Quantum chemical density functional theory studies on the molecular structure and vibrational spectra of 4-amino-3-(4-chlorophenyl)- butanoic acid

Abstract

4-amino-3-(4-chlorophenyl)-butanoic acid(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 4ACBA 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 4ACBA were
obtained by the Restricted Hartree–Fock (RHF) and density functional theory (DFT) using 6-31G(d,p) basis set. The harmonic vibrational frequencies for 4ACBA were calculated 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 HF and (DFT/B3LYP) with 6-31G+(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 and chemical shift of the molecule were calculated using the gauge independent atomic orbital (GIAO) method.