphenone] [C14H30] [Olefin] Counts C14H30 0 /4 .0945 .00265 0 1:04 .0945 .00265 0 1.02 .0945 .00265 .01005 .961 1.21 .0945 .00265 .02010 .648 1.60 .0945 .00265 .03015 .494 2.10 .0945 .00265 .04020 .420 2.48 .0945 .00265 .05025 .346 3.01 a1 = 1.14 x 10'7 sec TABLE L. Quenching of Triplet Butyrophenonea by trans-1,2-Dichloroethylene . Counts Acetophenone 0 [Butyrophenone] [C14H30] [Olefin] Counts Cl4H30 0 /4 .0948 .00259 O 2.08 .0948 .00259 0 2.22 .0948 .00259 .010 1.90 1.07 .0948 .00259 .020 1.38 1.61 .0948 .00259 .030 1.10 2.02 .0948 .00259 .040 .891 2.49 .0948 .00259 .050 .733 3.03 at = 1.14 x 10'7sec TABLE LI. Quenching of Triplet Butyrophenonea by 2,3-Oimethy1-2-buteneb . Counts Acetophenone 0 [Butyrophenone] [C14H30] [Olefin] Counts C14“30 0 lo .100 .00238 0 1.02 .100 .00238 O 1.06 .100 .00238 .00875 .768 1.37 .100 .00238 .0175 .635 1.66 .100 .00238 .0263 .545 1.93 .100 .00238 .0350 .465 2.26 .100 .00238 .0438 .387 2.71 a. . 0.80 x 10' 7 bPurified by prep vpc, then distilled. TABLE LII. Quenching of Triplet Butyrophenonea by 2,3-Dimethy1—2-buteneb . Counts Aceto henone o [Butyrophenone] [C14H30] [O1ef1n] __—C603t§—C;EHSB—_—' o lo .100 .00252, 0 .711 .100 .00252 0 .712 .100 .00252 00916 .503 1.41 .100 .00252 .0183 .408 1.74 .100 .00252 .0275 .352 2.02 .100 .00252 .0366 .303 2.35 .100 .00252 .0458 .258 2.76 a1 = 0.80 x 10'7 sec; bPurified by prep vpc, then distilled. TABLE LIII. Quenching of Triplet Butyrophenonea by 2,3-Dimethy1-2-buteneb . Counts Aceto henone o [Butyrophenone] [C14H30] [Olefin] —-—tafifiiir1;ifi¥i;——— 4 lo 0.100 .00264 0’ 1.14 0.100 .00264 .0127 .626 1.82 0.100 .00264 .0254 .483 2.36 0.100 .00264 .0381 .378 3.02 0.100 .00264 .0635 .270 4.22 at = 1.14 x 10'7 sec; bPurified by prep vpc. TABLE LIV. Quenching of Triplet Butyrophenonea by 2,3-Dimethy1-2-buteneb . Counts Aceto henone 0 [Butyrophenone] [C14H30] [Olefin] __—Caifi?§_ffiffifii;___ o lo .100 .002527 0 1.23 .100 .00252 0 1.24 .100 .00252 .00742 .912 1.36 .100 .00252 .0223 .697 1.78 .100 .00252 .0223 .697 1.78 .100 .00252 .0371 .567 2.19 .100 .oozggyi .0371 .583 2.13 at = 0.80 x 10'7 sec; bPurified by prep vpc, then distilled. 87 TABLE LV. Quenching of Triplet Butyrophenonea by 2-Methy1-2-buteneb . Count§4Aceto henone [Butyrophenone] [C14H30] [Olefin] Counts C12H30 40/0 .0995 .00280 0 .905 .0995 .00280 O .841 .0995 .00280 .0112 .695 1.30 .0995 .00280 .0224 .648 1.39 .0995 .00280 .0336 .598 1.51 .0995 .00280 .0560 .498 1.82 5-5 at = 1.14 x 10"7 sec; bPurified by prep vpc. 1 a | . TABLE LVI. Quenching of Triplet Butyrophenone by 2-Methy1-2-buteneb . CountsAcetophenone [Butyrophenone] [C14H30] [Olefin] Counts c14H30 00/0 .100 .00252? 