Density functional theory studies on tautomeric stability and infrared and Raman spectra of some purine derivatives

The molecular vibrations of 6-hydroxy-purine (6HP) and 6-amino-purine (6AP) were investigated in polycrystalline sample, at room temperature by Fourier transform infrared (FTIR) and FT-Raman spectroscopy. The spectra of the above compounds have been recorded in the region 4000-50, 3500-100 cm−1, respectively. They were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculations based on density functional theory (DFT) using HF/6-31G* and B3LYP/6-311+G** methods and basis set combinations. The results of the calculations were applied to simulated infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. The dipole moment and the tautometric stability of purine derivatives were also studied.