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  • 1
    Electronic Resource
    Electronic Resource
    Thermolabile Kohlenwasserstoffe, 32. Konkurrierende Cope-;Umlagerung und Homolyse von meso- und DL-3,4-Di(1-cyclohexen-1-yl)-2,2,5,5-tetramethylhexan (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 117-127 
    Details
    ISSN: 0009-2940
    Keywords: Radical stabilization, allylic ; Cope rearrangement ; C  -  C Bond cleavage ; Thermochemistry ; Kinetics ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermolabile Hydrocarbons, 32.  -  Competing Cope-;Rearrangement and Homolytic Decomposition of meso- and DL-3,4-Di(1-cyclohexen-1-yl)-2,2,5,5-tetramethylhexanemeso- and DL-3,4-di(1-cyclohexen-1-yl)-2,2,5,5-tetramethylhexane (3a) were prepared by an improved reduction procedure (Li/C2H5NH2) from meso- and DL-2,2,5,5-tetramethyl-3,4-diphenylhexane. Products of two competing thermal transformations, C  -  C cleavage vs. Cope rearrangement, were isolated and identified. From a kinetic analysis of this system of reactions, characteristic activation enthalpies and entropies were obtained for the competing transformations. The standard heat of formation of meso-3a (ΔHf0(g) = -58.4 ± 1.2 kcal/mol) was determined by combustion calorimetry and by measurement of its heat of sublimation. A strain enthalpy Hs (meso- 3a) = 10.2 ± 1.2 kcal/mol was derived therefrom. Force-field calculations of the diastereomers of 3a and the Cope products 8a were performed by using MM2, MM2ERW, and MM3 in order to analyse the conformational situation. The calculated ΔHf0(g) values for meso-3a are higher than the experimental value by 4.4 (MM2), 5.2 (MM2ERW), and 14.5 (MM3) kcal/mol. Obviously, the three computational methods require reliable parameters for highly branched olefins like 3a and 5a. From the experimental heat of formation ΔHt0(g) and strain enthalpy Hs of meso-3a and its ΔH* of homolysis the stabilization energy of the allylic radical 4 was determined to be 12.6 ± 1.5 kcal/mol.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260119
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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Geminal Substituent Effects, 15.Part 14: Ref.[6]. Enthalpies of Formation of a Series of Fluorinated Hydrocarbons and Strain-Free Group Increments to Assess Polar and Anomeric Stabilization and StrainDedicated to Professor Dieter Seebach on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1333-1344 
    Details
    ISSN: 0947-3440
    Keywords: Benson increments ; Fluorohydrocarbons ; Anomeric stabilization ; Thermochemistry ; Fluorine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enthalpies of combustion, ΔHc0, and enthalpies of vapourization, ΔHvap0, for nineteen fluorohydrocarbons containing the groups CF, CF2, and CF3 were measured calorimetrically. From these data, enthalpies of formation, ΔHf(g), were calculated and were partitioned into new strain-free group increments of the Benson and v. Schleyer type: CH3[F] = -42.1; CH2[F, C] = -37.1; CH[F, 2 C] = -35.7; C[F, 3 C] = -39.6; CH2[2 F] = -61.0; CH[2 F, C] = -71.7; C[2 F, 2 C] = -67.3; CH[3 F] = -110.8; C[3 F, C] = -131.4; C[4 F] = -150.4; F[C] = -195.7 kJ mol-1. These increments now allow the calculation of the enthalpies of formation of a large family of homologous fluorohydrocarbons. Fluorine substitution, in general, stabilizes saturated hydrocarbon structures. A new concept, which was proposed recently for ethers, acetals, ketals, and orthoesters, for the analysis of the values of the increments for CH3, CH2, CH, and C groups with their different neighbouring atoms (given in brackets), is successfully applied to fluorohydrocarbons. In this method, the number of pairwise geminal interactions X—C—Y between all attached atoms X and Y is counted. The anomeric stabilization in geminal difluoromethylene groups taken from the F—C—F interaction is found to be 8 kJ mol-1 smaller than the O—C—O interaction for acetals and ketals, in agreement with calculations in the literature.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970709
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  • 8
    Electronic Resource
    Electronic Resource
    Does the Anomeric Effect in Ketals Depend on the Hybridization of the Central Carbon Atom? (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2323-2332 
    Details
    ISSN: 1434-193X
    Keywords: Acetals ; Small-ring ketals ; Strain ; Thermochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enthalpies of formation ΔHf°(g) of ketals prepared from cyclopropanone, cyclobutanone, cyclopentanone, cyclohexanone, and 7-norbornanone with methanol, ethylene glycol, and 2,2-dimethyl-1,3-propanediol, as well as of acetals/ketals of acyclic aldehydes and ketones, have been determined by measuring their heats of combustion and their heats of sublimation/vaporization. Group increments defining the strain-free energy level have been derived from the collected experimentally determined ΔHf°(g) values of unstrained acetals and ketals, and the anomeric stabilizations of these groups (given in brackets) have been calculated from a comparison of their group increments with those of ethers: CH2[2O, C] -64.9 (-20.2), CH[2O, C] -63.5 (-21.3), C[2O, 2C] -61.9 (-26.8), CH[2O, Ph] -58.4 (-16.2), C[2O, Ph, C] -56.3 (-21.2), C[2O, 2Ph] -67.1 (-32.0) kJ mol-1. Enthalpies of formation ΔHf°(g) of cyclic and spirobicyclic ketals have also been determined experimentally and compared with values obtained from molecular mechanics calculations (MM3). The close agreement of the results shows that the anomeric interactions, which are already integrated in the MM3 force field, are not dissimilar in the small-ring cyclic and spirobicyclic ketals investigated in this study. The hybridization of the anomeric carbon atom apparently has no influence on the size of the anomeric effect detectable. The strain enthalpies of the cyclic and spirobicyclic ketals have therefore been calculated from their ΔHf°(g) values using the group increment scheme. Analysis and interpretation of all geminal interactions known in acetals/ketals is possible by means of a recently developed additivity scheme, and a single value of -38.6 kJ mol-1 has been obtained for the structural increment representing the inherent geminal O-C-O interactions.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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