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  • 1
    Electronic Resource
    Electronic Resource
    Substituenteneffekte auf die C—C-Bindungsstärke, 14. Kinetische und thermodynamische Stabilität von 2,3-Bis(dialkylamino)-1,4-diketonen  -  Stabilisierungsenergie capto-dativ substituierter a-Dialkylamino-a-Carbonylalkyl-RadikaleProf. Dr. H.-G. Viehe zum 65. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 697-710 
    Details
    ISSN: 0009-2940
    Keywords: C—C Bond cleavage, kinetics of ; Heats of formation ; Radicals, stability of ; Capto-dative effect ; Geminal substituents, energetic interaction of ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituent Effects on the Strength of C—C Bonds, 14[1].  -  Kinetic and Thermodynamic Stability of 2,3-Bis(dialkylamino)-1,4-diketones  -  Energy of Stabilization of α-Dialkylamino α-Carbonylalkyl Radicals with Capto-dative SubstituentsProf. Dr. H.-G. Viehe zum 65. Geburtstag gewidmet.The equilibrium constants and rate constants for the dissociation of the 2,3-bis(dialkylamino)-1,4-diketone diastereomers meso- and DL-7a and 7b were measured over a temperature range of 40°C. From the enthalpies of dissociation ΔHDiss and enthalpies of activation ΔH≠ and the strain enthalpies of 7 the bond dissociation enthalpies BDE(C—C) of 7 were determined. By comparison with the dissociation enthalpies of Ct-Ct alkanes[21] the change of these BDEs(C—C) by the cap-to-dative substitution was determined to be 85.4 kJ mol-1 (20.4 kcal mol-1). The heats of formation ΔHof (g) of a series of amino ketones 8 were determined from their heats of combustion and their heats of evaporation. From the ΔHof(g) values in combination with MM2 calculations of their strain enthalpies strain-free increments CHn[N, CO, C2 - n] with n With n = 0, 1, 2 were derived and geminal interaction enthalpies in the ground states were obtained thereof. The radical stabilization enthalpy RSE of 6 was deduced from the ΔBDE(C—C) values and the ground state effect to be 73.6 kJ mol-1 (17.6 kcal mol-1). From these data and the radical stabilization enthalpies RSE of α-aminoalkyl radicals (4.2 kJ mol-1) and α-carbonyl radicals (28.9 kJ mol-1) a synergetic radical stabilization enthalpy of 40.5 kJ mol-1 (9.7 kcal mol-1) is deduced. This number combines “extra” resonance stabilization and general inductive or anomeric geminal substituent interaction in the radicals. The crystal structure of meso-7a has been determined by X-ray diffraction methods.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270420
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  • 2
    Electronic Resource
    Electronic Resource
    Thermolabile Hydrocarbons, 33. Thermochemistry and Thermal Decomposition of 9,9′-Bifluorenyl and 9,9′-Dimethyl-9,9′-bifluorenyl - The Stabilization Energy of 9-Fluorenyl Radicals (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1095-1103 
    Details
    ISSN: 0009-2940
    Keywords: Heats of formation ; Bond cleavage ; C—C ; kinetics of ; Radicals ; stability of ; Correlation between heats of vaporization and solvent-accessible surfaces ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From thermochemical measurements the heats of formation ΔH0f(g) forfluorene (1), 9-methylfluorene (2), 9,9′-bifluorenyl (5), and 9,9′-dimethyl-9,9′-bifluorenyl (6) were determined. The homolytic cleavage of the dimers 5 and 6 to 9-fluorenyl (3) and 9-methyl-9-fluorenyl radicals (4), respectively, was studied in mesitylene with thiophenol as trapping agent and found to follow first-order kinetics. The activation parameters ΔH≠(5) = 212.6 (±2.1) kJ mol-1, ΔS≠(5) = 70.3 (±4.2) J mol-1 K-1 ΔH≠(6) = 164.9 (±0.7) kJ mol-1, and ΔS≠(6) = 88.2 (±1.9) J mol-1 K-1 were obtained. For 3 and 4 the radical stabilization energies RSE(3) = 67 (±7) kJ mol-1 (relative to isopropyl) and RSE(4) = 