Substituent effects in homolytic substitution reactions: phenylation of some 2-substituted thiophens

Abstract

Homolytic substitution of 2-substituted thiophens with phenyl radicals occurs predominantly at the 3- and 5-positions; the ratio of isomers is dependent on the electronegativity of the 2-substituent. Total and partial rate factors for the phenylation reaction relative to the rate of phenylation of thiophen have been determined; halogen substituents deactivate and methyl, methoxycarbonyl and nitro-substituents activate the thiophen ring towards substitution.