Density functional theory of tautomerism and water-assisted proton transfer of glycoluril

Density functional theory and MP2 methods have been employed to study of proton transfer reaction in annular tautomerization of tetrahydroimidazo4,5-d]imidazole-2,5(1H,3H)-dione (glycoluril). Ten different tautomers are possible for the tetrahydroimidazo4,5-d]imidazole-2,5(1H,3H)-dione. For all molecules, the Gibbs free energy at 0 and 298 K was estimated. In addition variation of dipole moments and charges on atoms are studied in the gas phase and solution, the specific solvent effects with addition of one molecule of water near the electrophilic centers of tautomer and the NBO charges of atoms were investigated. NBO analysis shows that there is a strong interaction between nitrogen lone pairs and double bonds.