1. For a comprehensive review up to ‘70’s see: Swarc M. Ion and Ion Pairs in Organic Reactions. New York: Wiley Int., vol. 1, 1972, vol. 2, 1974.
2. Freed J.N. J. Phys. Chem. 71, 38 (1967)
3. Hudson A., Luckhurst G.R. Chem. Rev. 69, 191 (1967)
4. Atherton N.M. Electron Spin Resonance, chap. 8 and 9. Chichester: Hellis Horwood Ltd. 1972.
5. Atherton N.M., Weissman S.J. J. Am. Chem. Soc. 83, 1330 (1961)