Entropic control of photochemical reactivity. The transition state for γ-hydrogen abstraction of alkyl phenyl ketones

Frederick D. Lewis*, Richard W. Johnson, Daniel R. Kory

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

74 Scopus citations

Abstract

The photochemical reactivity of several alkyl phenyl ketones, having similar n,π* triplet energies and γ C-H bond strengths but differing in conformational mobility, has been investigated. Measurements of Arrhenius activation parameters show that the rate enhancements in conformationally restricted molecules are entirely entropic in origin. Rate factors of 5-8 for each internal rotation which must be frozen in the transition state are observed. Primary and secondary kinetic deuterium isotope effects have been measured for photochemical γ-hydrogen abstraction. The results are consistent with an unsymmetrical transition state with less than 50% γ C-H bond breaking. The transition state model for γ-hydrogen abstraction is in accord with experimental results and recent theoretical predictions.

Original languageEnglish (US)
Pages (from-to)6100-6107
Number of pages8
JournalJournal of the American Chemical Society
Volume96
Issue number19
DOIs
StatePublished - 1974

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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