1. Olah G A and Schleyer P v R 1969Carbonium ions (New York, London, Sydney, Toronto: Wiley-Interscience) vol. 2; Olah G A and Schleyer P v R 1971Carbonium ions (New York, London, Sydney, Toronto: Wiley-Interscience) vol. 3; Creary X 1991Chem. Rev. 91 1625
2. Vogel P 1985Organic chemistry: Studies in organic chemistry 21 (New York: Elsevier Science) ch. 10; Saunders M and Jiminez-Vazquez H A 1991Chem. Rev. 91 375
3. Pine S H 1987Organic chemistry 5th edn (Singapore: McGraw-Hill) p. 973
4. Sykes P 1986A guide book to mechanism in organic chemistry 6th edn (New Delhi: Orient Longman) p. 1ll
5. Fittig W 1859Annalen 110 23; Fittig W 1860Annalen 114 54