Photolysis of aromatic thioacid O-esters: the nature of the reactive excited state

Abstract

The experimental evidence for the reaction mechanism for the photolysis of thiobenzoate O-esters is given in detail. The reactions are initiated in the lowest triplet state which was observed by nanosecond flash photolysis and characterized as n-π* on the basis of spectral data. Intramolecular abstraction of a hydrogen atom γ to the thiocarbonyl group is suggested to lead to a short-lived 1,4-biradical intermediate from which both elimination and cyclization products are derived. A set of simple rules is put forward to predict the tendency of a variety of aromatic thioacid O-esters and other thiocarbonyl compounds to undergo Type II photochemical reactions.