Studies on tautomerism in the triazoline dione

Abstract

The chemical properties of the triazoline dione have been extensively studied. The relative stability of three tautomers in the gas phase and solution (using PCM model) are evaluated using HF and DFT methods and compared with MP2 level using different basis sets. The results of the calculations indicate that 4H-1,2,4-triazole-3,5-dione (K form) is more stable in the gas phase than in solution. In addition, the transition states of proton transfer reaction is calculated. The vibrational frequencies and corresponding normal mode assignments of 4H-1,2,4-triazole-3,5-dione and 5-hydroxy-3H-1,2,4-triazol-3-one (E1 form) are also theoretically examined. In addition, the variation of dipole moments and charges on atoms with change of solvent is studied. Specific solvent effects with addition of one molecule of water near the electrophilic centers of three tautomers and the transition state of proton transfer assisted by a water molecule was investigated. Aggregation with water molecules 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.