Correlation between alkyl cation affinities and proton affinities - a means to rationalise alkyl group substituent effects

Using literature thermochemical data it is demonstrated that the known linear relationship between proton affinities and methyl cation affinities can be extended to other alkyl groups (ethyl, i-propyl, t-butyl), It is suggested that the slopes of the straight lines can be used to define a new set of alkyl substituent constants.