1. For early reviews, see: G.A. Olah, Chem. Eng. News, 45(1967)76; Science, 168(1970)1298; Angew. Chem. Int Ed. Engl., 12(1973)173; Top. Curr. Chem., 80(1979)21; Chem. Scr., 18(1981)97.
2. The search for observable long-lived cations was steered by early kinetic, stereochemical, product studies, and the development of superacid systems. Leading investigators that contributed fundamentally to these early developments include Bartlett, Hughes, Gillespie, Ingold, Meerwein, Nenitzescu, Whitmore, Winstein, and many others. Numerous compilations of these early studies have been made. For reasons of brevity we refer to the single comprehensive general review, G.A. Olah and P.v.R. Schleyer (Eds.), Carbonium Ions, Wiley, London, Vol. I, 1968; Vol. II, 1970; Vol. III, 1972; Vol. IV, 1973; and Vol. V, 1976.
3. For recent reviews, see: G.A. Olah, G.K.S. Prakash, and J. Sommer, Superacids, Wiley, New York, N.Y., 1985, Ch. 3; G.A. Olah, G.K.S. Prakash, R.E. Williams, L.D. Field, and K. Wade, Hypercarbon Chemistry, Wiley, New York, N.Y., 1987; P. Vogel, Carbocation Chemistry, Studies in Organic Chemistry 21, Elsevier, Amsterdam, The Netherlands, 1985.
4. M. Saundrs, J. Chandrasekhar, and P.v.R. Schleyer in P. de Mayo (Ed.), Rearrangements in Ground and Excited States, Vol. 1, Academic Press, New York, 1980, Ch. 1.
5. M. Schindler, J. Am. Chem. Soc., 109(1987)1020.