Hammett acidity function

The Hammett acidity function, denoted as \( H \), is a quantitative measure of acidity in solutions, especially in non-aqueous solvents. It was introduced by the chemist Louis Hammett in the context of studying the acidity of different substances and their effects on chemical reactions. The function is particularly useful because it allows for a comparison of the acidity of various proton donors (acids) under varying conditions and in different solvents.