Hammett equationIUPAC Term

The equation in the form: \[\log _{10}(\frac{k}{k_{0}}) \rho \ σ \] or \[\log _{10}(\frac{K}{K_{0}}) \rho \ σ \] applied to the influence of i meta /i - or i para /i -substituents X on the reactivity of the functional group Y in the benzene derivative i m /i - or i p /i -XC sub 6 /sub H sub 4 /sub Y. k or K is the rate or equilibrium constant, respectively, for the given reaction of i m /i - or i p /i -XC sub 6 /sub H sub 4 /sub Y; k0 or K0 refers to the reaction of C sub 6 /sub H sub 5 /sub Y, i.e. X H; is the substituent constant characteristic of i m /i - or i p /i -X: is the reaction constant characteristic of the given reaction of Y. The equation is often encountered in a form with log 10 k 0 or log 10 K 0 written as a separate term on the right hand side, e.g. \[\log _{10}k \rho \ σ \log _{10}k_{0}\] or \[\log _{10}K \rho \ σ \log _{10}K_{0}\] It then signifies the intercept corresponding to X H in a regression of log 10 k or log 10 K on σ.