PMR spectra and electronic structures of the neutral bases and cations of thiazolo [3,2-a] -benzimidazole and its methyl derivatives

The PMR spectra of the neutral bases and cations of methyl derivatives of thiazolo[3,2-a]-benzimidazole were studied. The dependence of the chemical shifts on the acid concentration was examined. The investigated system is protonated and N-methylated at the N₉ atom. The structure of the conjugated cation corresponds to considerable delocalization of the effective positive charge to the heteroatoms of the thiazole ring. A satisfactory linear correlation between the corrected chemical shifts and the -electron densities, calculated by the simple MO LCAO method using a coulombic integral for the sulfur atom, h_S=0.9, and the parameters of the Pullman system for the remaining heteroatoms, was observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 937–945, July, 1971.