Term: proton affinity
https://doi.org/10.1351/goldbook.P04907

Definition:
The negative of the enthalpy change in the gas phase reaction (real or hypothetical) between a proton (more appropriately hydron) and the chemical species concerned, usually an electrically neutral species to give the conjugate acid of that species. Proton affinity is often, but unofficially, abbreviated as PA.

Related Terms:
1) gas-phase basicity (http://doi.org/10.1351/goldbook.G02588).
2) enthalpy (http://doi.org/10.1351/goldbook.E02141).
3) proton (http://doi.org/10.1351/goldbook.P04906-1).
4) proton (http://doi.org/10.1351/goldbook.P04906-2).
5) hydron (http://doi.org/10.1351/goldbook.H02904).
6) chemical species (http://doi.org/10.1351/goldbook.CT01038).
7) conjugate acid (http://doi.org/10.1351/goldbook.C01266).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1153 (https://doi.org/10.1351/pac199466051077)

Citation: 'proton affinity' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.P04907

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