Photochemistry of Methyl-Substituted Butyrophenones

Frederick D Lewis, Terrance A. Hilliard

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120 Scopus citations


The effects of methyl substituents upon the photochemical behavior of butyrophenone have been investigated. ier?-Alkyl phenyl ketones undergo competitive a- (type I) cleavage and type II photoelimination and cyclization. The rate constant for a-cleavage (~1 X 107 sec-1) is considerably slower than for a-cleavage of triplet feri-butyl alkyl ketones owing to a difference in the energetics of the reactions. The reactivity of the aromatic carbonyl triplet state toward 7-hydrogen abstraction is determined primarily by 7-substitution and is less affected by a and β substituents, a substituents increase the percentage of cyclization products whereas β substituents have the opposite effect. The effects of substituents on the behavior of the 1, 4-biradical intermediates are explained in terms of the transition states for biradical cyclization and elimination.

Original languageEnglish (US)
Pages (from-to)3852-3858
Number of pages7
JournalJournal of the American Chemical Society
Issue number11
StatePublished - May 1 1972

ASJC Scopus subject areas

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


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