FTIR and FT-Raman spectra, molecular geometry, vibrational assignments, first-order hyperpolarizability, ab initio and DFT calculations for 3,4-dimethoxybenzonitrile

Quantum chemical calculations of energies, geometrical structure and vibrational wave numbers of 3,4-dimethoxybenzonitrile (DMBN) were carried out by the ab initio Hartree–Fock (HF) and density functional theory (DFT) with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. Making use of the recorded data, the complete vibrational assignments are made and analysis of the observed fundamental bands of molecule is carried out. The geometries and normal modes of vibrations obtained from ab initio HF and B3LYP calculations are in good agreement with the experimentally observed data. The electric dipole moment (μ) and the first hyperpolarizability (β) values of the investigated molecule have been computed using ab initio quantum mechanical calculations. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. The theoretical FTIR and FT-Raman spectra for the title molecule have been constructed.

Quantum chemical calculations of energies, geometrical structure and vibrational wave numbers of DMBN were carried out by the ab initio Hartree–Fock (HF) and density functional theory (DFT) with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. Making use of the recorded data, the complete vibrational assignments are made and analysis of the observed fundamental bands of molecule is carried out. The electric dipole moment (μ) and the first hyperpolarizability (β) values of the investigated molecule have been computed using ab initio quantum mechanical calculations. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. The theoretical FTIR and FT-Raman spectra for the title molecule have been constructed.Figure optionsDownload as PowerPoint slideHighlights
• Vibrational wave numbers, electric dipole moment and first hyperpolarizability of 3,4-dimethoxybenzonitrile were carried out.
• Computed geometrical parameters are in good agreement with X-ray diffraction data.
• Potential energy surface scan with the B3LYP/6-311++G(d,p) level of theoretical approximations was performed.
• The experimental wave numbers are compared with the results of DFT and ab initio calculations.
• HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule.