Spectroscopic (FT-IR and FT-Raman) investigation, first order hyperpolarizability, NBO, HOMO–LUMO and MEP analysis of 6-nitrochromone by ab initio and density functional theory calculations

• The optimized geometries and harmonic vibrational wavenumbers of 6-nitrochromone have been carried out.
• The vibrational frequencies were calculated by HF and DFT methods and are discussed.
• Stability of the molecule arising from hyperconjugative interactions have been analyzed using NBO analysis.
• Mulliken’s charges, HOMO–LUMO, MEP analysis and several thermodynamic properties were performed.

The vibrational spectral analysis is carried out using FT-Raman and FT-IR spectroscopy in the range 3500–50 cm−1 and 4000–400 cm−1, respectively, for 6-nitrochromone (6NC). The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimization and normal coordinates force field calculation based on ab initio HF and DFT gradient calculations employing the HF/6-311++G(d,p) and B3LYP/6-311++G(d,p) basis set. Stability of the molecule has been analyzed using NBO analysis. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Thermodynamic properties like entropy, heat capacity, zero-point energy and Mulliken’s charge analysis have been calculated for the 6NC. The complete assignments were performed on the basis of total energy distribution (TED) of the vibrational modes with scaled quantum mechanical (SQM) method. The MEP map shows the negative potential sites are on oxygen atoms as well as the positive potential sites are around the hydrogen atoms.

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