THE linear relation (1) between the activation enthalpies ΔH‡ and activation entropies ΔS‡ in a series of related reactions is called the isokinetic relationship and is—if valid for a certain series—of fundamental importance in reaction kinetics and in reactivity studies1–4. The slope β, called the isokinetic temperature, has an important physical meaning; it represents a temperature at which all reactions of the series should proceed at the same rate.