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

The nitro and nitroso derivatives of methane, benzene, and Li-phenolat e were theoretically investigated with the help of quantum chemical me thods (SCF, MP2). Experimental densities were examined with the OIAM a pproach. MP2 geometries were in excellent agreement with advanced expe rimental data. Geometries, electron densities, atomic charges, and ato mic shapes, bond orders, torsional barriers, and reaction energies wer e analyzed in order to elucidate the inductive and mesomeric influence of NO in comparison to NO2. These influences behave partly additive w ith -I(NO) < -I(NO2), partly nonlinear and nonadditive with -M(NO2) < -M(NO). Despite some pi-character of the PhNO(2) bond, the mesomeric i nfluence of NO2 on a nonsubstituted benzene ring is very small, but be comes enhanced by para-donors or corresponding intermolecular interact ions.