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1979 (2)
1Author    Heinz Falk, Klaus ThirringRequires cookie*
 Title    Beiträge zur Chemie der Pyrrolpigmente, XXXIII [1] Darstellung, Struktur und Eigenschaften von isomeren N-Methyl-Bilatrienen-abc (N-Methyl-etiobiliverdine-IV-y) On the Chemistry of Pyrrole Pigments, XXXIII [1] Synthesis, Structure and Properties of Isomeric N-Methyl-bilatrienes-abc (N-Methyl-etiobiliverdines-IV-y)  
 Abstract    Methylation of etiobiliverdin-IV-y yields a ring-A N-methylated product the structure of which was proven by comparison with the corresponding monolactimether and the ring-B methylated product which was synthesized on an independent route. The configura-tion (Z,Z,Z) was deduced by iH-NMR experiments and a more or less helical conformation which is most twisted at the ring-A methine fragment was found. Photoisomerization exclusively takes place at this position giving the (E,Z,Z) diastereomer, a reaction which is discussed in terms of the correlation of light absorption, methine single bond twist and photochemical selectivity. 
  Reference    Z. Naturforsch. 34b, 1448—1453 (1979); eingegangen am 25. Mai 1979 
  Published    1979 
  Keywords    UY-VIS, iH-NMR, Photoisomerization, Configuration, Conformation 
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 TEI-XML for    default:Reihe_B/34/ZNB-1979-34b-1448.pdf 
 Identifier    ZNB-1979-34b-1448 
 Volume    34 
2Author    Peter Brüggeller, Erwin MayerRequires cookie*
 Title    Dimethylhalonium-Ionen in Aluminiumhalogenid/Methylhalogenid-Lösungen Dimethylhalonium-Ions in Aluminium Halide/Methyl Halide Solutions  
 Abstract    Evidence for the formation of (CH3)2Br+ and (CH3)2l + in CH3Br and CH3I solutions saturated with AlBr3 comes from the appearance of a second singlet in the iH NMR spectrum. The (CH3)2Br+ ion is formed at —40 °C to about 5 mol%, the (CH3)2l + ion at —12 °C with 50 mol% yield. At higher temperatures the concentration of the halonium ions decreases rapidly. The (CH3)2Br+ ion is not detectable at room temperature, the concentra-tion of (CH3)2l + decreases to about 30 mol%. Dilution of the saturated solutions with methyl halide also reduces the halonium ion concentration. An AlBrs/CHsBr solution with a molar ratio of 1:3 at —40 °C shows no sign of (CH3)2Br+ formation in the X H NMR spectrum. Both effects are best explained by formation of dimethylhalonium ions from the adduct CH3X-AIX3 and by dependence of adduct concentration on temperature and dilution. Exchange of (CH3)2Br+ and (CH3)2l + with methyl halide is slow on the NMR time scale at low temperatures similar to the results in SbFs/SC^. The ] H NMR singlets of (CH3)2Br+ and (CH3)2l + are shifted to lower field by 1.32 and 1.68 ppm in comparison with the chemical shifts in SbFs/SC^ solution. 
  Reference    Z. Naturforsch. 34b, 896—899 (1979); eingegangen am 5. März 1979 
  Published    1979 
  Keywords    Dimethylbromonium Ion, Dimethyliodonium Ion, iH NMR, Aluminium Halides, Methyl Halides 
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 DEBUG INFO      
 TEI-XML for    default:Reihe_B/34/ZNB-1979-34b-0896.pdf 
 Identifier    ZNB-1979-34b-0896 
 Volume    34