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  • 1
    Electronic Resource
    Electronic Resource
    Geminal substituent effects, 11. The anomeric effect in orthoesters  -  the concept of geminal pairwise interactions for the interpretation of standard enthalpies of formationDedicated to Professor Rolf Huisgen on the occasion of his 75th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 2059-2067 
    Details
    ISSN: 0947-3440
    Keywords: Anomeric effect ; Enthalpies of formation ; Geminal substituents, energetic interaction of ; Increments, thermochemical, of orthoesters ; Group increments, interpretation of ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New enthalpies of formation ΔHf^(g) are provided for the series of orthoesters 2a-2f, 3 and 4 from their enthalpies of combustion ΔHc^ and their enthalpies of vaporization ΔHvap^ or enthalpies of sublimation ΔHsub^. From these data and from literature data the following new thermochemical increments were calculated [kJ · mol-1]: CH[O3] - 106.4, C[O3, C] -103.7, and C[O3, Ph] -124.5. In addition the increment C[O4] - 167.1 was calculated from literature data for ΔHf^(g) of the orthocarbonates 9a and 9b. The anomeric stabilization derived from these results and from previous results for acetals and ketals are reported in Table 3. - A new concept of additive structural increments for the quantitative analysis of the group increments of hydrocarbons, ethers, acetals, and ketals is proposed. It is shown that the increments for CH3, CH2, CH, and C groups with their different neighboring atoms (see Table 4) are determined by the number of hydrogen atoms in the group and by the number of pairwise geminal interactions between all atoms attached to the central carbon atom. - Using this procedure for orthoesters and orthocarbonates, deviations from additivity for the geminal interaction between oxygen atoms, i.e. the anomeric effect, are observed.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199512291
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  • 2
    Electronic Resource
    Electronic Resource
    Substituent effects on the C—C bond strength, 19Part 18: Ref.. Geminal substituent effects, 10Part 9: Ref.. Radical stabilization enthalpies of α,α-bis(methoxycarbonyl)alkyl and tris(methoxycarbonyl)methyl radicalsDedicated to Prof. Dr. P. v. R. Schleyer on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1483-1493 
    Details
    ISSN: 0947-3440
    Keywords: Enthalpies of formation ; Geminal substituents, energetic interaction of ; Bond cleavage, C-C, kinetics of ; Radicals, stabilization of ; Increments, thermochemical, of esters ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heats of formation ΔHf0(g) were determined from enthalpies of combustion ΔHf0(c) and enthalpies of vaporization ΔHvap0 or enthalpies of sublimation ΔHsub0 for the eight substituted methanetricarboxylates 2a-h. From these data and from previously determined enthalpies of formation Δf0 of substituted malonic esters new thermochemical group increments were derived. From these increments and from the recently published improved increments for carboxylic acid esters the gem. interaction enthalpies of two and three COOR groups were calculated. The radical stabilization enthalpies RSE of α,α-bis(methoxycarbonyl)alkyl (18.2 kJ mol-1, 1a) and tris-(methoxycarbonyl)methyl radicals (5.2 kJ mol-1, 1b) were derived from kinetic data obtained by means of our previously developed protocol. They were corrected for the gem. interaction energies of the ester groups in the ground state and are satisfactorily explained by an additive stabilizing effect of the ester substituents and by dipolar substituent interactions in the radicals. The dipolar energies were taken from MM2 calculations.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199508203
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  • 3
    Electronic Resource
    Electronic Resource
    New Hydrogen Transfer Catalysts (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2219-2230 
    Details
    ISSN: 1434-193X
    Keywords: Retrodisproportionation ; Arenes ; EPR spectroscopy ; Thermochemistry ; Coal liquefaction ; Catalysis ; Hydrogen transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transfer of hydrogen from excess 9,10-dihydroanthracene (DHA) to acceptors such as α-methylstyrene is catalyzed, i.e. occurs at temperatures in the range 200-260 °C instead of 280-320 °C, when hydrocarbons with weaker C-H bonds than DHA, e.g. 6H-benzo[cd]pyrene (4), 7H-dibenzo[a,kl]anthracene (5), 4-methyl-7H-benzo[de]naphthacene (6) or 8H-dibenzo[b,fg]pyrene (7), are added to the reaction mixture. The reactions are initiated by bimolecular H-atom transfer from 4-7 to the acceptor (retrodisproportionation) and proceed by nonchain radical mechanisms. This is supported by isotopic labelling and kinetic isotope effects, substituent and solvent effects, EPR spectroscopy of intermediate radicals, and by a comparison of the thermochemical and kinetic characteristics of these reactions.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Uncatalyzed Transfer Hydrogenation and Transfer Hydrogenolysis: Two Novel Types of Hydrogen-Transfer ReactionsDedicated to Professor Paul D. Bartlett on the occasion of his 90th birthday (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 1406-1430 
    Details
    ISSN: 0570-0833
    Keywords: arenes ; coal liquefaction ; hydrogenations ; radical reactions ; reaction mechanisms ; Arenes ; Coal liquefaction ; Hydrogenation ; Radical reactions ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Uncatalyzed transfer hydrogenations are H2-transfer reactions in which donors that contain weakly bound hydrogen atoms undergo an H-atom transfer (retrodisproportionation) onto an acceptor containing unsaturated bonds such as C=C, C=O, C=N, N=N, N=O. Transfer hydrogenolyses are reactions in which σ bonds are cleaved upon additon of H2. These hydrogenations are terminated by H, transfer; they do not follow a radical-chain mechanism. The initial steps of both types of reactions, H-atom transfer, complement the bimolecular formation of 1,4-diradicals from alkenes or heteroalkenes within the scope of bimolecular radical formation (Molecule-Induced Radical Formation, MIRF). The title reactions play an important role in coal liquefaction, aromatization reactions with nitroarenes or quinones, and possibly biochemical dehydrogenations. This review focuses on mechanistic studies, structure-reactivity relationships, and current applications of these reactions.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199714061
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