Molecular structure, vibrational spectra, first order hyper polarizability, NBO and HOMO–LUMO analysis of 4-amino-3(4-chlorophenyl) butanoic acid

The Fourier transform infrared (FT-IR) and Fourier transform Raman (FTR) spectra of 4-amino-3(4-chlorophenyl) butanoic acid were recorded in the regions 4000–400 cm −1 and 4000–100 cm −1 , respectively, in the solid phase. Molecular electronic energy, geometrical structure, harmonic vibrational spectra, infrared intensities and Raman scattering activities, highest occupied molecular orbital, lowest unoccupied molecular orbital energy, energy gaps and thermodynamical properties such as zero-point vibrational energies, rotational constants, entropies and dipole moment were computed at the Hartree–Fock/6-31G(d,p) and three parameter hybrid functional Lee–Yang–Parr/6-31G(d,p) levels of theory. The vibrational studies were interpreted in terms of potential energy distribution (PED). The results were compared with experimental values with the help of scaling procedures. Most of the modes have wave numbers in the expected range and are in good agreement with computed values. The first order hyperpolarizability ( β total ) of this molecular system and related properties ( β , μ , 〈 α 〉 and Δ α ) are calculated using HF/6-31G(d,p) and B3LYP/6-31G(d,p) methods based on the finite-field approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond-like weak interaction has been analyzed using natural bond orbital (NBO) analysis by using B3LYP/6-31G(d,p) method. The results show that electron density (ED) in the σ ∗ and π∗ antibonding orbitals and second-order delocalization energies E (2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule.