That the decrease in R, on monosubstitution in the 3position, is not reflected in a change of may be attributed to the only other variable in eq. 5, i.e., DE. The term DE is a dielectric constant in name only, being a function of the shape of the molecule (for a spherical model the square of the ratio of the distance of the protons from the center of the sphere and the radius of the sphere), the dielectric constant of the molecule, and the dielectric constant of the solvent.The lack of sensitivity of ^ to changes in R on monosubstitution may be ascribed to an opposite and almost equal change in DE. In unsubstituted glutaric acid the electrostatic influence of carboxyl groups occur primarily through the low dielectric of the molecular backbone since, due to solvation of the polar carboxyl groups, the molecule exists in an extended conformation. Monosubstitution in the 3-position brings about a decrease in R accompanied by a greater fraction of the electrostatic effect occurring through the high dielectric of the solvent, and the decrease in R is matched by an increase in DE so that the product of DeR in eq. 5 is not significantly altered. The conformational changes brought about by 3-gem substitution are greater than those brought about by the monosubstituents examined, and most of the electrostatic interaction occurs through the solvent so that DE is essentially constant and the product of RDE becomes smaller with increasing steric requirements of the gem substituents.By the reasoning presented above the similar influence of 3-gem substitution on log Ki/Ko and log kT[k0 and the grossly greater sensitivity of log kT/k0 to 3-monosubstitution is explained.

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