0 .651 .100 .00252 O .630 .100 .00 52 .00752 .424 1.51 .100 .00252 .02256 .331 1.94 .100 .00252 .0376 .271 2.34 .100 .00252 .0337 .430 1.49 .100 .00252 .1011 .280 2.29 .100 .00252 .1685 .226 2.83 at = 0.80 x 10'7 sec; bPurified by prep VPC- TABLE LVII. Quenching of Triplet Butyrophenonea by Z-Methyl-Z-buteneb . Counts Aceto henone [Butyrophenone] [C14H30] [Olefin] Counts cliHBO 40/0 .100 .00238 O 1.02 .100 .00238 O 1.06 .100 .00238 .0225 .800 1.31 .100 .00238 .0450 .718 1.46 .100 .00238 .0675 .604 1.74 .100 .00238 .0900 .543 1.93 .100 .00238 .1125 .464 2.26 9. . 0,30 x 10'7 sec; bPurified by prep vpc, then distilled. TABLE LVIII. 88 by 515:3-Hexene Quenching of Triplet Butyrophenonea [Butyrophenone] [C H ] [Olefin] Counts Aceto’hénone 14 30 14H30 .099 .00326 0 1.30 .099 .00326 0 1.44 .099 .00326 .0942 1.07 .099 .00326 .283 .661 .099 .00326 .471 .531 a1 = 0.99 x 10‘ sec; bDistilled from sodium under N2. a a. = 1.13 x 10 TABLE LIX. Quenching of Triplet Butyrophenone by gig; and trans-3-Hexeneb . Counts Acetophenone [Butyrophenone] [C14H3o] [Olefin] Counts C14H3o .0950 .00213 0 . .0950 .00213 0 1.35 gigf3-Hexene .0950 .00213 .097 .965 l. .0950 .00213 .194 .762 1. .0950 .00213 .582 .419 3. .0950 .00213 .582 .422 3. .0950 .00213 .970 .290 4. trans-3-Hexene .0950 .00213 0756 .18 1. .0950 .00213 .151 .988 1. .0950 .00213 .454 .920 1. 0950 .00213 .454 .852 1. .0950 .00213 .756 .732 1. bPurified by prep vpc, then distilled. TABLE LX. Quenching of Triplet Butyrophenonea by trans-4-octeneb . counts Aceto henone 0 [Butyrophenone] [C14H30] [Olefin] ———tafifi{§—t;£HSB———- o lo .101 .00242 O 71.15 .101 .00242 .150 .620 1.86 .101 .00242 .300 .568 2.02 .101 .00242 .450 .577 1.99 .101 .00242 .600 .517 2.22 .101 .00242 .750 .460 2.50 at = 1.14 x 10'7 sec; bPurified by prep vpc. TABLE LXI. Quenching of Triplet Butyrophenonea by c1_s-4-Methyi-2-penteneb . Counts Aceto henone o [Butyrophenone] [C14H30] [Olefin] -—CBGHT§—C;§FSB_-' o /4 .104 .00278 0 1:18 .104 .00278 O 1.23 .104 .00278 .275 1.00 1.23 .104 .00278 .550 .809 1.52 .104 .00278 .825 .725 1.70 .104 .00278 1.10 .635 1.94 at = 1.14 x 10-7 sec; bPurified by prep vpc. TABLE LXII. Quenching of Triplet Butyrophenonea by trans-4-Methy1-2-penteneb . Counts Aceto henone o [Butyrophenone] [CI4H30] [Olefin] ‘-—CEUfit§_C;Efi§6__— o lo .102 .00287 0 .870 .102 .00287 0 .987 .102 .00287 .574 .790 1.25 .102 .00287 .861 .678 1.46 .102 .00287 1.435 .629 1.57 at = 0.99 x 10"7 sec; bPurified by prep vpc. TABLE LXIII. Quenching of Triplet Butyrophenonea by trans-4—Methy1-2-penteneb . Counts Aceto henone o [Butyrophenone] [C14H30] [Olefin] ___C60315_C;EF§6__—' 0 /¢ T106 .00164 O 1.839 .106 .00164 0 1.85 .106 .00164 .387 1.38 1.34 .106 .00164 .387 1.60 1.16 .106 .00164 1.16 1.22 1.52 .106 .00164 1.93 .961 1.92 aT = 0.99 x 10"7 sec; bDistilled on spinning band column. TABLE LXIV. Quenching of Triplet Butyrophenonea by