"Ingold, Hughes, and their collaborators in England, starting in the late 1920s, carried out detailed kinetic and stereochemical investiga tions on what became known as nucleophilic substitution at saturated carbon and polar elimination reactions. Their work relating to uni molecular nucleophilic substitution and elimination, called SN1 and E1 reactions, in which formation of carbocations is the slow rate determining step, laid the foundation for the role of electron-deficient carbocationic intermediates in organic reactions."