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  • Dioxygen trapping  (3)
  • Calculations, force field  (2)
  • 1
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2349-2371 
    ISSN: 0009-2940
    Schlagwort(e): Atropisomers ; Inversion barrier ; Lineshape analysis ; Calculations, force field ; Resonance energy ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Inversion Barriers of ortho,ortho′-Bridged BiphenylsThe syntheses and spectroscopic properties of the ortho,ortho′-bridged biphenyls 2-19 are described. In the case of 5, 15, and 16 the inversion barrier is determined from the temperature dependence of the NMR spectra (lineshape analysis), in the case of 12, 13, and 14 from the temperature of coalescence, and in the case of 2a, 3b, 7, 17, 18, and 19 from the rate of racemization of the optically active compounds. The experimental inversion barriers, including data from the literature, are compared with those calculated using the extended force field (MM2erw). The conformational behavior of the title systems is significantly affected upon transformation into the corresponding dianion salts. The relevant energy terms are discussed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 1461-1470 
    ISSN: 0009-2940
    Schlagwort(e): Allyl stabilisation energy ; Calculations, force field ; Rotational barrier, intrinsic ; Gas-phase kinetics ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Rotational Barriers of Vinyl-Substituted OlefinesFor the vinyl-substituted olefines 1 - 14 activation parameters for the geometrical isomerisation have been determined in the gas-phase. By comparison of these barriers with the corresponding ones of the isolated double bonds, each corrected by the contribution of the steric energy to the ground and transition state, a value of 13.5 ± 1.1 kcal mol-1 for the allyl stabilisation energy (ASE), defined as replacement of alkyl by vinyl, has been derived.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 961-967 
    ISSN: 1434-193X
    Schlagwort(e): Diradicals ; Dioxygen trapping ; Diradical well ; Heat of formation ; Ab initio calculations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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).
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1323-1327 
    ISSN: 0947-3440
    Schlagwort(e): Diradicals ; Dioxygen trapping ; Diradical well ; Supercritical fluids ; Radicals ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Zusätzliches Material: 7 Tab.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1983-1986 
    ISSN: 1434-193X
    Schlagwort(e): Radicals ; Dioxygen trapping ; Radical reactions ; Singlet-triplet splitting ; Thermochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---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.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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