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  • 1
    Electronic Resource
    Electronic Resource
    Sauerstoff-Abfang von Radikalen in überkritischem Kohlendioxid; Bildungsenthalpie und Rekombinationsbarriere des Cycloheptatrienyl-Radikals (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1679-1690 
    Details
    ISSN: 0947-3440
    Keywords: Oxygen trapping ; Radical recombination barrier ; Radical stabilization energy ; Tropenyl-oxygen equilibrium ; Supercritical fluid reactions ; Alkylperoxy bond strengths ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxygen Trapping of Radicals in Supercritical Carbon Dioxide; Heat of Formation and Recombination Barrier of the Cycloheptatrienyl RadicalThe homolytic thermal cleavage of bitropenyl (1) in supercritical carbon dioxide has been measured in the presence of 1 to 180 bar oxygen between 120 and 170°C. From these data the activation parameters of the dissociation and recombination reaction are derived, which lead to a heat of formation for the tropenyl radical (2) of ΔHfo = 64.7 kcal · mol-1. By using this value a radical stabilization energy (RSE) or 31.5 kcal · mol-1 is obtained, which differs by 1.7 kcal · mol-1 from the planar, acyclic isomer (trans,trans-1,3,6-trien-5-yl: RSE = 29.8 kcal · mol-1), which is practically equivalent to the relief of ring strain due to the formation of the radical. In agreement with the observed stability of 2 the equilibrium constant for its reaction with oxygen at 143°C is Keq = 727.7 mol-1, which corresponds to a bond strengths of 31.5 kcal · mol-1 for R-O2·. The equipment and the method used for these experiments are described in detail.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961029
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  • 2
    Electronic Resource
    Electronic Resource
    Bildungsenthalpie und Stabilisierungsenergie des Pentamethylcyclopentadienyl-Radikals (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1119-1122 
    Details
    ISSN: 0947-3440
    Keywords: Oxygen trapping ; Heat of formation ; Radical stabilization energy ; Supercritical fluid reactions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heat of Formation and Stabilization Energy of the Pentamethylcyclopentadienyl RadicalFrom the thermolysis of 1 in the presence of 1-60 bar oxygen between 70 and 100°C the activation energy for its dissociation is found to be 27.9 kcal · mol-1. Combining this result with the enthalpy of formation of 4 and a forcefield value for 1 leads to DH° (Me5C5-H) = 74.1 kcal · mol-1 and ΔHf0 (2) = 16.1 kcal · mol-1, which differs by 5.4 kcal · mol-1 from a value published recently by Walton[1]. The low dissociation enthalpy of 1 is caused only by the relieve of 28 kcal · mol-1 of strain. With an intrinsic radical stabilization energy (IRSE) of 17.3 kcal · mol-1 for 2 there is no justification for an extra stabilization due to cyclic conjugation.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199506151
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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
    van-der-Waals-Komplexe, Intermediate monomolekularer Reaktionen (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1917-1928 
    Details
    ISSN: 0947-3440
    Keywords: Diradicals ; Supercritical fluid reactions ; O2 trapping ; Reaction force field ; Cage effect ; Cope reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: van der Waals Complexes, Intermediates in Unimolecular ReactionsThermolysis of rac- and meso-1,1′,2,2′,3,3′ -hexamethyl-1,1′-biindenyl and (1E, 5E)-1,3,4,6-tetraphenyl-1,5-hexadiene in supercritical CO2 in the presence of oxygen allows to identify three types of intermediates, the free radicals (2 and 5) and the equilibrating complexes I and II consisting of radical pairs. From the oxygen dependence of the trapping and rearrangement rates it is shown, that the complex I is the primary thermolysis product, which in contrast to the complex II does not react with oxygen. The temperature dependance of these rates allows to calculate the enthalpy well of the complex II, which agrees well with predictions of our reaction force field.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961128
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