Influence of hydration on the protomeric tautomerism in selenium analogue of methimazole: A computational chemistry study

Hydrogen bond assisted proton transfer reactions were investigated in 3-methyl-1H-imidazole-2(3H)-selone (MSeI) and 1H-imidazole-2(3H)-selone (SeI) at B3LYP/6-311++G(2d,2p) level of theory. The B3LYP results predict that the direct proton transfer process in MSeI and SeI is more difficult than the water-assisted one. The results also show that the selone complexes are more stable than corresponding selenol ones. Interaction energies for a single NH⋯Se hydrogen bond in dimers MSeI and SeI are −31.3 and −32.7 kJ/mol, respectively. ZPE-corrected binding energies in the self-association complexes of the MSeI and SeI are greater than the water-associated complexes. The small negative value of H(r) obtained by AIM analysis at B3LYP/6-311++G(2d,2p) level reveals some contribution of sharing interaction (partially covalent) to the Se⋯HN bond in dimers of the MSeI and SeI. AIM data also reveal the partially covalent nature of Se⋯H6 interaction and electrostatic nature of O⋯H5 interaction in water-associated complexes. Results of charge analysis show that the selenium analogue of the methimazole is more nucleophilic than the methimazole. Our results confirm that the selenium analogue of methimazole can exist as a zwitterionic form.