1. Gaspar,P.P., Hammond,G.S.: In: Kirmse,W. (Ed.): Carbene chemistry. New York: Academic Press 1964
2. Closs,G.: Topics Stereochem. 3, 198 (1968)
3. Bethell,D.: Advan. Phys. Org. Chem. 7, 153 (1969)
4. Braun,W., Bass,A.M., Pilling,M.: J. Chem. Phys. 52, 5131 (1970)
5. Herzberg,G.: Proc. Roy. Soc. (London) A 262, 291 (1961)