Die Elektronenspektren des Azulenium‐ und des Heptalenium‐Kations

The electronic absorption spectra of the azulenium cation (II), the 1,2‐benzo‐azulenium cation (VII), the 5,6‐benzoazulenium cation (IX), the cations obtained from 4,5‐benzoazulene and the heptalenium cation (V) have been interpreted on the basis of a «molecules in molecules» model. The longwave bands of the spectra quoted are shown to be essentially charge‐transfer bands, the position of which is indicative of an effective electron affinity of the tropylium cation of −6,4 eV and of −6,2 eV for the benztropylium cation.