1. See e.g.: Allinger, N. L., Cava, M. P., De Jongh, D. C., Johnson, C. R., Lebel, N. A., Stevens, C. L.: Organic chemistry. New York, N.Y.: Worth Publishers 1971
2. Snyder, L. C., Basch, H.: J. Am. Chem. Soc. 91, 2189 (1969)
3. Hart, B. T.: Aust. J. Chem. 26, 461, 477 (1973)
4. Leroy, G., Sana, M.: Theoret. Chim. Acta (Berl.) 33, 329 (1974)
5. Lievin, J., Verhaegen, G.: to be published