108-118The FTIR and FT-Raman spectra of 3-bromo-5-fluorobenzonitrile (BFBN) have been recorded in the regions 4000-400 cm-1 and 3500-400 cm-1, respectively. Utilizing the observed FT-Raman and FTIR data, a complete vibrational assignment and analysis of the fundamental modes of the compound have been carried out and subsequently confirmed by total energy distribution (TEDs). In the calculations performed to determine the optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, the density functional theory (DFT/B3LYP) method with 6-31+G(d,p) and 6-311++G(d,p) basis sets has been used. The results have been compared with the experimental values. The difference between the observed and scaled wavenumber values of most of the vibrational modes is very small. The NLO properties such as polarizability and first hyperpolarizability of the molecule have been calculated. The effects of frontier orbitals, HOMO and LUMO and the transition of electron density transfer have been discussed. The UV-Vis spectrum has been done which confirms the charge transfer of BFBN. The chemical interpretation of hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis
