Photoelectron Spectra of Azabenzenes and Azanaphthalenes: III. The orbital sequence in methyl‐ and trimethylsilyl‐substituted pyridines

The ionization potentials of methyl‐, t‐butyl‐ and trimethylsilyl‐substituted pyridines have been determined by high‐resolution photoelectron spectroscopy. The results are discussed in terms of destabilizing inductive and stabilizing conjugative effects of the substituents, and have been parametrized on the basis of a HMO‐type perturbation treatment. Our data are in accord with the idea that the topmost occupied orbital in pyridine is a ‘lone pair’ orbital.