QUANTUM CHEMICAL INVESTIGATION OF 1-(2-THENOYL)-3,3,3-TRIFLUOROACETONE BENZOYLHYDRAZONE: OPTIMIZED GEOMETRY, ELECTRONIC STRUCTURE, FRONTIER MOLECULAR ORBITALS, AND VIBRATIONAL ANALYSIS AT THE DFT/B3LYP LEVEL

The molecular geometry, electronic structure, frontier molecular orbitals, Mulliken charge distribution, vibrational spectrum, and global chemical reactivity descriptors of 1-(2-thenoyl)-3,3,3-trifluoroacetone benzoylhydrazone (L1, C₁₅H₁₁F₃N₂O₂S) were investigated computationally at the B3LYP/6-311G(d,p) level of density functional theory using the Gaussian 16 program package. Full geometry optimization was carried out without symmetry constraints, and the nature of the stationary point was verified by harmonic frequency analysis. The optimized structure reveals characteristic bond lengths for the key functional groups: the hydrazone C=N bond (1.279 Å), the thenoyl C=O bond (1.216 Å), the amide C=O bond (1.208 Å), and the C–F bond lengths of the CF₃ group (1.339–1.363 Å). The HOMO and LUMO energies are −6.196 and −2.486 eV, respectively, giving a HOMO–LUMO gap of 3.710 eV. Global reactivity descriptors derived from frontier orbital theory indicate that L1 is a moderately hard electrophile with an electrophilicity index ω = 5.080 eV. The HOMO is delocalized over the entire π-conjugated framework, while the LUMO is concentrated on the CF₃-bearing hydrazone segment. Computed IR-active bands at 1792 and 1735 cm⁻¹ are assigned to the thenoyl and benzoyl C=O stretching modes, respectively, and the N–H stretching appears at 3547 cm⁻¹. Standard thermochemical properties at 298.15 K are also reported. The results establish a reliable structural and electronic reference for L1 and provide a foundation for modeling its coordination chemistry and biological activity.