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  • 1
    Electronic Resource
    Electronic Resource
    Electron-Transfer Chemistry and Redox-Switching of Stilbene-Like Heteroaromatic Compounds  -  Syntheses, Optoelectrochemical and ESR/ENDOR StudiesDedicated to Prof. M. Hanack on the occasion of his 65th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 2069-2077 
    Details
    ISSN: 0947-3440
    Keywords: Stilbenes ; Push-pull substitution ; Electron transfer ; (Z)/(E) Isomerisation ; Radical ions ; Cyclic voltammetry ; Spectroelectrochemistry ; ESR / ENDOR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Redox-active compounds, in which the electron donor and the acceptor subunits are covalently linked by a vinylene spacer group were synthesised and their properties were investigated by cyclovoltammetry, spectroelectrochemistry, and ESR/ENDOR spectroscopy.  -  10-Methylphenothiazinyl, 10-methylphenoxazinyl, and phenoxathiinyl were used as electron-donating groups whereas 9,10-anthraquinon-2-yl and phenyl groups were employed as acceptors. The synthesis of the push-pull-substituted stilbenes 1a, 1b, 1c, 2a, 2b and 2c was achieved by Wittig coupling of the heterocyclic aldehydes with the anthraquinoyl or phenyl phosphonium salts. The diastereoisomers were separated either by chromatography or by crystallization.  -  The redox potentials of the (Z) and (E) isomers differ only slightly. Spectroelectrochemical measurements indicate that the radical cations of the phenothiazine and phenoxazine derivatives undergo rearrangement from the (Z) to the (E) isomers. On the other hand, electron attachment leads to configurationally stable radical anions. This behaviour is rationalised in terms of the electron distribution reflected by the hyperfine data established by ESR/ENDOR spectroscopy.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961218
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  • 2
    Electronic Resource
    Electronic Resource
    Elektronentransferchemie chinoider Verbindungen: Chemische, elektrochemische und UV/VIS-spektroelektrochemische Untersuchungen von Acenazulendionen (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 727-735 
    Details
    ISSN: 0009-2940
    Keywords: Quinones ; Electron exchange ; Radical ions ; Cyclic voltammetry ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Electron-Transfer Behaviour of Quinoid Compounds: Acenazulenediones - A Study by Chemical and Electrochemical Methods and by UV/VIS SpectroelectrochemistryIn contrast to arene-condensed benzoquinones, polycyclic 1,4-quinones (Q) containing azulenoid partial structurs dimerize on reduction to their radical anions. These investigations were undertaken with naphth[2,3-a]azulene-5,12-dione (1), azuleno[1,2-b]anthracene-6,13-dione (8), benzazulenediones 10, and with benz[a]anthracene-7,12-dione (9). Evidence which originally came from cyclovoltammetry is now confirmed by spectroscopic data (UV/VIS spectroelectrochemistry) and by chemical reduction with sodium metal. The equilibrium 2 Q·- ⇌ (Q-Q)2- depends strongly on structural details. In case of extended arene condensation it is shifted to the dimeric. The structure and the electron transfer behaviour of the dimeric dianions (Q-Q)2- are determined. The radical anions (Q)·- are characterized by their UV/VIS spectra obtained from UV/VIS spectroelectrochemistry. A qualitative evaluation of the strength of the central bond in the radical anions (Q-Q)·- as well as in the dianions (Q-Q)2- and the radical trianions (Q-Q)3·- is given. Some chemical and physical properties of the radical cation 1·+ are reported.
    Notes: Polycyclische Chinone (Q) mit azulenoiden Teilstrukturen dimerisieren bei der Reduktion zu den Radikalanionen. Die konstitutionsisomeren arenkondensierten Verbindungen zeigen dieses Verhalten nicht. Dies wird am Beispiel von Naphth[2,3-a]azulen-5,12-dion (1), Azuleno[1,2-b]anthracen-6,13-dion (8), Benzazulendionen 10 und Benz[a]anthracen-7,12-dion (9) gezeigt. Erste Hinweise für die Ursache dieses Verhaltens stammen aus Untersuchungen mit der Cyclovoltammetrie. Eine Bestätigung dieser Ergebnisse erfolgt jetzt durch spektroskopische Daten (UV/VIS-Spektroelektrochemie) und durch die chemische Reduktion mit Natrium. Die Lage des Gleichgewichts 2 Q·- ⇌ (Q-Q)2- ist strukturabhängig. Die Strukturen der dimeren Dianionen (Q-Q)2- und der Radikalanionen (Q)-) werden durch Elektronenspektroskopie und teilweise durch 1H-NMR charakterisiert und zugeordnet. Die Stärke der zentralen Bindung der Radikalanionen (Q-Q)·-, Dianionen (Q-Q)2- und Radikaltrianionen (Q-Q)3·- wird qualitativ abgeschätzt. Über einige chemische und physikalische Eigenschaften des Radikalkations 1·+ wird außerdem berichtet.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891220421
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