Journal of Chemical and Pharmaceutical Research (ISSN : 0975-7384)

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Original Articles: 2011 Vol: 3 Issue: 5

Molecular structure, spectroscopic (FT-IR, FT-Raman, NMR) studies and first-order molecular hyperpolarizabilities of 5-amino-2-hydroxybenzoic acid (5A2HBA) by ab initio HF and density functional method

Abstract

The Fourier transform infrared (FT-IR) and FT Raman spectra of 5-amino-2-hydroxybenzoic acid (5A2HBA) have been recorded in the regions 4000–400 and 4000–100 cm−1, respectively. 5-amino-2-hydroxybenzoic acid is used as an anti-inflammatory agent .The optimized geometry, frequency and intensity of the vibrational bands of (5A2HBA) were obtained by ab initio and DFT levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) basis set. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. The harmonic vibrational frequencies, infrared intensities and Raman scattering activities, force constants are calculated by ab initio HF and DFT B3LYP methods with 6-31G(d,p) basis set. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the σ* and p* anti bonding orbitals and E2 energies confirms the occurrence of ICT (Intra molecular Charge Transfer) within the molecule. 13C and 1H NMR chemical shifts results were given and are in agreement with the corresponding experimental values. Highest occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) energy gaps were studied. The scaled theoretical wavenumbers show good agreement with the experimental values. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.