The Brønsted catalysis equation or law of correlation, after Johannes Nicolaus Brønsted, gives the relationship between acid strength and catalytic activity in general acid catalysis.
[1] A plot of the common logarithm of the reaction rate constant k versus the logarithm of the ionization constant Ka for a series of acids (for example a group of substituted phenols or carboxylic acids) gives a straight line with slope α and intercept C. The Brønsted equation is a free-energy relationship.
When the relationship is not linear, the chosen group of catalysts do not operate through the same reaction mechanism.
Reactions that have low values for proportionality constants α or β are considered to have a transition state closely resembling the reactant with little proton transfer.
With a high value, proton transfer in the transition state is almost complete.