Steric vs. Stereoelectronic Effects in Carbocation Reactions of the 2-Bicyclononyl System

Article abstract of DOI:10.1021/jo00157a009

An investigation of anti-9-methyl substituent effects upon the kinetics and products of hydrolysis of the cis-ring-fused endo- and exo-2-bicyclo<6.1.0>nonyl 3,5-dinitrobenzoates in 80percent aqueous acetone has been carried out.In the exo system, the anti-9-methyl substituent produced only a small rate-accelerating effect of 1.8 at 80 deg C.However, for the endo system acceleration by a factor of 4.7 was observed.In neither system did the anti-9-methyl substituent affect the exo:endo product ratio.With the anti-6-methyl-2-bicyclo<3.1.0>hexyl 3,5-dinitrobenzoates, which were studied for comparison, the anti-6-methyl substituent exhibited an identical rate-accelerating effect of 8.3 in both the endo and the exo isomers.Also, with both isomers an identical exo:endo product ratio was observed.On the basis of these results, it is proposed that the stereoselectivities observed in product formation in the 2-bicyclo<6.1.0>nonyl system are not due primarily to electronic factors but result mainly from steric effects upon structurally different, noninterconverting intermediates with bisected delocalization.