A reaction (actual or hypothetical) in which the types of bonds that are made in forming the products are the same as those which are broken in the reactants, e.g.
Such processes have advantages for theoretical treatment. The Hammett equation as applied to equilibria [cf. (a)] essentially deals with isodesmic processes.
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1128 (https://doi.org/10.1351/pac199466051077)