Studies on benzimidazoles. Part VIII. 1H nuclear magnetic resonance study of substituted 2-chloro-1-methylbenzimidazoles

Abstract

A number of benzo-substituted 2-chloro-1-methylbenzimidazoles has been studied by ¹H n.m.r. spectroscopy. It is observed both from the ring and N-methyl proton chemical shifts measured in deuteriochloroform and trifluoroacetic acid solution that conjugation effects are present between substituents and the nitrogen atoms of the heterocyclic ring. Proton–proton coupling constants can be rationalized in terms of additive substituent effects when there are no strong mesomeric interactions between substituents and the heterocyclic ring. Charge densities have been calculated for both σ and π-electrons, and the correlations between charges and chemical shifts show that the substituents also perturb the heterocyclic ring through the σ-skeleton.