Computational Studies on Keto-Enol Tautomerism of Mesoxaldehyde, 1,2-Bis-Phenyl Hydrazone (MBPH) in the Gas Phase Using HF and DFT Methods, to Investigate the Possibility of Using This Structure for the Synthesis of Different Heterocyclic Compounds, Confirmed by Spectral Tools

In this article, the optimized geometries of six possible tautomers of mesoxaldehyde 2,3-bis-phenyl hydrazone (MBPH) (1) have been studied in the gas phase by ab initio Hartree-Fock (HF) and density Functional theories DFT with different levels of theory, B3LYP, B3PW91, WB97XD, with 6-311G(d,p) basis set. The different conformers of the compound were studied using the B3LYP functional with a 6-311G(d,p) basis set. Optimum molecular geometries, electronic properties, and energetics of these systems have been discussed as the energy gap was determined using HOMO and LUMO energy values. Also, the reactivity descriptors such as Hardness (η), Softness (1/η), electronegativity index (χ), Chemical potential (μ), Electrophilicity (ω = 𝜇2/2𝜂), and Nucleophilicity (EHOMO + 9.12), indicate the electrophilic and nucleophilic nature of the different tautomers. The most stable conformer with the minimum energy was identified. This conformer was used for further computations, and electrophilic and nucleophilic regions have been identified with the aid of an MESP plot. The contour map shows electron density flow in the molecule. Thermodynamic properties and tautomeric equilibria between different tautomers were calculated using frequency calculations. Finally, mesoxaldehyde is used as a starting material to synthesize new heterocycles identified by different spectral tools.