Kosar, Basak2025-03-232025-03-2320110219-63361793-6888https://doi.org/10.1142/S021963361100644Xhttps://hdl.handle.net/11486/5199This work presents a computational study on the tautomeric forms of (E)-4-Methoxy-2[(4-nitrophenyl)iminomethyl]phenol, an ortho-hydroxy Schiff base compound. The electronic structure of title compound has been characterized at the B3LYP/6-311G(d,p) level of density functional theory. The first hyperpolarizability values have been obtained from the molecular polarizabilities for both tautomers. The second-order non-linear optical properties have been investigated based on their relationships with the natural bond orbitals and frontier molecular orbitals. The changes of thermodynamic properties with temperature going from 100 K to 300 K have been investigated for the reactants and the reaction products tautomers. Tautomeric equilibrium constant derived from the difference between the Gibbs free energies of tautomers has been obtained at different temperatures. The relationship between formation enthalpy and entropy changes has been investigated with the enthalpy-entropy compensation.eninfo:eu-repo/semantics/closedAccessSecond-order non-linear optical propertiesnatural bond orbital analysisthermodynamic functionsdensity functional theorySchiff baseArticle10327929510.1142/S021963361100644X2-s2.0-79957565659N/AWOS:000293397000002N/A