Electrical Effects of Substituent Groups in Saturated Systems. Reactivities of 4-Substituted Bicyclo [2.2.2]octane-1-carboxylic Acids

Abstract

The reactivities of a series of 4-substituted bicyclo[2.2.2]octane-1-carboxylic acids and esters with X = -H, -OH, -CO_2 C_2H_5, -Br and -C≡N have been determined. The apparent ionization constants of the acids in 50% aqueous ethanol at 25º, the reactivities of the acids toward diphenyldiazomethane in ethanol at 30°, and the saponification rates of the ethyl esters were measured and found to parallel one another throughout the series. The order of reactivities with the various substituents at the 4-position was -C≡N > -Br > -CO_2C_2H_5> -OH > -H. Although transmission of electrical effects of substituent groups through the bicyclo[2.2.2]octane ring system is not possible by resonance interaction involving conjugated unsaturation, the magnitudes of the substituent influences were found to be comparable to those observed in m- and p-substituted benzene derivatives. The Kirkwood-Westheimer ellipsoidal cavity model for calculation of electrostatic effects of polar substituent groups on reactivity gives qualitative agreement with the experimental results.

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