A study on pyrazinone and pyrazindiones by using quantum mechanical methods

In this thesis, the stable tautomeric structures of pyrazin-2(1H)-one, pyrazine2,6(1H,3H)-dione, 1,6-dihidropyrazine-2,5-dione have been determined by using standard Gibbs free formation energies (ΔGf) calculated in the aqueous phase by PM7 semi-empirical quantum mechanical method. The acidity constant (pKa) and tautomeric equilibrium constant (KT) values of these structures have been also calculated theoretically. The calculated acidity constant values (pKa) have been compared with the experimental valuesin literature. UV-VIS, IR and NMR spectral calculations of the stable structures have been carried out theoretically by using the density functional theory (DFT) method and the function/basis set combination B3LYP/6-31++G(d,p). The calculated spectral values have been compared with the experimental values in literature. The findings from the calculations have been compared with the literature data. Keywords: Pyrazinone, Pyrazindione, Tautomerism, Acidity constant (pKa), PM7, Density Functional Theory (DFT), NMR, IR, UV-VIS, Spectroscopy