The term applies to either of the equations:
(or their logarithmic forms) where
,
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
protondron ). 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.
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
