Theoretical and experimental study of solvent effects on the structure, vibrational spectra, and tautomerism of 3-amino-1,2,4-triazine

The structure, and vibrational spectra of an important heteroaromatic compound, 3-amino-1,2,4-triazine (3-atz), have been calculated by using B3LYP/6-311++G(d,p) method in the gas phase and in various solvents. Solvent effects have been analyzed by using the self-consistent reaction field (SCRF) method based on polarizable continuum model (PCM) in chloroform, acetonitrile (ACN), dimethyl sulfoxide (DMSO), and water. Tautomers and conformations of the 3-atz molecule were also investigated. Energies, relative stabilities, and dipole moments of all conformers were compared and analyzed in the gas phase and in solvents as well. Raman spectrum was recorded only in solid state, infrared spectra were recorded in solid state as well in DMSO and in water solutions. In accordance with experimental results, our calculations showed that 3-atz1 is the most stable form in the gas phase and in solution. Geometrical parameters of 3-atz1 were slightly affected. Some harmonic wavenumbers, especially the NH and CH modes of 3-atz1 were noticeably affected by the choice of medium. Moreover, solvent effects on infrared and Raman intensities are quite considerable, and they increase as one goes from lower to higher dielectric constant.