Tautomerism in drugs with benzimidazole carbamate moiety: an electronic structure analysis

Abstract

Several medicinally important compounds carry benzimidazole carbamate moiety. In the scientific literature, these molecules are represented in different tautomeric forms. In this report, conformational and tautomeric preferences were analyzed on the model benzimidazole carbamate (carbendazim), so as to understand the potential energy surface of the title compounds. Quantum chemical calculations have been performed using HF, B3LYP, and MP2 methods in gas phase and solvent phase on model benzimidazole carbamate to understand the conformational and tautomeric preferences. (1) PE surface of amide–imide tautomers, (2) electron distribution, (3) AIM analysis, (4) NBO charges, (5) 1,3-H shift, etc., have been investigated for carbendazim and its conformers. The molecular electrostatic potential (MESP) surfaces of carbendazim have been studied. Further to understand the polymorphism in benzimidazole carbamate, analysis of dimers of carbendazim has been carried out. The results indicate that a neglected tautomer is important and the tautomeric equilibrium is quite subtle in these systems and it should be extensively considered in all studies related to these drugs.