FT-IR, FT-Raman spectra, NBO, HOMO-LUMO and thermodynamic functions of 4-chloro-3-nitrobenzaldehyde based on ab initio HF and DFT calculations.

FT-IR (4000-400 cm(-1)) and FT-Raman (3500-100 cm(-1)) spectral measurements of 4-chloro-3-nitrobenzaldehyde have been done. Ab initio (HF/6-311+G(d,p)) and DFT (B3LYP/6-311+G(d,p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, infrared intensities and Raman activities. A detailed interpretation of the FT-IR and FT-Raman spectra of 4-chloro-3-nitrobenzaldehyde are reported on the basis of the calculated potential energy distribution. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The HOMO and LUMO energy gap reveals that the energy gap reflects the chemical activity of the molecule. The thermodynamic functions of the title compound have been performed by HF/6-311+G(d,p) and B3LYP/6-311+G(d,p). The observed and calculated wave numbers are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed spectra. Thermodynamic functions were calculated using vibrational wave numbers for different temperatures.