1. L. P. Hammett, Physical Organic Chemistry, 2nd edition, p. 347 (McGraw-Hill, New York, 1970).
2. J. E. Leffler and E. Grunwald, Rates and Equilibria of Organic Reactions, p. 128 (Wiley, New York, 1963).
3. N. B. Chapman and J. Shorter, eds., Advances in Linear Free Energy Relationships (Plenum, London, 1972).
4. L. P. Hammett, Physical Organic Chemistry, Chap. 7 (McGraw-Hill, New York, 1940).
5. Reference 1, p. 355.