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  • 1
    Electronic Resource
    Electronic Resource
    Nichtkonzertierte Cope-Umlagerung? 1,2,6,7-Cyclodecatetraen-Thermolyse (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 739-749 
    Details
    ISSN: 0009-2940
    Keywords: Cope rearrangement ; Diradicals ; Oxygen trapping ; Energy well ; Chemical activation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nonconcerted Cope-Rearrangement? 1,2,6,7-Cyclodecatetraene ThermolysisFrom the pressure and oxygen dependence of the trapping rate a two-step mechanism for the Cope rearrangement of the title compound is deduced, its energy profile established, and the heat of formation of the intermediate diradical 3 determined. In contrast to the meso compound the rearrangement of the rac isomer proceeds by two competing processes, a concerted and a nonconcerted pathway. The different behavior of the meso and rac compound can be correlated to the boat and chair geometry of the respective transition states.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250330
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  • 2
    Electronic Resource
    Electronic Resource
    1,3,5-Cyclohexatrien-1,4-diyl und 2,4-Cyclohexadien-1,4-diyl (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1765-1779 
    Details
    ISSN: 0009-2940
    Keywords: Diradicals ; NO and O2 trapping ; Heat of formation ; Energy well ; Rearrangments ; Bergman cyclisation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Energy Well of Diradicals, V[1].  -  1,3,5-Cyclohexatriene-1,4-diyl and 2,4-Cyclohexadiene-1,4-diylThe energy profile of the Bergman rearrangement of (Z)-3-hexene-1,5-diyne (4) has been established from the NO and oxygen dependance of the trapping rate of the intermediate diradical 1 which leads to a heat of formation for 1,4-didehy-drobenzene (1) of δHOf= 138.0 ± 1.0 kcal . morl-1. By the same technique the heat of formation of 1,2,4-cyclohexatriene (2), generated by thermolysis of (Z)-1,3-hexadien-5-yne (10), gives δHOf = 105.1 ± 1.0 kcal . mol-1 which indicates a high diradical character for 2.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270929
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  • 3
    Electronic Resource
    Electronic Resource
    Zur Energiedelle des orthogonalen Trimethylenmethans. - 1-Methylen-2-phenylcyclopropan-Thermolyse (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 2717-2725 
    Details
    ISSN: 0009-2940
    Keywords: Diradicals ; Oxygen trapping ; Energy well ; Heat of formation ; Heat of hydrogenation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Energy Well of the Orthogonal Trimethylenemethane. - 1-Methylene-2-phenylcyclopropane ThermolysisFrom the heat of hydrogenation of 5, the activation enthalpy for the racemization of the title compound, and the oxygen dependance of the trapping rate of the intermediate diradical 8 the energy profile for the degenerate methylene-cyclopropane rearrangement can be constructed, which leads to heats of formation for the triplet and singlet state of the diradical 8 of ΔHf0 · 93.9 and 95.6 kcal mol-1, respectively.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931261222
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  • 4
    Electronic Resource
    Electronic Resource
    Bestimmung der Singulett-Triplett-Aufspaltung von Diradikalen mit Hilfe der Sauerstoff-Abfang-Technik (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 2047-2051 
    Details
    ISSN: 0009-2940
    Keywords: Diradicals ; Gas-phase kinetics ; Oxygen-trapping technique ; Singlet-triplet splitting ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Determination of the Singlet-Triplet Splitting of Diradicals by Oxygen-TrappingThe diradical 2, generated by thermolysis of 7-methylenebi-cyclo[3.2.0]hept-1-ene (1), can be trapped by oxygen in the gasphase. From the different trapping rates with and without added SF6 the intersystem crossing rates of the diradical have been deduced. From their temperature dependance the singlet-triplet splitting is calculated to be 7.4 kcal mol-1 with the triplet being the ground state. The triplet is protected by an enthalpy barrier of 13.0 kcal mol-1 against recombination of the unpaired electrons (2-tr→1). From the heat of hydrogenation of 1 the heat of formation of 1, 2-s and 2-tr is derived.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240928
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  • 5
    Electronic Resource
    Electronic Resource
    Zur Energie-Delle von Diradikalen; III1) 2,3,5,6-Tetramethylen-1,4-cyclohexadiyl (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 2751-2760 
    Details
    ISSN: 0009-2940
    Keywords: Diradicals ; Oxygen trapping ; Shock-tube technique ; Heats of formation ; Heats of hydrogenation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Energy Well of Diradicals, III1). - 2,3,5,6-Tetramethylene-1,4-cyclohexadiylGasphase thermolysis of ketone 1 leads to title diradical 3, which in the presence of oxygen yields 5 and peroxides. Assuming that the trapping reaction is collision-controlled, from the temperature dependence of the competing processes an activation enthalpy of 23 kcal/mol is derived for the recombination of the diradical. By the same technique starting from 5 the heat of formation of the diradical has been determined, ΔH°f(g)=100.8 kcal/mol.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911241218
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  • 6
    Electronic Resource
    Electronic Resource
    Zum konzertierten oder nichtkonzertierten Verlauf von Reaktionen; Thermolyse von Dispiro[2.2.2.2]deca-4,9-dien (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1361-1366 
    Details
    ISSN: 0947-3440
    Keywords: Diradicals ; Oxygen trapping ; Energy well ; Supercritic fluid reactions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Concerted and Nonconcerted Reaction Path; Thermolysis of Dispiro[2.2.2.2]deca-4,9-dieneThe enthalpy profile for the equilibrium 1 ⇄ 2 ⇄ 3 has been determined by oxygen trapping. From the oxygen dependence at low (0.0005-0.2 bar) and high pressure (1-180 bar) between 130 and 190°C the enthalpy wells of the diradicals 3 and 2 have been derived (3 17.1, 2 3.7 kcal · mol-1). The observation of a nonconcerted path for the equilibrium 1 ⇄ 3 is important with respect to the understanding of the controlling factor of the concerted and nonconcerted path of a reaction. The existence of a favourable potential energy path obviously is not of prime importance.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507181
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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Die Allen-Racemisierung, eine zweistufige Reaktion (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 2171-2183 
    Details
    ISSN: 0947-3440
    Keywords: Diradicals ; Gas-phase kinetics ; NO and O2, trapping ; Racemization barrier ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Racemization of Allene, a Two-Step ReactionFor four vinyl- and phenyl-substituted allenes racemization enthalpies have been determined, which are 2-6 kcal · mol-1 below the estimate derived from the parent system by correction for the additional radical stabilization of the intermediate allyldiradical 2(I), indicating the growing importance of the carbene type structure 2(II) for the intermediate.  -  The racemization of 1,3-dimethylallene 1b at temperatures 〉300°C in the presence of NO allows the trapping of an intermediate, which is considered to be the orthogonal allyl diradical 2b. From the trapping kinetics (307-388°C), the reversible bimolecular addition of NO at low temperatures (225-285°C) and the strength of the C—NO bond an enthalpy well for the singlet diradical of 2.7 kcal · mol-1 and a singlet-triplet splitting of 5.6 kcal · mol-1 is derived with the triplet being the groundstate.  -  The postulated intermediate diradical 2 can be stabilized electronically by phenyl and vinyl groups or by strain when incorporated in an eight-membered ring. Thermolyses of the optically active 1,2,5-cyclooctatriene 18 in the presence of oxygen allows to determine the enthalpy well of the corresponding diradical 25 to be 13.1 kcal · mol-1.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961231
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  • 10
    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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