Structure and relative stability of neutral, protonated and deprotonated thiazolidine-2-one-4-thione tautomers: DFT calculations

Abstract

Relative stabilities of tautomers and rotamers of neutral, protonated and deprotonated thiazolidine-2-one-4-thione (TZD) were studied theoretically using the B3LYP/6-311++G(2df,2p)//6-311+G(d,p) method of the Density Functional Theory (DFT) in the gas phase and solution. Gas phase calculated relative energies showed good correlation with those obtained in solution. Proton affinities ( PA ), molecular basicities ( GB ) and deprotonation enthalpies (D H dep) of the title compound were calculated at the same level of theory. Moreover, the isomerization processes leading from the most stable adduct to other stable conformers were investigated. The results reveal that the thione–oxo tautomer is the most stable tautomer in all cases and TZD behaves as sulfur base. Consideration of the solvent causes some reordering of the relative stability of the tautomers and a drastic change in the values of PA , GB and D H dep.