Research in the pyrimidine series XXV. Calculation of the normal vibrations of barbituric and 2-thiobarbituric acids

The frequencies and forms of the in-plane normal vibrations of the tricarbonyl forms of barbituric and 2-thiobarbituric acids and their tetradeutero derivatives were calculated. The calculations were made for the C_zv (or C_2v and C_s for barbituric acid) symmetry point group. The principal frequencies observed in the IR spectra of these compounds were assigned with respect to the types of vibrations on the basis of an analysis of the forms of the normal vibrations.