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1996 (1)
1995 (1)
1Author    Andreas John, Hans BockRequires cookie*
 Title    Elektronentransfer und Kontaktionen-Bildung, 42 [1,2] Cyclovoltammetrische und ESR/ENDOR-Untersuchungen der Einelektronen-Reduktion von Diphenochinonen Electron Transfer and Contact Ion Pair Formation, 42 [1,2] Cyclovoltammetric and ESR/ENDOR Investigations of the One-Electron Reduction of Diphenoquinones  
 Abstract    Semiquinone radical anions are prototype compounds for contact ion pair formation with metal counter cations. In order to investigate the still open question whether bulky alkyl groups can sterically interfere, diphenoquinone derivatives 0 =C(RC=CH)2C=C(HC=CR)2C= 0 with R = C(CÜ3)3, CH(CH3)2 and CH3 have been selected and the following ESR/ENDOR results are obtained for the alkaline metal cations: The tetrakis(terr-butyl)-substituted radical anion only adds Li® and Na®, while K* forms no ion pair. The 3,3',5,5'-tetra(isopropyl)diphenoquinone radical anion is accessible to all cations Me®, although Rb® and Cs® seem to be present solvent-separated in solution. The tetramethyl-substituted radical anion unfortunately polyme­ rizes rapidly. Additional information concerns the ESR/ENDOR proof for ion triple radical cation formation [Li® M*e Li®]'®, or the difference in the coupling constants upon Me® docking at one 6e O=C group, suggesting that about 87% of the spin density is located in the cation-free molecular half of the diphenoquinone radical anion. Based on the wealth of ESR/ENDOR information, crystallization of the contact ion pairs and their structural characte­ rization should be attempted. Ausgangspunkte: Darstellung und Molekül­ eigenschaften von Diphenochinonen 
  Reference    Z. Naturforsch. 50b, 1699—1716 (1995); eingegangen am 13. März 1995 
  Published    1995 
  Keywords    One-Electron Reduction of Diphenoquinones, Cyclovoltammetry, ESR/ENDOR Spectra, Contact Ion Pairs and Triples 
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 TEI-XML for    default:Reihe_B/50/ZNB-1995-50b-1699.pdf 
 Identifier    ZNB-1995-50b-1699 
 Volume    50 
2Author    H. Bock, C. Arad, C. Näther, I. G. Öbel, A. John, R. BaurRequires cookie*
 Title    Elektronentransfer und Kontaktionen-Bildung, 45 [1, 2] Strukturänderungen bei der Einelektronen-Reduktion von Tetraphenyl- butatrien zum Radikalanion und bei der Zweifach-Deprotonierung von Tetraphenyl-butin-2 zum Tetraphenylbutatrien-Dianion Electron Transfer and Contact Ion Pair Form ation, 45 [1 ,2 ] Structural Changes on Single Electron R eduction of Tetraphenylbutatriene to its Radical A nion and on Twofold D eprotonation of Tetraphenylbutyne-2 to the Tetraphenylbutatriene D ianion  
 Abstract    Tetraphenylbutatriene is reduced under aprotic conditions to its ESR/ENDOR-spectro-scopically characterized radical anion and to its dianion, with both electron transfers quasi-reversible according to cyclovoltammetric measurements. The alkali cation salts, the red con­ tact ion pair [(H ^C ^C j K N a^H iC O C H iC H iO C H ^d and the dark violet contact ion triple [(H3C6)4C4" ' KLi^H ^CO CH iCIU O CH O ?^ can be prepared by single electron reduction at a sodium metal mirror or by twofold de-protonation of l,l,4,4-tetraphenylbutyne-2 using lithium-/;-butyl. Their single crystal structures as well as that of the parent acetylene have been determined at low temperatures. The essential structural changes observed are the twisting of both molecular halves (H5C6)2CC relative to each other with increasing negative charge. The simultaneously resulting bond alternancy >C = C = C = C< — >Ce -C = C -C < within the cumulene chain is discussed based on MNDO calculations for the structures determined. Ausgangspunkt: Die Strukturen von K um ulenen 
  Reference    Z. Naturforsch. 51b, 1381—1390 (1996); eingegangen am 15. November 1995 
  Published    1996 
  Keywords    Tetraphenylbutatriene Radical Anion and Dianion Salts, Cyclovoltammetry, ESR/ENDOR Spectra, Single Crystal Structures 
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 TEI-XML for    default:Reihe_B/51/ZNB-1996-51b-1381.pdf 
 Identifier    ZNB-1996-51b-1381 
 Volume    51