Related Experiment Video
Updated: Aug 1, 2026

Determination of the Gas-phase Acidities of Oligopeptides
Published on: June 24, 2013
Correlating acidities, electron affinities, and bond dissociation energies. Measure one, get all three!
Alireza Fattahi1, Steven R Kass
1Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA.
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.
Related Concept Videos
Bond Energies and Bond Lengths
Acid/Base Strengths and Dissociation Constants
Acid Strength and Molecular Structure
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
Molecular Geometry and Dipole Moments
Bond Dissociation Energy and Activation Energy
Molecular Structure and Acidity
The size effect explains the change in atomic size on acidity. When comparing the acids formed from elements that belong to the same column in the periodic table, their atomic sizes...