gi§;2-Penteneb [But r0 henone] [C H ] [Olefin] 999%EE—592392h9fl992- 00/4 Y p 14 30 ounts 81 41130 .104 .0025 O .502 .104 .0025 O .502 .104 .0025 .100 .311 1.61 .104 .0025 .200 .236 2.13 .104 .0025 .600 .114 4.40 at = 0.80 x 10"7 secZAbPurified by prep vpc. TABLE LXV. Quenching of Triplet Butyrophenonea by gig: and trans-2-Pentene . Counts Acetophenone o [Butyrophenone] [C14H30] [Olefin] Counts C14H30 0 /¢ .100 .00252 O .879 .100 .00252 O .910 gj§;2-pentene .100 .00252 .065 .830 1.10 .100 .00252 .130 .600 1.52 .100 .00252 .390 .342 2.68 .100 .00252 .650 .250 3.64 trans-Z-pentene .100 .00252 .078 .751 1.21 .100 .00252 .155 .712 1.28 .100 .00252 .465 .633 1.71 .100 .00252 .775 .445 2.05 aT = 0.80 x 10.7 sec; bPurified by prep vpc, then disti11ed. TABLE LXVI. Quenching of Triplet Butyrophenonea by gig: and trans-Z-Pentene . Counts Aceto henone o [Butyrophenone] [C14H30] [01Ef1n] W 45 /¢ .100 .00238: O .585 .100 .00238 O .552 gig:2-pentene .100 .00238 .115 .353 1.66 .100 .00238 .230 .281 2.08 .100 .00238 .345 .218 2.68 .100 .00238 .460 .176 3.33 .100 .00238 .575 .158 3.64 trans-Z-pentene .100 .00238 .103 .462 1.27 .100 .00238 .206 .429 1.36 .100 .00238 .309 .384 1.52 .100 .00238 .412 .343 1.71 .100 .00238 .515 .304 1.93 at = 0.80 x 10'7 sec; bPurified by prep vpc, then disti11ed. TABLE LXVII. Quenching of Triplet Butyrophenonea by gig: and trans-2-Penteneb . Counts Aceto henone o [Butyrophenone] [C14H30] [Olefin] ——-CBUfi?§-C;EFSB___' o lo .0950' .00213 0 1.40 .0950 .00213 0 1.33 gig:2-pentene .0950 .00213 .184 .695 2.01 .0950 .00213 .553 .344 4.07 .0950 .00213 .921 .208 6.73 trans-2-pentene .0950 .00213 .116 1.14 1.23 .0950 .00213 .231 .990 1.41 .0950 .00213 .693 .589 2.38 .0950 .00213 .693 .638 2.19 .0950 .00213 1.16 .450 3.11 .7 at 1.13 x 10 sec; Bthified by prep vpc, then distilled. 92 TABLE LXVIII. Quenching of Triplet Butyrophenonea by trans-2,3,5,5-Tetramethy1-3-hexene . ’Counts Aceto henone 0 [Butyrophenone] [C14H30] [Olefin] ___95931§_51§“30__— 4 /4 .100 .00238, O .600 .100 .00238 0 .640 .100 .00238 .0825 .563 1.14 .100 .00238 .165 .490 1.31 .100 .00238 .495 .364 1.76 .100 .00238 .495 .329 1.95 .100 .00238 .825 .370 1.73 at = 0.80 x 10'7 sec. TABLE LXIX. Quenching of Triplet Butyrophenonea by 2-Methy1-1-buteneb . Counts Aceto henone o [Butyrophenone] [C14H30] [Olefin] __-CEUEE§—C;§HEB-_—— 4 /4 .104 .00229 0 1.97 .104 .00229 .196 1.07 1.84 .104 .00229 .246 1.18 1.67 .104 .00229 .295 .968 2.04 81 = 1.14 x 10'7 sec; bPurified by prep vpc. TABLE LXX. Quenching of Triplet Butyrophenonea by 2-Methy1-1-buteneb . Counts Aceto henone 0 [Butyrophenone] [C14H30] [Olefin] -_'CBEfi?