SUBSTITUENT EFFECTS OF -NO AND -NO2 GROUPS IN AROMATIC SYSTEMS

The nitro and nitroso derivatives of methane, benzene, and Li-phenolate were theoretically investigated with the help of quantum chemical methods (SCF, MP2). Experimental densities were examined with the OIAM approach. MP2 geometries were 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 pi-character of the PhNO(2) bond, the mesomeric influence of NO2 on a nonsubstituted benzene ring is very small, but becomes enhanced by para-donors or corresponding intermolecular interactions.