A theoretical study of the nitration of ethylene and benzene with the nitronium ion

Abstract

Ab initio and semi-empirical (MNDO, MINDO/3) studies of the interaction of NO₂⁺ with ethylene and benzene are reported. 6-31G**//4-31G Calculations have been performed at selected points of the ethylene–nitrnium ion energy hypersurface, as well as RMP2 4-31G//4-31 G calculations, from which it is found that the non-classical π-complex is more stable than the classical nitro complex. Fully optimised STO-3G calculations are described for 5 stationary points of the benzene–NO₂⁺ hypersurface; 3-21G calculations at these geometries show that the nitrito σ-complex and a 5-membered-ring structure have similar energies. 4-31G//STO-3G Calculations however show the nitro from to be the next most stable to the nitrito form. Geometry optimisation at the 3-21G level of the nitrito and nitro forms shows this finding to persist at both the 3-21G and 4-31G levels. If correlation is introduced via GVB/1 calculations both nitro compounds are shown to possess incipient biradicaloid character. Finally semi-empirical MINDO/3-solvaton calculations of solvation effects show that the nitro form is the most stabilised in both systems.