Substituent Effects of -NO and -NO₂ Groups in Aromatic Systems

The nitro and nitroso derivatives of methane, benzene, and Li-phenolate weee theoretically investigated with the help of quantum chemical methods (SCF, MP2). Experimental densities weee examined with the OIAM approach. MP2 geometries weee in excellent agreement with advanced experimental data. Geometries, electron densities, atomic charges, and atomic shapes, bond orders, torsional barriers, and reaction energies were analyzed in order to elucidate the inductive and mesomeric influence of NO in comparison to NO₂. These influences behave partly additive with -I(NO) < -I(NO₂), partly nonlinear and nonadditive with -M(NO₂) < -M(NO). Despite some π-character of the PhNO₂ bond, the mesomeric influence of NO₂ on a nonsubstituted benzene ring is very small, but becomes enhanced by para-donors or corresponding intermolecular interactions.