Scaled quantum chemical studies of the structure and vibrational spectra of 2,4-diaminoquinazoline and 4-amino-2-methylquinoline

The solid phase FTIR and FT-Raman spectra of 2,4-diaminoquinazoline and 4-amino-2-methylquinoline have been recorded in the regions 4000-50 and 3500-100 cm−1, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculations based on density functional theory using standard B3LYP/6-31G* and B3LYP/6-311 + G** methods and basis set combinations and was scaled using various scale factors yielding fairly good agreement between observed and calculated frequencies. Based on the present good quality scaled quantum mechanical force field, a reliable description of the fundamentals was provided and the assignments have been proposed with the aid of normal coordinate analysis. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.