The equation in the form
lg(k/ko) =
or
lg(K/Ko) =
applied to the influence of meta- or para-substituents X on the reactivity of the functional group Y in the benzene derivative m- or p-XC6H4Y. k or K is the rate or equilibrium constant, respectively, for the given reaction of m- or p-XC6H4Y; ko or Ko refers to the reaction of C6H5Y, i.e. X = H; is the substituent constant characteristic of m- or p-X; is the reaction constant characteristic of the given reaction of Y. The equation is often encountered in a form with lg ko or lg Ko written as a separate term on the right hand side, e.g.
lg k = + lg koor
lg K = + lg KoIt then signifies the intercept corresponding to X = H in a regression of lg k or lg K on . HAMMETT (1940, 1970). See also -value, -constant, Taft equation, Yukawa-Tsuno equation.
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