1. R. W. Taft, chapter 2.
2. E. M. Arnett, Accounts Chem. Research, 6, 404 (1973).
3. F. M. Jones, III and E. M. Arnett, Progr. Phys. Org. Chem., 11, 263 (1974).
4. E. M. Arnett and G. Scorrano, Adv. Phys. Org. Chem., in press.
5. R. P. Bell, The Proton in Chemistry, second edition, Chapman and Hall, London (1973).