ABSTRACT
Although organic ion-radicals differ from their corresponding parent (uncharged) molecules only by one electron, this difference can lead to large modi cations not only in terms of their chemical reactivity but also to fundamental stereochemical changes. Several reviews have focused on this feature of ion-radical organic chemistry (Todres 1974, Pedulli 1993). The electron transfer obeys the Franck-Condon principle and takes place within such a short time that there is no nuclear motion. However, many organic compounds can oscillate between diverse conformational isomers, and one-electron transfer can trigger one of them. Only those isomers that are the most favorable for the existence of an unpaired electron on the corresponding somomer can be triggered. Somomers are electromers differing in their SOMO. Thus, the tube conformation is the most stable for cyclooctatetraene. The tube conformer can exist as a bath standing normally or as a bath turned over. The at cyclooctatetraene de nitely exists between the normal and turned conformers. The cyclooctatetraene anion-radical is a planar or an almost planar species. The planar, 9-π electron anion-radical structure of cyclooctatetraene is closer to the aromatic (planar and stabilized) structure of the dianion with 4n + 2 = 10-π electrons than that of the parent neutral molecule. This is the reason why one-electron transfer is able to trigger the intermediary at conformation of cyclooctatetraene (Scheme 6.1). Naor and Luz (1982) made a stand for this point of view. This feature agrees with the Franck-Condon principle and with the thermodynamic demand of similarity between structures of the transition state and the product.
