, 
and 
are constants for a given reaction series (
and 
are called 'Brønsted exponents'), 
and 
are catalytic coefficients (or rate coefficients) of reactions whose rates depend on the concentrations of
HA
and/or of
A−
. 
is the acid dissociation constant of the acid HA, 
is the number of equivalent acidic protons in the acid HA, and 
is the number of equivalent basic sites in its conjugate base A−. The chosen values of 
and 
should always be specified. (The charge designations of
H
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 
, 
, 
for leaving group, nucleophile and equilibrium constants, respectively.
See also: linear free–energy relation
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1091
PAC, 1996, 68, 149
(A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC
Recommendations 1996))
on page 154