1. E. D. Hughes, Quart. Rev. 5 (1951) 245.
2. On this subject see: C. K. Ingold, Les Réactions de la Chimie Organique, Hermann et Cie, Paris, 1948, p. 27.
3. K. Fukui, H. Kato and T. Yonezawa, Bull. Chem. Soc. Japan 33 (1960) 1201.
4. C. Sandorfy and R. Daudel, Compt. Rend. Acad. Sci. 238 (1954) 93.
5. F. Fukui in Modem Quantum Chemistry, Ac. Press, New York, 1965, p. 49.