1. Williams, G. H.: Homolytic Aromatic Substitution. London.: Pergamon Press 1960.
2. Hey, D. H.: Advances in free radical chemistry (ed. G. H. Williams), Vol. II, p. 47. London: Logos-Academic 1967.
3. Williams, G. H.: Special publication N. 24, p. 25. London: The Chemical Society 1970.
4. Perkins, M. J.: Free radicals (ed. J. K. Kochi), Vol. II, p. 231. New York: Wiley and Sons 1973.
5. Hey, D. H., Orman, S., Williams, G. H.: J. Chem. Soc. 1961, 565.