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1982 (2)
1Author    Roland Wolfschütz, Wilfried Franke, Nikolaus Heinrich, Helmut Schwarz, Wolfgang Blum, WilhelmJ. RichterRequires cookie*
 Title    Eliminierung von Aceton und Bildung von protoniertem Aceton bei der chemischen Ionisation von []-Tetramethylcyclohexanon Elimination of Acetone and Formation of Protonated Acetone from [2,2,6,6]-Tetramethylcyclohexanone under the Condition of Chemical Ionisation  
 Abstract    By means of appropriately D and 13 C labelled precursors it is shown that the proton catalysed degradation of [2,2,6,6]-tetramethyl cyclohexanone {e.g. elimination of acetone and formation of protonatecl acetone from [MH]+) proceeds via two distinct pathways. The energetically favoured one (pathway A, Scheme 1) involves a sequence of [l,2]-methyl migration, ring contraction and methyl migration, whereas the energetically less attractive path B commences with a Wagner-Meerwein ring contraction, followed by hydroxyl and methyl migration. Semi-empirical quantum mechanical calculations (MNDO) are em-ployed to explore computationally relevant parts of the potential energy surface. The syntheses of the specifically 13 C labelled title compounds (1 a, b) are described in detail. 
  Reference    Z. Naturforsch. 37b, 1169—1173 (1982); eingegangen am 19. März 1982 
  Published    1982 
  Keywords    Wagner-Meerwein Rearrangement, Mass Spectra, Potential Energy Surface Calculations 
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 TEI-XML for    default:Reihe_B/37/ZNB-1982-37b-1169.pdf 
 Identifier    ZNB-1982-37b-1169 
 Volume    37 
2Author    Z. NaturforschRequires cookie*
 Title    Herrn  
 Abstract    Water loss from protonated gaseous 1-decalon and 8a-methyl-l-decalon under the condition of chemical ionisation mass spectrometry proceeds via at least three distinct pathways, all of which commences with a [1.2]-hydrogen or [1.2]-methyl migration, thus giving rise to the formation of the central intermediate 10. H20 loss from 10 proceeds either directly, involving a hydrogen from the position (C-4 a) (Scheme 3; pathway 10 ->15 ->16), or from the rearranged ions 17 and/or 20. The fact that eis-and trans-8a-methyl-l-decalones and their deuterated isotopomers behave essentially identical is explained by loss of the stereochemical integrity of the ring conjunction. The mechanistic features of this unusual process (Scheme 2) have been explored by semi-empirical MINDO/3 calculations for the model system 23 (Scheme 4). The calculations reveal that there are two competing pathways for CH3 migration, one involving a sequence of [1.2]-shifts (23 -^24 ->25 ->26->27), the other -being energetically less favoured -corresponds to a direct [1.3]-methyl migration (Scheme 6; 23 -^33 ->27), in which the methyl group migrates with retention of configuration. This process is symmetry forbidden. For the corresponding symmetry allowed [1.3]-methyl migration with inversion of configuration of the migrating group no pathway could be detected computationally. Both the experi-mental and theoretical investigations allow one to draw a detailed picture of H20 loss from protonated cyclic ketones in the gas phase. -The syntheses of the labelled substrates are described in detail. 
  Reference    Z. Naturforsch. 37b, 724—735 (1982); eingegangen am 23. Dezember 1981 
  Published    1982 
  Keywords    Protonated Ketones, Wagner-Meerwein Rearrangement, Quantum Mechanical Calculations, Potential Energy Surface Calculations 
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 TEI-XML for    default:Reihe_B/37/ZNB-1982-37b-0724.pdf 
 Identifier    ZNB-1982-37b-0724 
 Volume    37