Influence of Substituent on Tautomeric Equilibrium Constant in 5(6)-Substituted Benzimidazoles in the Gas Phase

Abstract

For 5(6)-substituted benzimidazoles, for which direct intramolecular interactions between the amidine moiety and substituent are absent, the pK_T values calculated by the AM1 method are well reproduced by differences in the transmission of substituent electronic effects: pK_T=(5.08±0.22)Δσ+(0.00±0.01); these differences result mainly from different transmission of resonance effect: pK_T=(0.04±0.12)σ_α–(0.36±0.10)σ_F–(1.76±0.30)σ_R+(0.00±0.06).