title: Delocalized carotenoid cations in relation to the soliton model.
abstract: A series of charge-delocalized carotenoid mono- and dications have been prepared by treatment of selected carotenoids with Brønsted and Lewis acids. The detailed structures of the carbocations were established by NMR studies in the temperature range from -10 to -20 degrees C. The general strategy for structure elucidation by NMR of several cationic components in a mixture is outlined. Bond type and regions of bond inversion were established, as well as the charge distribution, which was determined from the difference in (13)C chemical shift at each carbon. This method gave a more accurate estimate for the partial charges than by using the Spiesecke-Schneider relationship. The resulting charge distribution was used as models for the structure of charged solitons. These carotenoid cations have the most delocalized charge so far determined, and the monocations represent the first experimental structure determination of positively charged solitons. The soliton width determined here is in good agreement with the results of previous AM1 calculations.
authors.affiliation: Department of Chemistry, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors.forename: Bjart Frode
authors.initials: BF
authors.lastname: Lutnaes
authors.forename: Geir
authors.initials: G
authors.lastname: Kildahl-Andersen
authors.forename: Jostein
authors.initials: J
authors.lastname: Krane
authors.forename: Synnøve
authors.initials: S
authors.lastname: Liaaen-Jensen
mesh_terms: D001880:Boranes / Q000737:chemistry; D002338:Carotenoids / Q000138:chemical synthesis / Q000737:chemistry*; D002412:Cations; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008968:Molecular Conformation
chemical_list: D001880:Boranes; D002412:Cations; D002338:Carotenoids; C101707:boron trifluoride etherate; C105515:echinenone