Molecular structure, spectroscopic (FT-IR, FT-Raman) studies and first-order molecular hyperpolarizabilities, HOMO–LUMO, NBO analysis of 2-hydroxy-p-toluic acid

FT-Raman and FT-IR spectra for 2-hydroxy-p-toluic acid molecule had been recorded in the regions 3500–100 cm−1 and 4000–400 cm−1, respectively. Vibrational frequencies have been calculated in optimum state by employing density functional theory (DFT) and Hartree Fock (HF) methods with 6-311++G(d,p) basis set in monomeric form. SQM force fields have also been used to calculate potential energy distributions in order to make conspicuous vibrational assignments. Optimized geometries of the molecule had been interpreted and compared. The electric dipole moment and first hyperpolarizability values of the investigated molecule were computed using ab initio and DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond analysis. The results show that charge in electron density (ED) in the σ* antibonding orbitals and E(2) energies confirms the occurrence of ICT within the molecule.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Spectral investigation of 2-hydroxy-p-toluic acid performed using HF and DFT methods. ► The dimerized system is well demonstrated by the red shift in OH stretching frequency. ► Mullikan’s net charges have been calculated and compared with natural atomic charges. ► Stability, charge delocalization analyzed by using NBO theory. ► Molecular interactions on monomer and dimer structures of HTA were reported.