Theoretical and Infrared Matrix Isolation Study of 4(3H)-Pyrimidinethione and 3(2H)-Pyridazinethione. Tautomerism and Phototautomerism

Article abstract of DOI:10.1021/j100159a053

IR spectra of 4(3H)-pyrimidinethione and 3(2H)-pyridazinethione isolated in argon and nitrogen matrices are reported.The thiol and thione tautomeric forms of 4(3H)-pyrimidinethione were found in matrices in relative concentrations ca. 5:1.IR spectra of gaseous sample showed that the ratio of tautomers in matrices corresponds to the gas-phase tautomeric equilibrium.Only the thione form of 3(2H)-pyridazinethione was observed in matrices.UV-vis irradiation of the matrices caused the conversion ot the thione forms of the studied molecules into the thiol forms.The IR spectra of the thione and thiol tautomers were predicted theoretically a t SCF/3-21G^* level, and a comparison ot the predicted and experimentally observed spectra enabled an assignment of most of the observed bands.