1. Labhart, H., Wagnière, G.: Helv. Chim. Acta 42, 2219 (1959).-Cookson, R. C., Wariyar, N. S.: J. Chem. Soc. 1956, 2302.
2. Moscowitz, A.: Proc. Roy. Soc. (London), Ser. A 297, 40 (1967).-Cookson, R. C.: Proc. Roy. Soc. (London), Ser. A 297, 27 (1967).-Murrell, J. N. in: The theory of the electronic spectra of organic molecules, p. 167, New York, J. Wiley & Sons 1963.-Winstein, S., de Vries, L., Orloski, R.: J. Am. Chem. Soc. 83, 2020 (1961).-Kosower, E. M., Closson, W. D., Goering, H. L., Gross, J. C.: J. Am. Chem. Soc. 83, 2013 (1961).-Cookson, R. C., Hill, R. R., Hudec, J.: Chem. Ind. 1961, 589.
3. Höhn, E. G., Weigang, Jr., O. E.: J. Chem. Phys. 48, 1127 (1968).-Bays, D. E., Cookson, R. C., MacKenzie, S.: J. Chem. Soc. B 1967, 215.-Mason, S. F.: Quart. Rev. 17, 20 (1963).-Moskovitz, A., Mislow, K., Glass, M. A. W., Djerassi, C.: J. Am. Chem. Soc. 84, 1945 (1962).
4. Chadwick, D., Frost, D. C., Weiler, L.: J. Am. Chem. Soc. 93, 4320, 4962 (1971).
5. Marsh, G., Kearns, D. R., Schaffner, K.: J. Am. Chem. Soc. 93, 3129 (1971).