1971 Volume 44 Issue 3 Pages 682-686
The ground-state electronic properties and electronic spectra of pyracylene (I), acepleiadylene (II), and dipleiadiene (III) have been studied by using the semi-empirical SCF LCAO-π-MO method, which allows for bond order-bond length correlation at each iteration. It is shown that the I and III molecules do not belong to, respectively, the pentalenoid and heptalenoid systems, as was expected from the HMO energy diagram. The predicted chemical reactivities, diamagnetic anisotropics, and electronic spectra for I and II are in good agreement with the available experimental data. The calculated C–C bond lengths indicate that the I, II, and III molecules are all both aromatic and polyolefinic. The upfield shift of the NMR spectrum and the unusually low value of the first half-wave potential for I can be well explained in terms of, respectively, the diamagnetic anisotropy and the energy of the lowest vacant SCF MO, calculated by using the predicted equilibrium configuration that corresponds to the aromatic model (Ia).
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