Correlating Acidities, Electron Affinities, and Bond Dissociation Energies. Measure One, Get All Three!

Abstract

Bond energies, acidities, and electron affinities are related in a thermodynamic cycle, and by measuring two of these quantities one can derive the third. This procedure is most often used to determine bond dissociation energies. In this work, we show that Delta H(o)(acid)(HX), EA(X(*)), and BDE(HX) are all linearly related for specific classes of compounds (e.g., alcohols and carboxylic acids), and therefore, only one of these quantities is needed to determine the others. This should simplify thermodynamic determinations and enable hundreds of new values to be obtained from already existing data in the literature. The intercepts obtained from plots of Delta H(o)(acid)(HX) vs EA(X(*)) provide bond energies which correspond to BDE(HX) when EA(X(*)) = 0. The results for eight different types of compounds are provided and some of these values are discussed. Sensitivity factors are obtained from the slopes of these plots, and their sign (+ vs -) can be predicted by considering physical effects such as hybridization and resonance.