Wiberg, Kenneth B. Substituent Effects on the Acidity of Weak Acids. 1. Bicyclo[2.2.2]octane-1-carboxylic Acids and Bicyclo[1.1.1]pentane-1-carboxylic Acids The acidities of 3- and 4-substituted bicyclooctane-1-carboxylic acids and 3-substituted bicyclo[1.1.1]pentane-1-carboxylic acids have been calculated at the MP2/6-311++G** theoretical level. There is good agreement between the calculated and observed gas-phase acidities. The acidities of the 4-substituted bicyclooctane acids were found to be linearly dependent on the C−X bond dipoles, as expected from a field effect. The substituents had a negligible effect on the electron density at C1. The difference in acidity between 4-chlorobicyclo[2.2.2]octane-1-carboxylic acid and the parent acid (6.2 kcal/mol) is reproduced by the Kirkwood−Westheimer treatment of substituent effects on acidity, but only if the bicyclooctane ring is given an effective dielectric constant of unity. The acidities of the 3-substituted bicyclooctane acids are linearly related to the corresponding 4-substituted acids with a slope of 0.9. The acidities of the 3-substituted bicyclo[1.1.1]pentane-1-carboxylic acids are linearly related to the C−X bond dipoles for this ring system (which are different than those for the bicyclooctanes), and they are also linearly related to the acidity of the 4-substituted bicyclo[2.2.2]octanecarboxylic acids with a slope of 1.34. The larger slope is due to the smaller bridgehead−bridgehead distance in the bicyclopentane ring than in bicyclo[2.2.2]octane. bicyclooctane acids;aciditie;MP 2002-02-05
    https://acs.figshare.com/articles/journal_contribution/Substituent_Effects_on_the_Acidity_of_Weak_Acids_1_Bicyclo_2_2_2_octane-1-carboxylic_Acids_and_Bicyclo_1_1_1_pentane-1-carboxylic_Acids/3690846
10.1021/jo011051x.s001