Vibrational spectroscopic (FT-IR and FT-Raman), first-order hyperpolarizablity, HOMO, LUMO, NBO, Mulliken charges and structure determination of 2-bromo-4-chlorotoluene

The FT-IR and FT-Raman spectra of 2-bromo-4-chlorotoluene (2B4CT) molecule have been recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1), respectively. Optimized geometrical structures, harmonic vibrational frequencies, intensities, reduced mass, force constants and depolarization ratio have been computed by the B3 based (B3LYP) density functional methods using 6-31+G(d,p) and 6-311++G(d,p) basis sets. The observed FT-IR and FT-Raman vibrational frequencies are analysed and compared with theoretically predicted vibrational frequencies. The geometries and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The Mulliken charges, the natural bonding orbital (NBO) analysis, the values of electric dipole moment (μ) and the first-order hyperpolarizability (β) of the investigated molecule were computed using DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The influences of bromine atom, chlorine atom and methyl group on the geometry of benzene and its normal modes of vibrations have also been discussed.