Studies on Benzimidazoles . Part VIII. 1H Nuclear Magnetic Resonance Study of substituted 2-Chloro-1-methylbenzimidazoles,

A number of benzo-substituted 2-chloro-1-methylbenziimidazoles has been studied by 1-H NMR spectroscopy. It is observed both from the ring and N-methyl proton chemical shifys measured in CDCl3 and CF3COOH 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 sigma and pi-greek electrons, and the correlations between charges and chemical shifts show that the substituents also perturb the heterocyclic ring through the sigma skleton