The @[email protected] \[\log _{10}k_{\text{N}} = \log _{10}k_{0}+N_{\text{+}}\] applied to the reactions between nucleophiles and certain large and relatively @[email protected] organic cations, e.g. arenediazonium, triarylmethyl and aryltropylium cations in various solvents. \(k_{\text{N}}\) is the @[email protected] for reaction of a given @[email protected] with a given nucleophilic system (i.e. given nucleophile in a given solvent). \(k_{0}\) is the @[email protected] for the same @[email protected] with water in water, and \(N_{\text{+}}\) is a parameter which is characteristic of the nucleophilic system and independent of the @[email protected] A surprising feature of the equation is the absence of a @[email protected] of \(N_{\text{+}}\), characteristic of the substrate (cf. the \(s\) in the @[email protected]), even though values of \(N_{\text{+}}\) vary over 13 log units. The equation thus involves a gigantic breakdown of the @[email protected] The equation has been extended both in form and in range of application.