A multi‐descriptor analysis of substituent effects on the structure and aromaticity of benzene derivatives: π‐Conjugation versus charge effects

Abstract

This work provides a detailed multi‐component analysis of aromaticity in monosubstituted (X = CH₃, C, C, NH₂, NH⁻, NH⁺, OH, O⁻, and O⁺) and para‐homodisubstituted (X = CH₃, CH₂, NH₂, NH, OH, and O) benzene derivatives. We investigate the effects of substituents using single‐reference (B3LYP/DFT) and multireference (CASSCF/MRCI) methods, focusing on structural (HOMA), vibrational (AI(vib)), topological (ELF_π), electronic (MCI), magnetic (NICS), and stability (S₀–T₁ splitting) properties. The findings reveal that appropriate π‐electron‐donating and π‐electron‐accepting substituents with suitable size and symmetry can interact with the π‐system of the ring, significantly influencing π‐electron delocalization. While the charge factor has a minimal impact on π‐electron delocalization, the presence of a p_z orbital capable of interacting with the π‐electron delocalization is the primary factor leading to a deviation from the typical aromaticity characteristics observed in benzene.