Photochemical α Cleavage and Free-Radical Reactions of Some Deoxybenzoins

H. G. Heine, W. Hartmann, D. R. Kory, J. G. Magyar, C. E. Hoyle, J. K. McVey, Frederick D Lewis

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Abstract

The effect of α-methyl and α-phenyl substituents on the photochemical α-cleavage reactions of alkyl phenyl ketones has been investigated, α cleavage is the only primary process observed upon irradiation of the deoxybenzoins 1-4 in degassed benzene solution. Photoreduction competes with a cleavage of deoxybenzoin in 2-propanol-benzene solution. The reactions of the benzoyl and benzyl free radicals formed upon α cleavage have been studied in some detail. Spectroscopic and energy transfer data indicate that α cleavage occurs exclusively from the lowest 3n,π* excited state. Triplet lifetimes were measured by Stern-Volmer analysis of product quenching by naphthalene and, for deoxybenzoin, by quenching of room temperature phosphorescence. The effects of substituents upon triplet lifetimes indicate that the rate constants do not depend on the stability of the resulting radicals. From a comparison of the rate constants for photochemical α cleavage of the deoxybenzoins studied and the rate constants for thermolysis of corresponding peresters it is concluded that the transition state for α cleavage resembles the excited ketone rather than the radical pair.

Original languageEnglish (US)
Pages (from-to)691-698
Number of pages8
JournalJournal of Organic Chemistry
Volume39
Issue number5
DOIs
StatePublished - Mar 1 1974

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Free radical reactions
Rate constants
Benzene
Ketones
Quenching
Phosphorescence
Thermolysis
2-Propanol
Photochemical reactions
Excited states
Energy transfer
Free Radicals
Irradiation
Temperature
deoxybenzoin

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

Heine, H. G., Hartmann, W., Kory, D. R., Magyar, J. G., Hoyle, C. E., McVey, J. K., & Lewis, F. D. (1974). Photochemical α Cleavage and Free-Radical Reactions of Some Deoxybenzoins. Journal of Organic Chemistry, 39(5), 691-698. https://doi.org/10.1021/jo00919a024
Heine, H. G. ; Hartmann, W. ; Kory, D. R. ; Magyar, J. G. ; Hoyle, C. E. ; McVey, J. K. ; Lewis, Frederick D. / Photochemical α Cleavage and Free-Radical Reactions of Some Deoxybenzoins. In: Journal of Organic Chemistry. 1974 ; Vol. 39, No. 5. pp. 691-698.
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Heine, HG, Hartmann, W, Kory, DR, Magyar, JG, Hoyle, CE, McVey, JK & Lewis, FD 1974, 'Photochemical α Cleavage and Free-Radical Reactions of Some Deoxybenzoins', Journal of Organic Chemistry, vol. 39, no. 5, pp. 691-698. https://doi.org/10.1021/jo00919a024

Photochemical α Cleavage and Free-Radical Reactions of Some Deoxybenzoins. / Heine, H. G.; Hartmann, W.; Kory, D. R.; Magyar, J. G.; Hoyle, C. E.; McVey, J. K.; Lewis, Frederick D.

In: Journal of Organic Chemistry, Vol. 39, No. 5, 01.03.1974, p. 691-698.

Research output: Contribution to journalArticle

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N2 - The effect of α-methyl and α-phenyl substituents on the photochemical α-cleavage reactions of alkyl phenyl ketones has been investigated, α cleavage is the only primary process observed upon irradiation of the deoxybenzoins 1-4 in degassed benzene solution. Photoreduction competes with a cleavage of deoxybenzoin in 2-propanol-benzene solution. The reactions of the benzoyl and benzyl free radicals formed upon α cleavage have been studied in some detail. Spectroscopic and energy transfer data indicate that α cleavage occurs exclusively from the lowest 3n,π* excited state. Triplet lifetimes were measured by Stern-Volmer analysis of product quenching by naphthalene and, for deoxybenzoin, by quenching of room temperature phosphorescence. The effects of substituents upon triplet lifetimes indicate that the rate constants do not depend on the stability of the resulting radicals. From a comparison of the rate constants for photochemical α cleavage of the deoxybenzoins studied and the rate constants for thermolysis of corresponding peresters it is concluded that the transition state for α cleavage resembles the excited ketone rather than the radical pair.

AB - The effect of α-methyl and α-phenyl substituents on the photochemical α-cleavage reactions of alkyl phenyl ketones has been investigated, α cleavage is the only primary process observed upon irradiation of the deoxybenzoins 1-4 in degassed benzene solution. Photoreduction competes with a cleavage of deoxybenzoin in 2-propanol-benzene solution. The reactions of the benzoyl and benzyl free radicals formed upon α cleavage have been studied in some detail. Spectroscopic and energy transfer data indicate that α cleavage occurs exclusively from the lowest 3n,π* excited state. Triplet lifetimes were measured by Stern-Volmer analysis of product quenching by naphthalene and, for deoxybenzoin, by quenching of room temperature phosphorescence. The effects of substituents upon triplet lifetimes indicate that the rate constants do not depend on the stability of the resulting radicals. From a comparison of the rate constants for photochemical α cleavage of the deoxybenzoins studied and the rate constants for thermolysis of corresponding peresters it is concluded that the transition state for α cleavage resembles the excited ketone rather than the radical pair.

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Heine HG, Hartmann W, Kory DR, Magyar JG, Hoyle CE, McVey JK et al. Photochemical α Cleavage and Free-Radical Reactions of Some Deoxybenzoins. Journal of Organic Chemistry. 1974 Mar 1;39(5):691-698. https://doi.org/10.1021/jo00919a024