Grunwald–Winstein equation

Hammett used the ionization of benzoic acid as the standard reaction to define a set of substituent parameters σX, and then to generate the ρ values, which represent ionizing abilities of different substrates.

Following this idea, Grunwald and Winstein plotted the relative rate constant vs. the change of solvent system, and formulated this behavior in the Grunwald–Winstein equation.

In equation 2, kt-BuCl, 80% EtOH stands for the rate constant of t-BuCl reaction in 80% aqueous Ethanol, which is chosen as the reference.

The variable kt-BuCl, sol stands for the rate constant of the same reaction in a different solvent system, such as ethanol-water, methanol-water, and acetic acid-formic acid.

The equation parameter m, called the sensitivity factor of solvolysis, describes the compound’s ability to form the carbocation intermediate in given solvent system.