DFT computations and spectroscopic analysis of p-bromoacetanilide

• FT-IR and FT-Raman spectra of PBA in solid phase were recorded and analyzed.
• The vibrational wavenumbers were computed using B3LYP/6-311++G(d,p) and MPW1PW91/6-311++G(d,p) basis set method.
• The vibrational assignment and spectroscopic analysis have been carried out.
• The NBO/NLMO analysis explained the intramolecular hydrogen bonding.

This work presents the characterization of p-bromoacetanilide (PBA) by quantum chemical calculations and spectral techniques. The spectroscopic properties were investigated by FT-IR, FT-Raman and UV–Vis techniques. The structural and spectroscopic data of the molecule were obtained from B3LYP/6-311++ G(d,p) and MPW1PW91/6-311++G(d,p) basis set calculations. The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the normal co-ordinate analysis (NCA), experimental results and potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method, interpreted in terms of fundamental modes. The stability of molecule has been analyzed by NBO/NLMO analysis. The molecular orbital contributions were studied by using the density of states. The electronic properties like UV–Vis spectral analysis and HOMO–LUMO energies were reported. The calculated HOMO and LUMO energies shows that charge transfer interactions taking place within the molecule. Mulliken population analysis on atomic charges, Statistical thermodynamic properties at various temperatures of the PBA is also calculated.

A complete vibrational analysis of PBA is performed by combining the experimental and theoretical information using Pulay’s density functional theory (DFT) based on scaled quantum chemical approach. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.Figure optionsDownload as PowerPoint slide