Amide imidic prototropic tautomerization of efavirenz, NBO analysis, hyperpolarizability, polarizability and HOMO–LUMO calculations using density functional theory

ensity functional theory (DFT) was performed in the gas phase to investigate the tautomerization and transi?tions in efavirenz. The amide and imidic tautomers’ geometrical parameters are performed using B3LYP/6- 31++G** and M06-2X/ cc-pVTZ (-F). The results showed that the amide tautomer is more stable than the imidic tautomer in the gas phase. The non-linear optical (NLO) properties of the amide and imidic tautomers are computed. Interestingly, the amide and imidic forms may be an attractive compound in enhancing NLO con?stituents due to their valuable non-linear property. Natural bond orbital (NBO) analyses have been performed on the amide and imidic tautomers. The substantial differences in occupancies and the energies of bonding and anti?bonding orbital have been analyzed and described. Notably, thermodynamic (Gibbs free energy, entropy, and enthalpy) properties of proton intra-migration of the tautomers via a single proton shift in the gas phase were predicted. The detailed results revealed that the kinetic and thermodynamic favorability increased from imidic tautomer to amide, hence the pathway to the amide arrangement of efavirenz is a favorable reaction. Besides this, the electrostatic potential surface plots have been used to explore the possible site for electron-withdrawing and donating. The frontier molecular orbital reveals the energy gap and chemical activity of the tautomers.