Theoretical Investigation of Proton Transfer in Thiazolidine-2-thione and Oxazolidine-2-thione via Direct Transition and Self-Assisted and Water-Assisted Tautomerization

Abstract

Thione–thiol transformation of thiazolidine-2-thione and oxazolidine-2-thione via direct transition, as well as self-assisted and water-assisted tautomerization was investigated using the quantum-chemical calculations. The thione complexes are more stable than the corresponding thiols. The calculations revealed that the proton transfer energy barriers are significantly lower in the presence of water molecules. Direct transition is more difficult than the water-assisted and self-assisted processes. The cooperative effects in terms of additive interaction energies and cooperativity factors of the clusters are measured and discussed. The electronic properties of the complexes are analyzed using parameters derived from atoms-in-molecules and natural bond orbital methodologies. Also, the influence of the hydrogen bond on the molecular and topological properties, as well as nuclear magnetic resonance one- and two-bond spin–spin coupling constants are investigated.