The @L03551@ \[\log _{10}k_{\text{N}} = \log _{10}k_{0}+N_{\text{+}}\] applied to the reactions between nucleophiles and certain large and relatively @S05900@ organic cations, e.g. arenediazonium, triarylmethyl and aryltropylium cations in various solvents. \(k_{\text{N}}\) is the @O04322@ for reaction of a given @C00907@ with a given nucleophilic system (i.e. given nucleophile in a given solvent). \(k_{0}\) is the @O04322@ for the same @C00907@ with water in water, and \(N_{\text{+}}\) is a parameter which is characteristic of the nucleophilic system and independent of the @C00907@. A surprising feature of the equation is the absence of a @C01124@ of \(N_{\text{+}}\), characteristic of the substrate (cf. the \(s\) in the @S06201@), even though values of \(N_{\text{+}}\) vary over 13 log units. The equation thus involves a gigantic breakdown of the @R05186@. The equation has been extended both in form and in range of application.