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  • 1985-1989  (3)
  • 1980-1984  (3)
  • 1970-1974  (1)
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  • 1
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 84 (1980), S. 198-202 
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Rheologica acta 9 (1970), S. 525-534 
    ISSN: 1435-1528
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung In diesem Beitrag wird auf einige Aspekte rheologischer Modelle, die partielle Differentialquotienten enthalten, eingegangen. Nach einem kurzen historischen Überblick über die Anwendungen dieser Differentialquotienten in der Rheologie wird eine mathematische Formulierung gegeben. Auch wird gezeigt, wie diese Differentialquotienten in rheologische Modelle eingeführt werden können; das dynamische Verhalten eines einfachen Modells wird mit Hilfe verschiedener Experimente, wie sie oft an viskoelastischen Stoffen durchgeführt werden, berechnet. Das Modell wird anhand der Ergebnisse einiger Messungen an Nylon 6- und PETP-Fasern geprüft; dies veranlaßte die Einführung eines elastischen Terms. Schließlich wird die Beziehung zwischen partielle Differentialquotienten enthaltenden Modellen und den wichtigsten Gleichungen der Theorie der linearen Viskoelastizität in großen Zügen angegeben.
    Notizen: Summary In this contribution some aspects of rheological models containing fractional derivatives are shown. After a short historical review of the application of fractional derivatives in rheology, a mathematical formulation of these derivatives is given. The possibility of using fractional derivatives in the construction of rheological models is demonstrated. The behaviour of a simple fractional derivative model is calculated in a number of experiments, often performed on fibres. The model is checked against the results of some measurements on nylon 6 and PETP fibres, which leads to the addition of an elastic term. Finally, in broad outline, the relation between fractional derivative models and the principal expressions of the theory of linear viscoelasticity is indicated.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    ISSN: 1573-9171
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Conclusions A short general scheme was developed for the synthesis of a series of bi- and tricyclic compounds containing a 3-oxa-bicyclo[3.3.0]octane fragment on the basis of the successive acylallyloxylation of the double bond in the hexacarbonyldicobalt complexes of conjugated enynes and subsequent intramolecular [2+2+1]-cycloaddition.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    ISSN: 1573-9171
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Conclusions 1. Reactions of dicoboalt hexacarbonyl complexes of conjugated enynes with cationoid reagents of the type acyl-, alkyl-, nitronium, and arylsulfene-tetrafluoroborates leads to formation of cationoid intermediates which are stable in solution. These cationoid intermediates may then react with nucleophiles of the water or methanol type with formation of covalent adducts. 2. The observed two-step AdE-reaction is a suitable route for synthetic use of enynes, which is shown for the case of the syntheses of a number of monoterpenoids.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    ISSN: 1573-9171
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Conclusions 1. From MNDO quantum chemical calculations, opening of the episulfonium ion ring by neutral nucleophiles X (X=NH3 and HCN) and related SN2 reactions of protonated methylthiol (PMT) with X proceed through formation of pre-reaction complexes in which X is coordinated either at the reacting C atom or (only in opening of episulfonium ion rings) at the center of the C-C bond. 2. In their electronic structure, the transition states for the reactions are reminiscent of a carbocation simultaneously reacting with the attacking and the leaving nucleophilic fragments (X ⋯ $$\mathop C\limits^ + $$ ⋯S). 3. Opening of episulfonium ion rings proceeds slightly more easily (Ea ∿ 10–12 kcal/mole) than substitution in PMT (Ea ∿ 22–25 kcal/mole). The ease of ring opening for episulfonium ions is due to the large exothermicity of the reaction and the lower internal activation barrier compared with SN2 reactions in PMT.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    ISSN: 1573-9171
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Conclusions 1. According to MNDO quantum chemical calculations, the reaction of the episulfonium ion with neutral nucleophiles X (X=NH3 and HCN) is facilitated in the presence of a methyl group at the C* atom under attack (opening in accordance with Markovnikov's rule) and is hindered in the presence of a methyl group on the adjacent C atom (opening contrary to Markovnikov's rule). Conversely, SN2 substitution of protonated alkylthiols by the same nucleophiles X is retarded upon introduction of a methyl group at the reacting atom C*. 2. Opening of the C-substituted episulfonium ion in both directions can go through the same pre-reaction complex in which the nucleophile is coordinated approximately at the center of the basal C-C bond. Opening contrary to Markovnikov's rule also can go through an alter-native pre-reaction complex in which the nucleophile is coordinated at the unsubstituted C atom. 3. Analysis of Ea and the enthalpy of reaction δH using the Marcus equation allows us to explain the apparent anomaly in the behavior of Ea upon substitution of episulfonium ions.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 16 (1984), S. 1481-1494 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Rates and thermodynamic data have been obtained for the reversible self-termination reaction: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm R}^ \cdot + {\rm R}^ \cdot \mathop{\buildrel\longleftarrow\over\longrightarrow}^{2k1}_{2k_{-1}}D $$\end{document} Involving aromatic 2-(4′dimethylaminophenyl)indandione-1,3-yl (I), 2-(4′diphenylaminophenyl)indandione-1,3-yl (II), and 2,6 di-tert-butyl-4-(β-phthalylvinyl)-phenoxyl (III) radicals in different solvents. The type of solvent does not tangibly affect the 2k1 of Radical(I), obviously due to a compensation effect. The log(2k1) versus solvent parameter ET(30) curves for the recombination of radicals (II) and (III) have been found to be V shaped, the minimum corresponding to chloroform. The intensive solvation of Radical (II) by chloroform converts the initially diffusion-controlled recombination of the radical into an activated reaction. The log (2k-1) of the dimer of Radical (I) has been found to be a linear function of the Kirkwood parameter (ε - 1)/(2ε + 1), the dissociation rate increasing with the dielectic constant of the solvent. The investigation revealed an isokinetic relationship for the decay of the dimer of Radical (I), an isokinetic temperature β = 408 K and isoequilibrium relationship for the reversible recombination of Radical (I) with β° = 651 K. For Radical (I) dimer decay In(2k-1) = const + 0.8 In K, where K is the equilibrium constant of this reversible reaction. The transition state of Radical (I) dimer dissociation reaction looks more like a pair of radicals than the initial dimer. The role of specific solvation in radical self-termination reactions is discussed.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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