64 (±8) kJ mol-1 (relative to tert-butyl) were determined by a comparison with the activation parameters of the thermolysis of alkanes possessing the same strain enthalpy. The heats of formation for 3 and 4 and the C-H bond dissociation energies for the C-H bond in the 9-position of 1 and 2 were determined to be ΔH0f(g,3) = 300 kJ mol-1, Δ0f(g,4) = 268 kJ mol-1, BDEC—H(1) = 343 and BDEC—H(2) = 338 kJ mol-1 (estimated errors correspond to those of the RSE values). A good correlation between the heats of vaporization of 37 aromatic hydrocarbons and their calculated solvent-accessible surfaces was demonstrated. Hence, a new method to estimate heats of vaporization was established.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270619
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  • 3
    Electronic Resource
    Electronic Resource
    Thermolabile hydrocarbons, 34. Part 33: Ref.[1a].. Kinetics of the generation of 1,3-di-tert-butylallyl radicals by thermal CC bond cleavage reactions (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 515-522 
    Details
    ISSN: 0947-3440
    Keywords: Bond cleavage, C-C, kinetics of ; Allyl radicals, stability of ; Calculations, molecular mechanics ; Enthalpies of formation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title radicals were generated by thermal decomposition of (E,E)-meso- and (E,E)-(±)-5,6-di-tert-butyl-2,2,9,9-tetramethyl-3,7-decadiene (4a, b), (E)-5-(1,1-dimethylethyl)-2,2,6-trimethyl-6-phenyl-3-heptene (6), and (E)-5-(diphenyl-methyl)-2,2,6,6-tetramethyl-3-heptene (7). The activation parameters of these reactions were calculated from the rate constants which were followed over a 40°C temperature range. The enthalpies of formation of 4a, b were determined from the enthalpies of combustion and enthalpies of vaporization, those of 6 and 7 by MM2 calculation. From these data and their comparison with those of comparable saturated hydrocarbons of similar strain the radical stabilization enthalpy of the title radical RSE = 11.4 ± 1.5 kcal/mol was determined, which is in good agreement with results obtained from other model compounds (12.6 kcal/mol) previously.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950371
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  • 4
    Electronic Resource
    Electronic Resource
    Substituenteneffekte auf die C—C-Bindungsstärke, 16. Thermische Stabilität und Bildungsenthalpie von β-Dicarbonylverbindungen.  -  Stabilisierung von α,α′-Diketoalkyl-Radikalen (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 41-51 
    Details
    ISSN: 0947-3440
    Keywords: Enthalpies of formation ; Geminal substituents, energetic interaction of ; Bond cleavage, C—C, kinetics of ; Radicals, stability of ; Increments, thermochemical ; Bond strength, substituent effects on ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituent Effects on the CC Bond Strength, 16.  -  Thermal Stability and Enthalpies of Formation of β-Dicarbonyl Compounds.  -  Stabilisation Enthalpies of α,α′-Diketoalkyl RadicalsThe geminal interactions of the two carbonyl groups in seven β-diketones of the type 8-9 and 11-13 were estimated from their enthalpies of formation, which were deduced from their heats of combustion and enthalpies of vaporization. The radical stabilisation enthalpies RSE of the α,α′-diketoalkyl radicals 9-13 were obtained from the enthalpies of activation ΔH≠ of thermal CC bond cleavage of eight model compounds of the type 9-13 by their comparison with ΔH≠ of comparable hydrocarbons of similar strain. For non-cyclic α,α′-diacyl-alkyl radicals and six-membered cyclic ones RSE = 54.8 ± 1.3 kJ mol-1 was determined, which indicates an additive stabilisation by two carbonyl groups.
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950108
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