When a series of structurally related substrates undergo the same general reaction or when the reaction conditions for a single substrate are changed in a systematic way, the enthalpies
and entropies of activation
sometimes satisfy the relation:
where the parameter
is independent of temperature. This equation (or some equivalent form) is said to represent an 'isokinetic relationship
'. The temperature
(at which all members of a series obeying the isokinetic relationship react at the same rate) is termed the 'isokinetic temperature
'. Supposed isokinetic relationships as established by direct correlation of
are often spurious and the calculated value of
is meaningless, because errors in
lead to compensating errors in .
Satisfactory methods of establishing such relationships have been devised.
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1129
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook