Reactivity data related to processes in which molecular receptorspromote the reaction of two simultaneously complexed reactantshave been surveyed and analyzed in terms of effective molarity(EM). Methods and criteria for the calculation of reliable EM's havebeen highlighted. Extension of a previous extrathermodynamictreatment of intramolecular reactions of bifunctional chains to theintracomplex reactions of the ternary complexes involved in two-substrate catalyzed reactions has provided a sound framework fora comparative analysis of reactivity and catalytic efficiency instructurally diverse and apparently unrelated systems.