Vibrational dynamics and molecular structure of 1H- and 3H-1,2,3-triazolo[4,5-b]pyridine and its methyl-derivatives based on DFT chemical quantum calculations

Molecular structure, vibrational energy levels and potential energy distribution of 1H-1,2,3-triazolo[4,5-b]pyridine and 3H-1,2,3-triazolo[4,5-b]pyridine as well as 1H- and 3H-tautomers of 5-methyl-1,2,3-triazolo[4,5-b]pyridine, 6-methyl-1,2,3-triazolo[4,5-b]pyridine and 7-methyl-1,2,3-triazolo[4,5-b]pyridine have been determined using density functional theory (DFT) at the B3LYP/6-31G(d,p) level. In order to obtain good fitting with the experimental values the calculated frequencies have been scaled using the scaling factors 0.96 and 0.975 in the 2800-3500 and 1000-1700 cm−1 region, respectively. The role of the hydrogen bond formation in the stabilization of the structure of the studied triazolo[4,5-b]pyridines has been discussed. The substitution place of the methyl group at the pyridine ring influences the proton position of the NH group at the triazole unit. The 5- and 7-methyl substitution leads to the 3H-tautomeric form whereas the 6-methyl substitution gives the mixture of 1H- and 3H-tautomers.