Abstract: The regioselectivity of electrophilic aromatic substitution reactions in substituted arenes has traditionally been explained qualitatively through substituent electronic effects, yet quantitative analysis remains challenging. This study employs Natural Bond Orbital (NBO) analysis coupled with Frontier Molecular Orbital (FMO) theory to systematically examine charge distribution and reactivity in substituted arenes. By quantifying the influence of characteristic substituents (activating ortho/para-directing groups, deactivating ortho/para-directing groups, and meta-directing groups) on charge transfer within the aromatic ring, we elucidate the fundamental principles of electronic redistribution. Through visualization of electronic effects (NBO charge difference maps and electrostatic potential maps), we achieve quantitative interpretation of orientation rules in electrophilic aromatic substitution. This work presents a practical computational chemistry case study for organic chemistry education, enhancing students' understanding of regioselectivity and reactivity in aromatic electrophilic substitution reactions.

Key words: NBO analysis, Electrophilic substitution reaction, Orientation effect, Computational chemistry education