Electric dipole moments of polyhalogenoaromatic compounds. Part 1. Inductive effects in polychlorobenzenes and polychlorotoluenes

Abstract

The electric dipole moments of 20 polychloro-benzenes and -toluenes have been determined in dilute solution in benzene at 298 K. The departures from additivity in the moments are explained in terms of inductive effects between ortho-substituted (and to a lesser extent meta-substituted chlorine atoms) which lessen the apparent C–Cl bond moment, and similar induction between ortho- or meta-substituted chlorine atoms and methyl groups which enhances the apparent methyl group moment. It has previously been suggested that these departures from additivity are caused by variation in atom polarisation, changing mesomeric effects, or by steric distortion; no evidence is found for these explanations. The possible effects of these electron shifts in the ground state on rates of electrophilic or nucleophilic attack on these molecules are discussed.