摘要：

This paper has been concerned with a necessary addendum to the chemist's view of a molecule. Localized orbitals or groups of orbitals may interact with each other directly, through space, or indirectly, through other bonds in the molecule. The latter interaction may operate over surprisingly long distances. The primary effects of such interaction and their most direct measure are through ionization potentials and electronic spectra. Stability and reactivity are affected as well. The analysis of these interactions is most conveniently made through the language of perturbation theory; here, as everywhere, the role of symmetry is paramount.

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