Theoretical studies on tautomerism of 1H-pyrazole-5-thiol

Abstract

The chemical properties of the 1H-pyrazole-5-thiol have been extensively studied. In the present study, the relative stability of all tautomers in the gas phase and solution (PCM model) are evaluated at DFT and MP2 levels using the 6-311G++(d, p) basis set. The results suggest that 1H-pyrazole-3-thiol (B2 form) and 1H-pyrazole-5-thiol (A form) are the most stable forms in the gas phase and 1,2-dihydropyrazole-3-thione (C form) and 1H-pyrazole-3-thiol (B2 form) are the predominant tautomers in solution at the DFT and MP2 methods, respectively. In addition, variation of dipole moments in the gas phase and solution, the specific solvent effects with addition of one molecule of water near the electrophilic centers of tautomers, the transition state of proton transfer assisted by a water molecule and the NBO charges of atoms were investigated. In addition, it was found that aggregation with water molecule does not change the order of stability of isomers, but proton-transfer reaction assisted by a water molecule needs less energy than the intramolecular process. .