Theoretical Study of Stability, Tautomerism, Equilibrium Constants (pKT) of 2-Thiouracil in Gas Phase and Different Solvents (Water and Acetonitrile) by the Density Functional Theory Method

A density functional theory (DFT) calculations were carried out to investigate the relative energies, equilibrium constants and dipole moments of 2-thiouracil in the gas phase and in solutions with different polarities. Solvent effects were examined by means of the self-consistent reaction field (SCRF) method. All possible tautomers are optimized at the B3LYP/6- 311++G (d,p). All calculations indicate that the most stable tautomer for both species, in the gas phase as well as in solution, has the 2TU1 form.In addition to calculate the thermodynamic properties and the inter conversion equilibrium constants for all tautomers. The molar transfer Gibbs energies of ∆∆Gt0 (solvent1- solvent 2), determines the solvent effect on the position of the equilibrium.