Molecular structure, vibrational spectroscopic and HOMO, LUMO studies of 4-nitroaniline by density functional method

Quantum mechanical calculations of energies, geometries and vibrational wavenumbers of 4-nitroaniline (4NA) were carried out by using Density functional theory (DFT /B3LYP/6-311++G(d,p)/ CC-pvdz / Aug-cc-Pvdz) method. The optimized geometrical parameters obtained by B3LYP method show good agreement with experimental X-ray data. The best level of theory in order to reproduce the experimental wavenumbers is B3LYP method with the 6-311++G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared spectra of 4NA was also reported. The calculated HOMO and LUMO energies show that charge transfer occurs in the molecule. The theoretical spectrogram for FTIR and FT-Raman spectra of the title molecule have been constructed.