FT-IR and FT-Raman spectra, MEP and HOMO–LUMO of 2,5-dichlorobenzonitrile: DFT study

• The Raman and IR spectra of 2,5-dichlorobenzonitrile were accurately simulated.
• M052X and M06L DFT methods appear to underestimate the CC bond lengths.
• M052X and M06L/6-31G** scaled wavenumbers are slightly worse than by B3LYP.
• An accurate scaling procedure was used to improve the calculated wavenumbers.
• The energy gap HOMO–LUMO reflects the chemical activity of the molecule.

The experimental FT-IR and FT-Raman spectra of 2,5-dichlorobenzonitrile molecule were recorded at room temperature, and the results compared with quantum chemical theoretical values using MP2 and DFT methods. Molecular geometry, vibrational wavenumbers and thermodynamic parameters were calculated. With the help of specific scaling procedures for the computed wavenumbers, the experimentally observed FTIR and FT-Raman bands were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range and the error obtained was in general very low. Several general conclusions were deduced. The NBO analysis has been done and Molecular Electrostatic Potential (MEP) has been plotted.

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