An attempt at interpretation of the goulden plot in terms of an isokinetic relationship

Abstract

On the basis of precise ν_OH measurements and carefully checked pK_a values the Goulden plot for substituted benzoic acids, acetylenic acids, and phenols has been reinvestigated: even for families of acids of similar structure the fit is not good. The same is found for the gas-phase pK_a data. It is shown that the isokinetic temperature for the above acids is in the range 0 < β < T; the dominant contribution to δΔG comes from the δΔS term. Moreover β values for these reaction series are not constant which means there is a varying blend of δΔH and δΔS in δΔG. This in turn leads to deviations from the δΔG–ν_OH plot, since ν_OH is mostly related to internal changes in enthalpy.