This term applies in a general way to any multiparametric extension of the Hammett equation
. It is sometimes used specifically for a form of dual substituent-parameter equation
in which the actual value of the correlated property
under the influence of the substituent X is used, rather than the value relative to that for
An intercept term
corresponding to the value of
is introduced, e.g.
The equation may be applied to systems for which the inclusion of further terms to represent other effects, e.g. steric, is appropriate.
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1114
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