§-C;SHSB——_' 4 /4 .101 .00270 O 5899 .101 .00270 0 .915 .101 .00270 .090 .672 1.36 .101 .00270 .180 .625 1.46 .101 .00270 .270 .515 1.71 .101 .00270 .360 .390 2.34 .101 .00270 .450 .407 _ 2.25 a1 = 1.14 x 10'7 sec; bPurified by prep vpc. TABLE LXXI. Quenching of Triplet Butyrophenone by 1-Penteneb a . Counts Aceto henone 0 [Butyrophenone] [C14H30] [Olefin] __—CBUfif§—C;£FSE_—_h 4 /4 .101 .00278 O 1.34 .101 .00278 0 1.35 .101 .00278 .505 .826 1.63 .101 .00278 1.515 .550 2.46 .101 .00278 2.525 .410 3.29 .101 .00278 2.525 .384 3.52 a1 = 1.14 x 10’!7 sec; bPurified by prep vpc. TABLE LXXII. Quenching of Triplet Butyrophenonea by Bicyclo[4.2.0]oct-7-ene Counts Aceto henone 0 [Butyrophenone] [C14H30] [Olefin] ——_CEUHT§_C;§Hga_—_ 4 /4 .100 .0025 O .847 .100 .0025 .180 .340 2.49 at =1.14 x 10'7 sec. TABLE LXXIII. Quenching of Triplet Butyrophenonea by Bicyclo[4.2.0]oct-7-ene . Counts Acetoghenone 0 [Butyrophenone] [C14H30] [Olefin] Counts C14H30 4 /4 .100 .00292 O .502 .100 .00292 0 .494 .100 .00292 .334 .127 3.96 at = 1.14 x 10'7 sec. TABLE LXXIV. Quenching of Triplet Butyrophenone by Norbornene a Counts Acetophenone 0 [Butyrophenone] [C14H30] [Olefin] [Counts C14H30 4 /4 .100 .00252 0 1.23 .100 .00252 O 1.24 .100 .00252 .275 .729 1.70 .100 .00252 .275 .732 1.69 .100 .00252 .459 .524 2.37 .100 .00252 .459 .492 2.52 at = 0.80 x 10'7sec. TABLE LXXV. Quenching of Triplet Butyrophenonea by Norbornene [But r0 henone] [c H 1 [Olefin] C°“"t5 ACEtQPhe"°"e 00/4 y, p 14 30 Counts CMH30 .100 .00252 0 .651 .100 .00252 0 .630 .100 .00252 .0846 .613 1.04 .100 .00252 .254 .384 1.67 .100 .00252 .423 .266 2.41 at = .80 x 10'7sec. 95 TABLE LXXVI. Quenching of Triplet Butyrophenonea by Cyclopentene . Counts Aceto henone o [Butyrophenone] [CI4H30] [Olefin] ——-Tifififii:ifififiSB———- 4 /4 .116 .00232 0 1.16 .116 .00232 0 1.20 .116 .00232 .1915 .552 2.18 .116 .00232 .1915 .553 2.18 .116 .00232 .5745 2.71 4.43 .116 .00232 .5745 2.78 4.32 a1 = 1.14 x 10'7 sec. TABLE LXXVII. Quenching of Triplet Butyrophenonea by Cyclopentene . Counts Aceto henone 0 [Butyrophenone] [C14H30] [Olefin] ———Caifit§_C;Efi§;__— 4 /4 .100 .00358 0 .641 .100 .00358 O .635 .100 .00358 .0965 .391 1.65 .100 .00358 .1930 .296 2.15 .100 .00358 .2895 .227 2.81 .100 .00358 .3860 .186 3.43 a1 = 1.14 x 10'7 sec. TABLE LXXVIIL Quenching of Triplet Butyrophenonea by Cyclohexeneb . C [Butyrophenone] [C14H3o] [Olefin] —99%%%fi%§§%$EE§§9£§- 40/4 .103 .00242 0 2141 '— .103 .00242 O 2.40 .103 .00242 .555 .875 2.76 .103 .00242 .925 .639 3.77 .103 .00242 1.11 .550 4.38 7 a1 = 1.14 x 10' sec; bPurified by spinning bond distillation, then prep vpc. o .1 ‘5 TABLE LXXIX. Quenching of Triplet Butyrophenonea by Cyclohexeneb . Counts Aceto henone [Butyrophenone] [C14H30] [0180111] W 00/41 .101' .00202 0 1.63 .101 .00202 0 1.60 .101 .00202 .148 1.05 1.55 .101 .00202 .444 .551 2.96 .101 .00202 .740 .382 4.27 a1 = .99 x 10' bPurified by prep vpc. TABLE