Vibrational Spectroscopic Analysis of 4-amino-3-(4-chlorophenyl)-butanoic acid by Density Functional method

Abstract

4-amino-3-(4-chlorophenyl)-butanoicacid(4ACBA) otherwise commonly called as Baclofen is a drug used for the treatment of alcohol dependence The solid phase FT-IR and FT-Raman spectra of Baclofen were recorded in the regions 4000–400 cm_1 and 3500–100 cm_1 respectively. Theoretical vibrational frequencies , geometric parameters (bond lengths and bond angles),Thermodynamic properties,frequency and intensity of the vibrational bands , Natural population analysis and Mulliken atomic charges of Baclofen were obtained by the Restricted Hartree–Fock (RHF) density functional theory (DFT) with complete relaxation in the potential energy surface using 6-31G(d,p) basis set.The harmonic vibrational frequencies for Baclofen were calculated and the scaled values have been compared with experimental values of FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The electronic dipole moment (lD) and the first hyperpolarizability (βtot) values of the investigated molecule were computed using Density Functional Theory (DFT/B3LYP) and HF with 6-31+G(d,p) basis sets.The calculated results also show that the (4ACBA) molecule may have microscopy nonlinear optical (NLO) behavior with non zero values. 1H and 13C NMR spectra were recorded and1H and 13C nuclear magnetic resonance chemical shift of the molecule were calculated using
thegauge independent atomic orbital (GIAO) method.