From idea to long-lived carbocations

At the beginning of the 20th century it was not known that reaction mechanisms make use of short-lived reactive intermediates, but the idea was born at about that time. In 1922 the German chemist H. Meerwein explained his results from studies of the kinetics of a rearrangement reaction by suggesting that carbocations were formed as intermediates.
    During the 1930s C.-K. Ingold and E.D. Hughes in England and later S. Winstein in the USA performed detailed kinetic investigations of substitution and elimination reactions. They found that in many of these reactions carbocations were intermediates. But they were so short-lived and appeared in such low concentrations that they could not be directly observed with physical methods.
    The reason the carbocations are short-lived is their extreme reactivity towards surrounding molecules e.g. solvent molecules or negative ions (nucleophiles).
    During the 1950s Olah and his co-workers, building on results obtained by Meerwein in the 1940s, studied complexes which acylfluorides and alkylfluorides form with borontrifluoride, BF₃, and other Lewis acids.
    At the beginning of the1960s Olah made the pioneering discovery that he could prepare long-lived stable alkyl cations if he used even stronger acids than BF₃. He chose the superacid antimon-pentafluoride SbF₅.