Collect. Czech. Chem. Commun. 1999, 64, 1849-1876

The Nature and Transmission of Substituent Electrical Effects in Alicyclic Solvolysis

Marvin Charton

Chemistry Department, School of Liberal Arts and Science, Pratt Institute, Brooklyn, NY 11201, U.S.A.


The correlation of rate constants taken from the literature for 2-exo- and 2-endo-norbornyl derivatives substituted in positions 1, 4, 5-exo, 6-exo, 6-endo, and 7-anti with the triparametric LDR equation and relationships derived from it has been carried out. A delocalized (resonance) electrical effect has been found in all but the 4-substituted derivatives. The resonance effect may be somewhat greater when the leaving group is exo than when it is endo. Steric effects occur in the 6-endo-substituted derivatives. The transition state resembles a classical carbocation rather than the nonclassical norbornyl carbocation. The correlation of solvolysis rate constants for 2- and 3-substituted 1- and 4-exo-substituted 2-exo-adamantyl derivatives gave no reliable indication that a delocalized electrical effect existed in these systems. A study of solvolysis rate constants for 4-substituted 1-[2.2.2]bicyclooctanyl, 6-exo-substituted [2.2.2]bicyclooctan-2-exo-yl and 6-exo-substituted [2.2.2]bicyclo- octan-2-endo-yl derivatives showed a delocalized electrical effect only in the latter of these systems. Such an effect was also observed in 4-substituted 2-chloro-2-methylbutane solvolyses. The transmission of electrical effects is by a modified field effect. It is dependent on 1/n where n is the number of bonds intervening between substituent and reaction site.

Keywords: Substituent effects; Steric effects; Modified field effect; Electrical effect transmission; Solvolysis; Norbornanes; Bicyclo[2,2,2]octanes.