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1982 (1)
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1980 (1)
1Author    Gernot Frenking, Jochen Schmidt, Helmut SchwarzRequires cookie*
 Title    MNDO-Rechnungen zur unimolekularen CO-Abspaltung aus Isomeren C3H5CO + -Ionen MNDO Calculations on the Unimolecular CO Loss from Isomerie C3HsC0 + Ions  
 Abstract    In agreement with experimental results MNDO calculations indicate that unimolecular CO loss from the isomeric ions CH2 = CHCH2-CO+ (1), C-C3H5-CO+ (2), and CHsCH = CH-CO + (3), gives exclusively allyl cation (4). It is shown that, whereas CO loss from 1 is a continuously endothermic process, the analogous reaction from 2 and 3 follows relatively complicated pathways. For 2, the energetically most feasible reaction involves an isomerization of 2 to 1 via the intermediate a-oxo-and /?-oxocyclobutyl cations (8) and (9). This reaction sequence is 10 kcal • mol -1 lower in energy than direct CO loss from 2 coupled with isomerization of the incipient cyclopropyl cation (7) to allyl cation (4). For 3 it is shown that this ion undergoes isomerization to 2 prior to CO loss. The alternative reaction, i.e. direct CO elimination giving rise to 1-propenyl cation (11) or isomerization to 1 were 35 and 43 kcal • mol -1 higher in energy than the process 3 -* • 2. 
  Reference    Z. Naturforsch. 35b, 1031—1034 (1980); eingegangen am 21. März 1980 
  Published    1980 
  Keywords    Carbocation Chemistry, Quantum Mechanical Calculations, Potential Energy Surfaces 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-1031.pdf 
 Identifier    ZNB-1980-35b-1031 
 Volume    35 
2Author    Herman Teeninga, WimC. Nieuwpoort, JanB F N EngbertsRequires cookie*
 Title    Sulfonamidyls, 4. Ab Initio MO Calculations on Sulfonyl and Carbonyl Substituted Aminyl Radicals  
 Abstract    The relative magnitude of the nitrogen hyper-fine splitting constants of sulfonamidyls and carboxamidyls is rationalized in terms of the results of ab initio MO calculations using the "double zeta" basis set of Roos and Siegbahn. 
  Reference    Z. Naturforsch. 36b, 279—281 (1981); received October 6 1980 
  Published    1981 
  Keywords    Sulfonamidyls, Carboxamidyls, ESR Spectra, Quantum Mechanical Calculations 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-0279_n.pdf 
 Identifier    ZNB-1981-36b-0279_n 
 Volume    36 
3Author    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 
4Author    Gernot Frenking, Helmut SchwarzRequires cookie*
 Title    Frontorbitale und 1.2-Hydridwanderungen in Carbeniumionen Frontier Orbitals and 1,2-Hydrogen Shifts in Carbenium Ions  
 Abstract    For various carbenium ions it is shown that the energy value and the degree of localiza-tion of the LUMO have a significant influence on the energy barriers of 1,2-hydrogen shifts. The structures of the transition states are in line with the Hammond-Postulate. 
  Reference    Z. Naturforsch. 36b, 797—801 (1981); eingegangen am 10. März 1981 
  Published    1981 
  Keywords    Carbocation Chemistry, 1, 2-Hydrogen Migration, Frontier Orbitals, Quantum Mechanical Calculations, Transition States 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-0797.pdf 
 Identifier    ZNB-1981-36b-0797 
 Volume    36