The spectroscopic (FTIR, FT-Raman, UV and NMR), first-order hyperpolarizability and HOMO–LUMO analysis of 4-amino-5-chloro-2-methoxybenzoic acid

The solid phase FTIR and FT–Raman spectra of 4-amino-5-chloro-2-methoxybenzoic acid (4A5Cl2MBA) have been recorded in the regions 400–4000 and 50–4000 cm–1, respectively. The spectra have been interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule has been optimized and the structural characteristics have been determined by density functional theory (B3LYP) method with 6-311++G(d,p) as basis set. The vibrational frequencies were calculated for most stable conformer and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra have also been predicted from the calculated intensities. 1H and 13C NMR spectra were recorded and 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV–Visible spectrum of the compound was recorded in the region 200–400 nm and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. Nonlinear optical and thermodynamic properties were interpreted. All the calculated results were compared with the available experimental data of the title molecule.