Molecular orbital and experimental studies on the photoinduced decarboxylation of pyrethroid model esters

Abstract

A series of pyrethroid model esters with various substituents in the acid or alcohol moiety have been irradiated by u.v.-radiation (λ > 220 nm). The main reaction is decarboxylation, as evidenced by gas chromatographic (g.c.) and mass spectrometric (m.s.) analyses. In the photoinduced decarboxylation reaction, the substituent effect on the main transition, which occurs via carbonyl excitation, and on the reactivity of a radical intermediate have been examined by semiempirical molecular-orbital calculations (MNDO and CNDO/S). It has been found that the change of benzyl carbon–oxygen bond strength in the excited states is one of the important factors in determining the yield of the decarboxylated product.