Quantum mechanical study and spectroscopic (FT-IR, FT-Raman, 13C, 1H) study, first order hyperpolarizability, NBO analysis, HOMO and LUMO analysis of 2-acetoxybenzoic acid by density functional methods

• The FT-IR, FT-Raman, NMR spectral investigation of title molecule has been performed using DFT methods.
• Optimized parameters were calculated.
• The complete assignments are performed on the basis of the potential energy distribution (PED).
• The redistribution of electron density has been discussed.
• Hyperpolarizability, HOMO and LUMO energies were calculated.

In this work, colorless crystals of 2-acetoxybenzoic acid were grown by slow evaporation method and the FT-IR and FT-Raman spectra of the sample were recorded in the region 4000–500 cm−1 and 4000–100 cm−1 respectively. Molecular structure is optimized with the help of density functional theory method (B3LYP) with 6-31+G(d,p), 6-311++G(d,p) basis sets. Stability of the molecule arising from hyperconjugation and charge delocalization is confirmed by the natural bond orbital analysis (NBO). The results show that electron density (ED) in the σ∗ antibonding orbitals and E(2) energies confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis following the scaled quantum mechanical force field (SQMFF) methodology. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO method. Mulliken population analysis on atomic charges is also calculated. The calculated HOMO and LUMO energy gap shows that charge transfer occurs within the molecule.

The Fourier transform infrared and Raman spectra of 2-acetoxy benzoic acid are recorded in solid phase, the harmonic vibrational frequencies, infrared intensities, Raman activities, bond length, bond angle are calculated by DFT methods using 6-31+G(d,p), 6-311++G(d,p) basis sets. The observed and calculated frequencies showed very good agreement with experimental values. HOMO and LUMO energies are calculated that these energies show charge transfer occurs within the molecule. Thermodynamic properties were calculated.Figure optionsDownload as PowerPoint slide