Orbital interactions. IX. The effect of remote substituents on the electrophilic nitration of a series of 11-substituted exo-hexahydro-7,10-methanofluoranthenes

Abstract

Product distribution and the relative rates of nitration (Cu(NO3)2,3H2O/Ac₂O) of a series of 11-substituted exo-hexahydro-7,10- methanofluoranthenes, (8), (9b), (10) and (11b), and acenaphthene, (12), have been determined. It was observed that a syn-methoxy substituent, as in (11b), greatly enhanced the reactivity of the acenaphthene ring towards nitration compared with unsubstituted (8), the α position being activated more than the γ position. Precisely the opposite result was obtained for the nitration of the ketone (10). These results are explained in terms of the consequences of through- space orbital interactions (OITS), operating between the molecular orbitals of the 11-substituent and those of the acenaphthene ring; a PMO model is used for the nitration reaction. The results of INDO MO SCF calculations on the water-acenaphthene complex (22) and the formaldehyde-acenaphthene complex (23), which are intended to mimic the salient features of (11b) and (10) respectively, lend support to the OITS proposal. However, alternative proposals, based on field effects (in the case of (10)) and on the formation of a complex (24) for the nitration of (11b), are also discussed.