A discussion of the Hammett acidity function. Study of some weak bases
Abstract
Important variations in the pKa values of several weak bases have been obtained by using different acidity functions Ho valid for HCIO4 and with the application of the Hammett equation; these discrepancies may be reduced by using a corrected form of the Hammett equation in which the ratio intercept slope is constant and coincides with the pKa irrespective of the H0 function utilized; the smallest standard deviations are observed within the range log I 1 to –1. The H+ and HR functions are not well behaved, even for cationic bases such as o-phenylenediamine, adenine, and guanine. All these results may be interpreted by a linear relationship among the activity coefficients.