1. Bayliss, N. S. Quart. Rev. Chem. Soc. 6, 319 (1952).
2. Salem, L. The Molecular Orbital Theory of Conjugated Systems (Benjamin, New York, 1966).
3. Simpson, W. T. Theories of Electrons in Molecules (Prentice-Hall, Englewood Cliffs, 1962); J. Am. chem. Soc. 73, 5359 (1951); 77, 6164 (1955); 78, 3585 (1956).
4. Nature 243, 7 (1973).
5. Hausser, K. W., Kuhn, R., Smakuia, A. & Kreuchen, K. H. Z. phys. Chem. B29, 363 (1935).