IN a recent paper1 pealing with the theoretical treatment of the chemistry of some non-benzenoid hydrocarbons, some unexpected results were obtained for the as yet unknown hydrocarbon fulvalene (I). The π-electron densities, q, of fulvalene have been computed2, and it is found that position 2 has a lower charge than position 1. In spite of this the calculated atomic polarization energies1, A′n, which may be considered to be approximations to the relative activation energies for nucleophilic substitutions, require position 1 to be the more reactive in this type of reaction. This anomaly is understandable if the self-atom polarizability3, π, of position 1 is sufficiently greater than that of position 2. The polarizabilities have now been calculated and are compared with the π-electron densities and atomic polarization energies in Table 1. It must be concluded that the difference in polarizabilities is sufficient to cause the apparent discordance between A′n and q, and so it is likely that fulvalene will prove to be the first example of a molecule in which the static charge distribution does not provide an adequate picture of the chemical reactivity.

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  1. 1

    Brown, Trans. Farad. Soc. (in the press).

  2. 2

    Brown, Trans. Farad. Soc., 45, 296 (1949).

  3. 3

    Coulson and Longuet-Higgins, Proc. Roy. Soc., A, 191, 39 (1947).

  4. 4

    Coulson, Proc Roy. Soc., A, 169, 413 (1939).

  5. 5

    Brown, Aust. J. Sci. Res., A (in the press).

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BROWN, R. Fulvalene. Nature 165, 566–567 (1950) doi:10.1038/165566b0

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