FT-IR, FT-Raman, ab initio, HF and DFT studies, NBO, HOMO–LUMO and electronic structure calculations on 4-chloro-3-nitrotoluene

In this work, the vibrational spectral analysis was carried out by using Raman and infrared spectroscopy in the range 100–4000 cm−1 and 50–4000 cm−1, respectively, for 4-chloro-3-nitrotoluene (C7H6NO2Cl) molecule. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on Hartree Fock (HF) and density functional theory (DFT) method and different basis sets combination. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other methods. The calculated HOMO and LUMO energies shows that charge transfer within the molecule. The effects due to the substitutions of methyl group, nitro group and halogen were investigated. The results of the calculations were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) and thermodynamic properties were performed.

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► Molecular structure of 4-chloro-3-nitrotoluene molecule was studied using HF and DFT/B3LYP.
► All results were compared with experimental (FT-IR and FT-Raman) spectra.
► Molecular electrostatic potential (MEP) and HOMO–LUMO energies of 4-chloro-3-nitrotoluene was calculated.
► Thermodynamic properties (heat capacity, entropy and enthalpy) of 4-chloro-3-nitrotoluene were performed.