Theoretical study of the reactions of breaking of the intramolecular H-bonds in 4-(3,4-dihydroxyphenyl)-7,8-dihydroxy-2H-1-benzopyran-2-one and the reactivity indexes of the compound and its derivatives

Abstract

Coumarin derivatives exhibit diverse structural features and electronic behaviors that directly influence their biological activity and chemical reactivity. Understanding how aryl substitution and hydroxyl-group methylation alter frontier orbital energies and global reactivity descriptors is essential for predicting their interaction tendencies and potential biofunctions. Despite extensive experimental studies, a systematic theoretical comparison of these structural variants remains limited, highlighting the need for a detailed DFT-based evaluation. A series of coumarin derivatives were investigated using Density Functional Theory at the B3LYP/6-311G(d,p) level in the gas phase. Geometry optimizations and vibrational analyses were performed to confirm true minima. Frontier molecular orbital energies, ionization potential, electron affinity, electronegativity, chemical hardness/softness, electrophilicity index, and maximum charge-transfer capacity were calculated using Koopmans-based relationships and standard conceptual DFT formalisms. Structural features such as planarity, intramolecular hydrogen bonding, and substituent-induced torsion were correlated with electronic and reactive properties. Comparative analysis was performed to elucidate the influence of structural modifications on electronic behavior.