Lxxx. Quenching of Triplet Butyrophenonea by Cycl ohexeneb [But ro henone] [C H ] [Olefin] 992%35-AE§%QEEEEQEE 40/4 Y P 14 30 ounts 14H30 .100 .00166' 0 1.29 .100 .00166 0 1.25 .100 .00166 .181 .827 1.56 .100 .00166 .181 .755 1.71 .100 .00166 .543 .451 2.86 .100 .00166 .543 .391 3.30 .100 .00166 .907 .271 4.76 .100 .00166 .907 .285 4.53 at = 0.99 x 10'7 sec; bRefluxed with maleic anhydride, distilled on spinning band column. TABLE LXXXI. Quenching of Triplet Butyrophenone by Cyclohexeneb a - _________.__Jl_____. [Butyrophenone] [C14H30] [Olefin] C°"2§fin§§e5:4fl:3°ne 40/4 .104 .0025 0 .529 .104 .0025 0 .522 .104 .0025 0.100 .321 1.65 .104 .0025 0.200 .274 1.93 .104 .0025 0.600 .155 3.41 .104 .0025 1.00 .100 5.29 aT = 0.80 x 10'7 sec; by prep vpc. b Distilled on spinning band column, then purified 97 TABLE LXXXII. Quenching of Triplet Butyrophenone by Cycloheptene a Counts Acetoghenone o [Butyrophenone] [C14H30] [Olefin] Counts C14H30 4 /4 .102 .00288’ O .950 .102 .00288 0 1.01 .102 .00288 .080 .608 1.66 .102 .00288 .120 .500 2.02 .102 .00288 .160 .423 2.38 .102 .00288 .240 .326 3.10 at =1.14 x 10'7 sec. TABLE LXXXIII.Quenching of Triplet Butyrophenonea by Cyclooctene . Counts Aceto henone 0 [Butyrophenone] [C14H30] [Olefin] _——CBUHT§—C;EF§6_—_' 4 /4 .107' .00259 0 .823 .107 .00259 O .841 .107 .00259 .0404 .633 1.33 .107 .00259 .0808 .474 1.77 .107 .00259 .1212 .404 2.08 .107 .00259 .1616 .327 2.57 .107 .00259 .2020 .290 2.90 aT = 1.14 x 10'7 sec. TABLE LXXXIV. Quenching of Triplet Butyrophenonea by 1,4-Cyclohexadiene . C t Ac to henone [Butyrophenone] [C14H30] [Olefin] ‘22999999291E036—_— 40/4 .099 .0026 0 .687 .099 .0026 O .689 .099 .0026 .0395 .445 1.54 .099 .0026 .0790 .369 1.87 .099 .0026 .0790 .378 1.82 at = 0.80 x 10'7 sec. 98 TABLE LXXXV. Quenching of Q:Trifluoromethylbutyrophenonea by gig:2-pentene . Counts Aceto henone o [Butyrophenone] [C14H3o] [Olefin] __—Cafifit§—CTEFES___ 4 /4 .082 .0025’ O .975 .082 .0025 0 .968 .082 .0025 .0665 .852 1.14 .082 .0025 .133 .720 1.35 .082 .0025 .399 .525 1.86 .082 .0025 .665 .353 2.76 a1 = .36 x 10'7 sec. TABLE LXXXVI. Quenching of p_:Trif1uoromethylbutyrophenonea by 2-Methy1-2-butene . C t A t h [Butyrophenone] [C14H30] [Olefin] _2!%9999529$Efi§§2flg 40/4 .082 .0025 0 .975 .082 .0025 0 .968 .082 .0025 .0246 .785 1.24 .082 .0025 .0492 .688 1.41 .082 .0025 .1476 .423 2.29 .082 .0025 .1476 .423 2.29 .082 .0025 .1968 .353 2.75 aT = .36 x 10'7 sec. a TABLE LXXXVII. Quenching of g:Trifluoromethylbutyrophenone by Norbornene Counts Aceto henone o [Butyrophenone] [C14H3O] [Olefin] ‘__CBGEE§-CT§F§6__— 9 /¢ .096 .00202 O 1.73 .096 .00202 O 1.74 .096 .00202 .179 1.16 1.50 .096 .00202 .358 .825 2.11 .096 .00202 .537 .704 2.47 .096 .00202 .716 .596 2.92 at = 0.6 x 10'7 sec. r: Willa-El