A theoretical study, using ab initio methods, of tautomerism in 3-amino-1,2,4-triazole in the gas phase and in aqueous solution

Abstract

Ab initio molecular orbital methods have been used to predict the relative energies of the three tautomers of 3-amino-1,2,4-triazole, in the gas phase and in aqueous solution. At the highest level of theory employed [6-31G**(CCSD)//6-31G**(HF)] the 1H and 2H tautomers are essentially isoenergetic in the gas phase, with the 4H tautomer 7 kcal mol^–1 to higher energy. Both the self-consistent reaction field and polarisable continuum models predict differential stabilisation of the 4H tautomer upon hydration. However, neither model is in accord with the relative energies of the hydrated tautomers suggested by ¹⁵N NMR spectroscopic data.