Calculation and analysis of the structure and vibrational spectra of uracil tautomers

The structure and vibrational spectra of twelve tautomers are calculated in the B3LYP/6-311+G(d,p) approximation and analyzed. Spectral manifestations of isomeric uracil transformations into one out of the twelve tautomeric forms and cis— trans- isomeric transformations of the tautomers themselves are considered. All tautomeric transformations are shown to be characterized by the presence of at least one vibration, whose frequency is different by ~ 100-200 cm^-1 from a similar vibrational frequency of the precursor and also by a pronounced change in the intensity of bending vibrations of OH hydroxyl groups and stretching vibrations of CO bonds.