Electrophilicity Scales for Carbocations

The systematic development of electrophilicity scales started in the early 1970s, when Ritchie reported about the kinetics of the reactions of highly stabilized carbocations, such as tritylium and tropylium ions, with anions and amines. The electrophilicity is a useful parameter for ordering carbocations according to their reactivities toward nucleophiles. Since it is possible to study the reactivities of carbocations and noncharged electrophiles toward the same nucleophiles, it becomes possible to directly link the chemistry of carbocations to that of electron-deficient noncharged aromatic and nonaromatic ? systems. The main advantage of the E scale is the possibility to combine it with the nucleophilicity scale N for predicting reactivities and selectivities of a large variety of polar organic reactions. This chapter shows applications of the E scale.