Structural Effects in Solvolytic Reactions. 50. Steric Retardation in the Solvolysis of Tertiary Endo Bicyclic Derivatives. Evidence That the Exo:Endo Rate/Product Ratios for typical Reactions in Rigid U-Shaped Bicyclics Is a General Steric Phenomenon

Article abstract of DOI:10.1021/jo00212a036

The exo:endo rate ratios for the solvolysis in 80percent acetone at 25 deg C of the p-nitrobenzoates of tertiary bicyclic alcohols of widely varying U-shape character, such as 2-methyl- and 3-methyl-cis-bicyclo<3.3.0>octanols, 2-methyl-2-norbornanol, and 2-, 8-, and 9-methyl-endo-5,6-trimethylene-2-, -8-, and -9-norbornanols increase with increasing U-shape character of the bicyclic skeleton.This supports the proposal that steric retardation of ionization of the endo isomer is a major factor in governing the exo:endo rate ratios in these tertiary systems.A comparison of the solvolysis data with those of representative nonsolvolytic reactions in these U-shaped systems indicates that the exo/endo relative reactivities reveal a similar pattern for all of the reactions.The exo:endo ratios (product or rate) increase with increasing U-shape character of the bicyclic skeleton.Thus the large exo:endo rate ratio in the solvolysis of tertiary 2-norbornyl derivatives may as well be due to steric rather than to the long proposed electronic factor.