Vibrational spectra of 6-methyluracil, 6-methyl-2-thiouracil and their deuterated analogues

FTIR and Raman spectra of 6-methyluracil (6MU), 6-methyl-2-thiouracil (6M2TU) and the deuterated forms were recorded and analysed in the regions 400–4000 cm−1 and 100–4000 cm−1, respectively. The vibrational spectra are assigned using the frequency shifts upon N-deuteration, especially for bands due to NH modes. For both molecules, the isotopic ratio frequency was calculated for each NH/ND vibrations. The sulphur substitution at C2 position in the 6MU molecule has an effect on the N1H and N3H vibration frequencies. The assignments of C2O and C4O modes were supported by the absence of the C2O group in the thio-derivative.