The formulation of the second-order perturbation approach to the stabilization energy of the A-B interacting species due to charge transfer is revisited. Intrinsic (i.e., electronic) theoretical indices for both relative electrophilicity and nucleophilicity are proposed for any electrophile (A)-nucleophile (B) pairs of combining species. By using the new descriptors, an electronic analogue to the Mayr-Patz linear free relationship has been successfully tested in the context of available experimental evidence reported for reactions of primary and secondary amines with benzhydrylium ions.