Hammett equation

The Hammett equation is a linear free-energy relationship in physical organic chemistry, connecting the rates and equilibrium constants of many reactions of benzoic acid derivatives. It was developed by Louis Plack Hammett, who published it in 1937 as an extension of his 1935 work on chemical reactivity. In its basic form the equation states log(K/K0) = sigma*rho, linking a substituent constant sigma, which reflects how a given substituent affects a reaction, with a reaction constant rho that characterizes the sensitivity of a particular reaction to substituent effects. Hammett introduced the relationship empirically, from observed data rather than from a prior theoretical derivation, and it remains a standard tool for predicting and rationalizing how structural changes to a molecule affect its reaction behavior. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/