The @[email protected] of the form: \[\log _{10}(\frac{k}{k_{0}})=s\ n\] applied to the variation of @[email protected] of a given @[email protected] @[email protected] towards a series of nucleophilic reagents. \(n\) is characteristic of the @[email protected] (i.e. a measure of its @[email protected]) and \(s\) is characteristic of the substrate (i.e. a measure of its sensitivity to the @[email protected] of the @[email protected]). A scale of \(n\) values is based on the rate coefficients \(k\) for the reaction of methyl bromide with nucleophiles in water at \(25\ ^{\,\unicode{x26ac}}\text{C}\), \(s\) being defined as 1.00 for these reactions and \(n\) being defined as 0.00 for the @[email protected] of methyl bromide. (Other scales have been devised.)
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1169 [Terms] [Paper]