Theoretical studies on tautomerism of dihydropyrimidine tautomers

The second-order Moller-Plesset (MP2) and density functional theory (DFT) calculations have been carried out using 6-311++G(d, p) basis set to investigate the tautomerism of all five tautomers of dihydropyrimidine in the gas phase and in the solution. In the gas phase the order of stability was found as: B > C > A > E > D, however changing to more polar solvents this order was changed using polarisable continuum method (PCM). In addition variation of dipole moments and charges on atoms are studied in the gas phase and in solvents. NBO analysis shows that there is a strong interaction between nitrogen lone pairs and double bonds. Specific solvent effect induced slight changes in geometry of rings but the order of stability remained.