System analysis of model calculations of structure and spectra of tautomer dihydroxy 5x-uracil
5x-substituted uracil (X = F, Н, Cl, СH3) is one of the tautomer form. The work presents regularities of the shift of vibrational spectrum bands of the mentioned compounds, defines its spectrum identification characteristics of their possible conformers in the condensed state. Considered models of conformers that are different by the values of dihedral angles and bond lengths. We used DFT/B3LYP method with bases G-311G(p,d) and G-311+G(p,d) in calculating the optimized structure and vibrational frequencies. The dimerization leads to a change in the lengths of valence bonds by ~ 0,2 Å, that causes displacement of oscillation bands of valence bonds C=O in the long-wavelength range by ~ 30–70 cm-1. For identification of conformers we can use different in the values of the intensity in the range above 100 cm-1. Influence of the substitute results in the band shift by ~ 30 cm-1, that enables us to make a conclusion about the local influence of the substitute on the force field of the azacyclic ring.