Abstract
Electron-transmission spectroscopy has been employed in a study of the temporary negative-ion states of 2-, 3- and 4-methylpyridine, 2-, 3- and 4-chloropyridine, 2-, 3- and 4-aminopyridine, 2-, 3- and 4-acetylpyridine and 2- and 4-vinylpyridine. The effect of substitution on the normally unoccupied orbitals, as well as that of replacement of a CH group by a nitrogen atom, is found to be related to the coefficient of the molecular orbital at the site of substitution. The latter effect, however, is much less pronounced for the unfilled than for the filled orbitals. We attribute this to changes in geometry of the aza derivatives and to the greater diffuseness of the anion wavefunction compared with that of the cation. A simple Hückel MO treatment, the equivalent of the LCBO method for filled orbitals, is applied to the unfilled orbitals of the vinylpyridines and acetylpyridines, and yields the energies of these short-lived anion states quite satisfactorily.
Published Version
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