Investigation of Benzimidazoles. 5—transmission of the substituent effects in 2‐substituted 5(6)‐nitrobenzimidazoles studied by ¹H, ¹³C and ¹⁵N NMR spectroscopy

Abstract

Abstract The influence of substituents on the 1 H, 13 C and 15 N NMR chemical shifts of 2‐substituted 5(6)‐nitrobenzimidazoles and their analogues labelled with 15 N in the nitro group was investigated. It was found that the substituent effects are transmitted to the carbon and hydrogen nuclei in positions 4–7 mainly by the resonance mechanism, but to the nitro‐nitrogen atom with approximately equal contributions from the resonance and inductive components. Comparison of the transmission of substituent effects in nitro‐benzimidazoles with para and meta derivatives of nitrobenzene showed that the nitro group seems to be more tightly conjugated with the benzimidazole fragment than with the benzene ring.