1. Z. V. Todres, F. M Stoyanovich, Ya. L. Gol'dfarb, and D. N. Kursanov, Khim. Geterotsikl. Soedin., 632 (1973).
2. J. Pople, Trans. Faraday Soc., 49, 1375 (1953).
3. E. Strom and G. Russell, J. Am. Chem. Soc., 87, 3326 (1965).
4. V. V. Plemenkov and E. G. Kataev, in: The Structure of Molecules and Quantum Chemistry [in Russian], Izd-vo Naukova Dumka, Kiev (1970), p. 142.
5. M. Kamiya, Bull. Chem. Soc. Japan, 43, 3344 (1970).