Substituent effects in homolytic substitution reactions. The phenylation of some 3-substituted thiophens

Abstract

The homolytic phenylation of some 3-substituted thiophens has been investigated; in addition, isomer ratios and partial rate factors for the phenylation of thioanisole, methyl phenyl sulphone, 2-methylthiothiophen, and 2-methyl-sulphonythiophen have been determined. The isomeric composition of the products and the partial rate factors obtained for the phenylation of 3-substituted thiophens indicate that the main effect of the substituent is to render the two α-positions (2- and 5-) non-equivalent, the former being activated, the latter generally deactivated with respect to an α-position of thiophen. Structure–reactivity relationships are discussed.