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  • 1
    Electronic Resource
    Electronic Resource
    1,4-Didehydronaphthalin (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1691-1695 
    Details
    ISSN: 0947-3440
    Keywords: Diradicals ; NO trapping ; Diradical well ; Heat of formation ; Bergman cyclization ; Hydrogen abstraction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,4-DidehydronaphthaleneThe energy profile of the Bergman equilibrium o-diethinyl-benzene (1 · 1,4-didehydronaphthalene (2) has been established from the temperature and NO dependence of the trapping rate of the diradicals 2 which leads to a heat of formation for 2 of ΔHf0 = 152.9 · 1.4 kcal · mol-1. Activation parameters for the hydrogen abstraction of 2 and 1,4-didehydrobenzene (5) have been derived from the rate of the naphthalene and benzene formation, when 1 and cis-3-hexene-1,5-diyne (4) are heated in the presence of methanol, toluene, and 1,4-cyclohexadiene.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961030
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  • 2
    Electronic Resource
    Electronic Resource
    Resonanzenergie von Diradikalen  -  1,8-Naphthoquinodimethan (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 2155-2169 
    Details
    ISSN: 0947-3440
    Keywords: Diradicals ; NO Trapping ; O2 Trapping ; Trapping, NO and O2 ; Energy well ; Singlet-triplet splitting ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Resonance Energy of Diradicals.  -  1,8-NaphthoquinodimethaneFrom the racemization of 19c and the temperature and NO dependence of the trapping rate of 20b between 218 and 288°C the energy profile for the equilibrium 19b ⇄ 20b is derived. The singlet-triplet splitting of the diradical is 2.5 kcal · mol-1 with the triplet being the ground state. By comparison of the experimental reaction enthalpy with the analogous value for 25, 26 or a hypothetical model reaction with non-interacting radicals it is shown that the stabilizing interaction of the radicals in the singlet state of 20b is negligible making the stabilization of the triplet equivalent to the singlet-triplet splitting. By using literature data it is shown by an analogous analysis that the interaction of the radicals in the bisallyl diradical 28 and in the triplet state of the trimethylenmethane derivative 29 is also negligible whereas in the singlet state of 29 the interaction is strongly destabilizing.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961230
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Zur Rekombinationsenthalpie von Radikalen  -  Thermochemie der Ringöffnung von Cyclophanen (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 2141-2154 
    Details
    ISSN: 0947-3440
    Keywords: Diradicals ; Gasphase kinetics ; Trapping, NO and O2 ; Supercritical fluid reactions ; Reaction forcefield ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical Recombination Enthalpy.  -  Thermochemistry of the Ringopening of CyclophanesBy thermolysis of the cyclophanes 1, 5, 8, 11, 14, 18, and 21 in the presence of NO or O2 the enthalpy profiles for the ring opening were determined from the temperature, NO, or O2 dependance of the trapping rates of the intermediate diradicals. The experimental enthalpy wells, which varied between 3 and 12 kcal · mol-1, can be simulated well with a reaction forcefield making use of the EVBH method of Malrieu et al. This result gives confidence that also meaningful recombination barriers of radicals can be obtained by this method.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961229
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  • 4
    Electronic Resource
    Electronic Resource
    Bicyclo[4.4.0]deca-1,6-diene-2,7-diyl: A 1,4-Didehydrobutadiene Derivative (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1329-1331 
    Details
    ISSN: 0947-3440
    Keywords: Diradicals ; NO- and O2-trapping ; Diradical well ; Heats of formation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From the NO- and O2-dependence of the trapping rate of 1,6-cyclodecadiyne (3) in the gas phase and in supercritical CO2 in the temperature range 160-290°C, the enthalpy profile for the equilibrium 3 ⇌ 4 has been established. For the diradical 4, a heat of formation of 116.2 kcal · mol-1 is obtained, which agrees well with the expectation value derived by the abstraction of two hydrogen atoms from hexahydronaphthalene (5).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970708
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  • 5
    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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