the Hammett equation

The Hammett equation describes how different chemical groups attached to a molecule influence the molecule's reactivity, especially in reactions involving acids and bases. It uses a numerical value called a "sigma constant" to represent the effect of a substituent on reaction rates or equilibrium. When combined with a reaction-specific factor called the "reaction constant," the equation helps predict how changing parts of a molecule will alter its behavior. Essentially, it provides a way to quantify and understand the impact of different chemical groups on reaction outcomes, aiding chemists in designing and analyzing reactions more effectively.