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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
    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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  • 3
    Electronic Resource
    Electronic Resource
    Thermal Isomerisation of Substituted Semibullvalenes and Cyclooctatetraenes - A Kinetic Study (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 813-822 
    Details
    ISSN: 1434-193X
    Keywords: Cyclizations ; Hydrocarbons ; Isomerizations ; Kinetics ; Polycycles ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Whereas 1,5-dimethylsemibullvalene (1b) equilibrates with 1,5-dimethylcyclooctatetraene (2b), the semibullvalene-2,6-dicarbonitriles 13 rearrange irreversibly to afford mixtures of the isomeric cyclooctatetraene-1,5-dicarbonitriles 14 and 15. Arrhenius and Eyring parameters of these thermal isomerisation reactions have been determined for the gas phase (1b → 2b) and [D6]benzene solutions (1b → 2b, 13 → 14 + 15). Furthermore, the activation parameters of the known rearrangement of octamethylcyclooctatetraene (3) to octamethylsemibullvalene (4) have been determined. - The data for these compounds, together with those for related compounds previously reported in the literature, show that substituents not only influence the relative stabilities of the semibullvalene and cyclooctatetraene systems but also the height of the energy barrier for their interconversion. Those substituents that lower the barrier toward the degenerate Cope rearrangement of semibullvalenes simultaneously accelerate their rearrangement to cyclooctatetraenes thus limiting the thermal stability of the former.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Thermische Umlagerung von 2-Methylentricyclo [4.1.0.01,3] heptan (1973)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 85 (1973), S. 512-512 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19730851113
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  • 5
    Electronic Resource
    Electronic Resource
    Thermische Diastereomerisierung von 3-Methyl-6-äthylidenbicyclo[3.1.0]hexan; orthogonales versus planares Trimethylenmethan Diese Arbeit wurde von der Deutschen Forschungsgemeinschaft und dem Fonds der Chemischen Industrie unterstützt. (1975)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 87 (1975), S. 777-778 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19750872111
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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    The Barrier to Rotation about the Double Bond in Methylenecyclopropane (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 763-768 
    Details
    ISSN: 1434-193X
    Keywords: Pyramidalization ; Rotational barrier ; Strained molecules ; Propellanes ; Small-ring systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Activation parameters have been determined in the gas phase for the geometrical isomerization of the double bonds in two phenyl-substituted methylenecyclopropanes (2 and 8). Comparison with the analogous values for three sterically non-restricted styrene derivatives (15, 16 and 17) shows that the enthalpies of activation for the methylenecyclopropanes are lower by 3.7 kcal mol-1. This value, which is an upper limit to the amount of strain energy released by pyramidalization of the ring carbon atom in the orthogonal diradical transition state when undergoing geometrical isomerization, is considerably smaller than the value of 12-14 kcal mol-1 by which the strain energy of methylenecyclopropane is larger relative to that of cyclopropane. Our kinetics experiments thus show that the angle strain, associated with incorporating a trigonal carbon atom into the three-membered ring, is not responsible for the majority of the additional strain energy of methylenecyclopropane, relative to that of cyclopropane.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Non-Concerted Cope Rearrangement (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2941-2941 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In several instances the last name of one of the authors (U. E. H.) is misprinted; it should read as above. In Tables 4 and 5 the different k factors are misprinted (104 instead of 104 etc.).
    Type of Medium: Electronic Resource
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  • 10
    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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