Comparative quantum-chemical investigation of 2-chloro-N-(4-methoxyphenyl)acetamide and 2-(4-methoxyphenylamino)-2-oxoethyl meth/acrylate: DFT, TD-DFT, and non-covalent interaction analyses

In this study, a comparative quantum-chemical investigation of 2-chloro-N-(4-methoxyphenyl)acetamide (p-acetamide), 2-(4-methoxyphenylamino)-2-oxoethyl acrylate (MPAEA), and 2-(4-methoxyphenylamino)-2-oxoethyl methacrylate (MPAEMA) was carried out to elucidate the effects of progressive structural modification on their electronic, spectroscopic, thermochemical, and non-covalent interaction properties. Geometry optimizations and electronic-structure calculations were performed within the framework of density functional theory using the 6-311G basis set. Electronic properties were analyzed through natural bond orbital (NBO) analysis, frontier molecular orbital (FMO) distributions, and global reactivity descriptors. The calculated HOMO-LUMO energy gaps revealed that MPAEA exhibits enhanced charge-transfer capability because of its conjugated acrylate structure, whereas MPAEMA shows a larger gap, suggesting higher electronic stability. Time-dependent density functional theory (TD-DFT) calculations were used to predict UV-Vis absorption features, revealing that structural modification significantly influences excitation energies and optical responses. Molecular electrostatic potential (MEP) maps and density of states (DOS/tDOS) analyses provided further insight into charge distribution and orbital contributions, highlighting increased electron delocalization in conjugated systems. Thermochemical analysis showed that thermal energy, heat capacity, and entropy increased systematically with temperature for all molecules, with MPAEMA exhibiting the highest thermodynamic values because of its extended molecular framework. Non-covalent interaction (NCI), density overlap regions indicator (DORI), and reduced density gradient (RDG) analyses revealed distinct weak-interaction patterns, confirming that structural complexity enhances interaction diversity and electron-density distribution. Overall, the results indicate that the transformation from the acetamide framework to acrylate and methacrylate derivatives significantly modifies the electronic structure, optical behavior, thermodynamic response, and interaction topology of methoxyphenyl-based molecular systems.