1. D. Lloyd, D. R. Marshall, Angew. Chem. 184, 447 (1972);
2. D. Lloyd, D. R. Marshall, Angew. Chem., Int. Ed. Engl. 11, 404 (1972)
3. D. Bryce-Smith, H. C. Longuet-Higgins, Chem. Comm. 1966, 593
4. M. J. S. Dewar, The Molecular Orbital Theory of Organic Compounds, McGraw-Hill, New York, N. Y. 1969
5. B. A. Hess, jr., L. J. Schaad, J. Am. Chem. Soc. 93, 305 (1971)