Vibrational spectroscopy investigation and HOMO, LUMO analysis using DFT (B3LYP) on the structure of 1,3-dichloro 5-nitrobenzene

Vibrational spectral measurements, namely, FT-infrared (4000–400 cm−1) and FT-Raman (3500–50 cm−1) spectra have been made for 1,3-dichloro 5-nitrobenzene (DCNB) and assigned to different normal modes of the molecule. Optimized geometrical structure, harmonic vibrational frequencies, intensities, Mulliken's net charges and several thermodynamic parameters in the ground state have been computed by the B3LYP, density functional method using 6-311+G(d,p),6-311++G(d,p) basis sets. Complete assignments of the observed spectra have been proposed. Most of the modes have wave numbers in the expected range. Coupling of vibrations has been determined by calculating total energy distributions (TED) with the help of specific scaling procedures. The calculated HOMO and LUMO energies and electrostatic potential shows that charge transfer occurs within the molecule. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound which showed excellent agreement with the observed spectra.

Graphical abstract. Vibrational spectral measurements, namely, FT-infrared (4000–400 cm−1) and FT-Raman (3500–50 cm−1) spectra have been made for 1,3-dichloro 5-nitrobenzene (DCNB) and assigned to different normal modes of the molecule. Optimized geometrical structure, harmonic vibrational frequencies, intensities, Mulliken's net charges and several thermodynamic parameters in the ground state have been computed by the B3LYP, density functional method using 6-311+G(d,p),6-311++G(d,p) basis sets. Complete assignments of the observed spectra have been proposed. Most of the modes have wave numbers in the expected range. Coupling of vibrations has been determined by calculating total energy distributions (TED) with the help of specific scaling procedures. The calculated HOMO and LUMO energies and electrostatic potential shows that charge transfer occurs within the molecule. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound which showed excellent agreement with the observed spectra.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights• Influence of NO2 group and the electron withdrawing nature of chlorine atom discussed using Mulliken's charges. • HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. • Electrostatic potential surface provides a visual representation of the chemically active sites and comparative reactivity of atoms.