Structural study and vibrational spectra of 3-amino-2-(4-chlorophenyl) quinazolin-4(3H)-one

We have carried out a structural and vibrational study for 3-amino-2-(4-chlorophenyl) quinazolin-4(3H)-one by using the available experimental infrared spectrum and theoretical calculations based the density functional theory (DFT). The structural properties for the compound, such as the bonds order, charge-transfers and topological properties were studied by means of the Natural Bond Orbital (NBO) and the Atoms in Molecules theory (AIM) investigation. The harmonic vibrational wavenumbers for the optimized geometry were calculated at B3LYP/6-31G* and B3LYP/6-311++G** levels. For a complete assignment of the compound infrared spectrum, the DFT calculations were combined with Pulay’s scaled quantum mechanical force field (SQMFF) methodology in order to fit the theoretical wavenumbers values to the experimental ones. The results were then used to predict the Raman spectra, for which there are no experimental data. An agreement between theoretical and available experimental results was found and a complete assignment of all the observed bands in the vibrational spectra was performed. The theoretical vibrational calculations allowed us to obtain a set of scaled force constants fitting the observed wavenumbers. Additionally, the frontier molecular HOMO and LUMO orbitals for the compound were analyzed and compared with those calculated for the 3-amino-2-phenyl quinazolin-4(3H)-one molecule.