Electronic effects of the functional groups in ortho-Nitrobenzenesulfonic acids on the results of NBO analysis

An NBO analysis of electronic density distribution is performed for gaseous benzenesulfonic acid and its mono- and trinitro-substituted molecules (B3LYP, MP2, HF /cc-pVTZ). The energy of orbital inter-actions of nitro and sulfonic groups with benzene ring orbitals is calculated for the most stable acid conformers, and the contributions of inductive and resonance effects of substituents are determined. The dependences of these contributions on the positions and number of nitro groups in an aromatic ring and the possibility of intramolecular hydrogen bond formation are revealed. The nitro group in nitrobenzene exhibits a stronger electron-acceptor effect than the sulfonic group in benzenesulfonic acid. Under the influence of the strong electron-acceptor properties of the nitrogroups, the sulfonic group has a donating effect in ortho-nitrosubstituted benzenesulfonic acids.