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  • 1
    Electronic Resource
    Electronic Resource
    Non-Concerted Cope Rearrangement (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 961-967 
    Details
    ISSN: 1434-193X
    Keywords: Diradicals ; Dioxygen trapping ; Diradical well ; Heat of formation ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The observation of practically identical activation parameters for the Cope rearrangement 2 → 6 and its “frustrated” counterpart 1 → 5 indicates a two-step mechanism for the reaction 2 → 6. Direct proof of this interpretation comes from trapping experiments, which demonstrate the intermediate formation of the diradicals 5 and 9. From the temperature and oxygen dependences of the trapping rates, recombination barriers of ΔH≠ = 11.5 and 6.5 kcal · mol-1 have been derived for 5 → 1 and 9 → 6, respectively. These results agree well with ab initio calculations (CASPT2).
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Thermochemistry of 7,7-Difluoro-2,7-toluenediyl (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1983-1986 
    Details
    ISSN: 1434-193X
    Keywords: Radicals ; Dioxygen trapping ; Radical reactions ; Singlet-triplet splitting ; Thermochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---From the oxygen and temperature dependence of the trapping rate of 7,7-difluorobenzocyclopropene (1) in the range 180-240 °C, the energy profile of the equilibrium 1 →←2 has been obtained. From the heat of hydrogenation of 1, its heat of formation is derived (ΔHof = +3.8 kcal·mol-1), as a result of which the heat of formation of the singlet state of the diradical 2 is estimated as 25.7 kcal·mol-1. Whereas the trapping experiments demonstrate unambiguously a triplet ground state for 2, only a lower limit for the singlet-triplet splitting (〉 6 kcal·mol-1) can be given.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Diradical Wells, IX. Stereochemistry of Cyclopropane Ring Opening: The Case of 1,1-Difluoro-2,3-diphenylcyclopropane (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1323-1327 
    Details
    ISSN: 0947-3440
    Keywords: Diradicals ; Dioxygen trapping ; Diradical well ; Supercritical fluids ; Radicals ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From the O2-dependence of the trapping rate of 1,1-difluoro-2,3-diphenylcyclopropane in supercritical CO2 in the temperature range 110-180°C and the rates of its geometrical isomerization and racemization of the trans-isomer, the energy profile for the geometrical isomerization is derived. Assuming that 7 is a common intermediate, the temperature dependence of the ratio of the rates of isomerization/racemization leads to a lowering of 1.2 kcal · mol-1 for the activation energy for the disrotatory cyclization of the intermediate diradical compared to the conrotatory mode. The energy barriers associated with cyclization of the diradical amount to 2.1 and 0.9 kcal · mol-1, respectively.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970707
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    Paper (German National Licenses)
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