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The term applies to either of the equations
kHA/p = G(KHAq/p)kA/q = G(KHAq/p)-(or their logarithmic forms) where , and G are constants for a given reaction series ( and are called "Brønsted exponents"), kHA and kA are catalytic coefficients (or rate coefficients) of reactions whose rates depend on the concentrations of HA and/or of A-. KHA is the acid dissociation constant of the acid HA, p is the number of equivalent acidic protons in the acid HA, and q is the number of equivalent basic sites in its conjugate base A-. The chosen values of p and q should always be specified. (The charge designations of HA and A- are only illustrative.)
The Brønsted relation is often termed the "Brønsted catalysis law" (or the "Catalysis Law"). Although justifiable on historical grounds, this name is not recommended, since Brønsted relations are known to apply to many uncatalysed and pseudo-catalysed reactions (such as simple proton (hydron) transfer reactions). The term "pseudo-Brønsted relation" is sometimes used for reactions which involve nucleophilic catalysis instead of acid-base catalysis. Various types of Brønsted parameters have been proposed such as lg, nuc, eq for leaving group, nucleophile and equilibrium constants, respectively. See also linear free-energy relation.
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