Density Functional Theory Investigation of Alkoxy-Substituted Pyrazolines: Structural, Electronic, and Thermodynamic Insights

https://doi.org/10.5281/zenodo.18835639

Abstract

A comprehensive density functional theory (DFT) investigation was conducted to evaluate the structural, electronic, and thermodynamic properties of alkoxy-substituted pyrazoline derivatives. Geometry optimization and frequency calculations were performed at the B3LYP/3-21G level of theory using Gaussian software. The optimized geometries revealed substituent-induced variations in bond lengths and bond angles, particularly around the C–F, N–N, and C–N bonds, confirming electronic redistribution within the heterocyclic framework. Frontier molecular orbital (FMO) analysis demonstrated that the HOMO is predominantly localized over the pyrazoline and aromatic core, while the LUMO extends toward electron-withdrawing substituents, indicating effective intramolecular charge transfer. The calculated HOMO–LUMO energy gaps suggest substituent-dependent modulation of chemical reactivity. Molecular electrostatic potential (MEP) maps identified electron-rich regions around oxygen and nitrogen atoms and electron-deficient sites near hydrogen and fluorinated carbons, highlighting potential reactive centers for electrophilic and nucleophilic interactions. Global reactivity descriptors, including hardness, softness, entropy, and Gibbs free energy, further confirmed the influence of alkoxy substitution on molecular stability and reactivity trends. Compounds with higher softness and smaller energy gaps exhibited enhanced electronic responsiveness. The combined theoretical analysis establishes a clear structure–property relationship and suggests that alkoxy-functionalized pyrazolines possess tunable electronic characteristics suitable for potential optoelectronic and pharmaceutical applications.