Investigation of simple and water assisted tautomerism in a derivative of 1,3,4-oxadiazole: A DFT study

Abstract

Investigation of tautomerism and transition states in a derivative of 1,3,4-oxadiazole (A, B, C and D)<br><br>in the gas phase and in solution and in a micro hydrated environment with 1–3 water molecules was<br><br>performed by calculations at the DFT-B3LYP/6-311++G(d,p) level of theory. The solvent effect is taken into account via the self-consistent reaction field (SCRF) method. The geometries of four possible tautomers of 5-amino-1,3,4-oxadiazole-2(3H)-one were optimized in the gas phase and solution with polarized continuum model (PCM). It was found that in the gas phase and different solvents, A and C tautomers are the most stable and unstable forms, respectively.<br><br>The results show that the tautomeric interconversion C to D has the lowest Gibbs free energy changes<br><br>and so the highest equilibrium constant in the gas phase and solution. The equilibrium and rate constants<br><br>of intermolecular tautomerism in the absence and presence of 1–3 molecules of water were also calculated. The calculated results show that the presence of water molecules considerably reduces the<br><br>barrier energy of the various reactions. Therefore, this water-assisted tautomerism can be performed<br><br>fast, especially, with the assistance of two molecules of water.