Theoretical and experimental investigation of (E)-2-([3,4-dimethylphenyl)imino]methyl)-3-methoxyphenol: Enol–keto tautomerism, spectroscopic properties, NLO, NBO and NPA analysis

The molecular structure and spectroscopic properties of (E)-2-([3,4-dimethylphenyl)imino]methyl)-3-methoxyphenol were investigated by X-ray diffraction, FT-IR and UV–vis spectroscopy. The vibrational frequencies calculatedusing DFT/B3LYP/6-31G(d,p) method. Results showed better agreement with the experimental values. The electronic properties was studied and the most prominent transition corresponds to π → π* and n → π*. Two types of intramolecular hydrogen bonds are strong OH⋯N interactions in enol-imine form and NH⋯O interactions in keto-amine form are compared by using density functional theory (DFT) method with B3LYP applying 6-31G(d,p) basis set. Both enol–keto tautomers engender six-membered ring due to intramolecular hydrogen bonded interactions. ry optimizations in solvent media were performed with the same level of theory by the polarizable continuum model (PCM). The effect of solvents on the tautomeric stability has been investigated. Stability of the molecule arises from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed using natural bond orbital (NBO) analysis. Molecular electrostatic potential (MEP) of the titled compound was studied for predicting the reactive sites. Mulliken population method and natural population analysis (NPA) have been studied. Population methods and MEP generally provides information regarding the chemical reactivity regions and charge distributions. Additionally, Frontier Molecular Orbitals analysis hasbeen performed from the optimized geometry. These orbitals also related to ionization potential, electron affinity, kinetic stability and hyperpolarizability of the molecule. The molecule exhibited good nonlinear optical (NLO) activity and first order hyperpolarizability. The predicted nonlinear optical properties of the title compound are 18 times greater than ones of urea.