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  • 1
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis, Structure, and Cope Rearrangement of Some 3,7-Dicyano-1,5-dimethylsemibullvalenesAddition of trimethylsilyl cyanide to the bicyclo[3.3.0]octane-3,7-dione 8 followed by the reaction of the diastereomeric O-silylated biscyanohydrins 12 with phosphoryl chloride in boiling pyridine yields a 2:1 mixture of the regioisomeric unsaturated dinitriles C2-13 and Cs-13. These are converted by an excess of N-bromosuccinimide to the tribromo- (14a) and the isomeric tetrabromodinitriles 14b and 15a which are separated by crystallization and by selective reaction of 15a with diethyl phosphite/triethylamine. The structure of the predominant, unsymmetrical tetrabromodinitrile 15a is determined by an X-ray diffraction analysis. Zinc/copper reagent in boiling ether smoothly debrominates the tetrabromodinitriles 14b and 15a affording the 2,6- (2b) and 2,4-dibromo-3,7-dicyanosemibullvalene 2a, respectively. However, extended heating of 15a in tetrahydrofuran in the presence of zinc/copper reagent produces the bromo-3,7-dicyanoscmibullvalene 1c⇌1c′ Bromine/lithium exchange of the latter by tert-butyllithium at -100°C and quenching of the lithio-3,7-dicyanoscmibullvalene 1d with methanol, methan-[D]ol, and cyanogen yield the semibullvalenes 1a, 1b⇌1b′, and 1e⇌1e′, respectively. The rates of the degenerate Cope rearrangement of the dibromo-3,7-dicyanosemibullvalenes 2a and b are calculated from the exchange broadening of carbon-13 NMR signals in the temperature range 200-290 K. For 200 K one obtains k = 260 s-1, ΔG≠ = 39.1⇌1.5 kJ·mol-1 (2a) and k = 1160 s-1, ΔG≠ = 36.6±0.6 kJ·mol-1 (2b). Thus, the strong deceleration of the degenerate Cope rearrangement relative to that of the 3,7-dicyanosemibullvalene 1a (k = 1.53·106 s-1, ΔG≠ = 24.6±0.3 kJ·mol-1 at 200 K) depends only little on the position of the bromine atoms. For the valence tautomeric equilibria of the 3,7-dicyanosemibullvalenes 1b⇌1b′ (K = 1.112±0.001 at 298 K), 1c⇌1c′ (0.065±0.02 at 300 K), 1e⇌1e′ (0.29±0.02 at 300 K), and the known bromosemibullvalenes 18b⇌18b′ (0.2±0.02 at 300 K) the constants K are determined using relative temperature gradients of carbon-13 shifts or Saunders' isotopic pertubation method. The atomic distances as revealed by X-ray diffraction analyses of the bromo-3,7-dicyanosemibullvalenes 1c and 2a demonstrate that both do not undergo a Cope rearrangement in the crystal. On the contrary, a statistical orientational disorder in the crystal is observed for 2b which is indicative of a degenerate Cope rearrangement in the solid state.
    Notes: Addition von Trimethylsilylcyanid an das Bicyclo[3.3.0]octan-3,7-dion 8 und nachfolgende Umsetzung der diastereomeren O-silylierten Biscyanhydrine 12 mit Trichlorphosphanoxid in siedendem Pyridin ergibt ein 2:1-Gemisch der regiosiomeren ungesättigten Dinitrile C2-13 und Cs-13. Diese werden mit überschüssigem N-Bromsuccinimid in die Tribrom- (14a) und isomeren Tetrabromdinitrile 14b und 15a übergeführt, die durch Kristallisation und selektive Reaktion von 15a mit Diethylphosphit/Triethylamin getrennt werden. Die Struktur des überwiegenden, unsymmetrischen Tetrabromdinitrils 15a wird durch eine Röntgenstrukturbestimmung aufgeklärt. Zink/Kupfer in siedendem Ether debromiert die Tetrabromdinitrile 14b und 15a glatt zu dem 2,6- (2b) bzw. 2,4-Dibrom-3,7-dicyansemibullvalen 2a. Längeres Erhitzen von 15a mit Zink/Kupfer in Tetrahydrofuran führt dagegen zum Brom-3,7-dicyansemibullvalen 1c⇌1c′. Brom/Lithium-Austausch an 1c⇌1c′ mit tert-Butyllithium bei -100°C und Umsetzung des Lithio-3,7-dicyansemibullvalens 1d mit Methanol, Methan-[D]ol und Dicyan ergeben die Semibullvalene 1a, 1b⇌1b′ bzw. 1e⇌1e′. Die Geschwindigkeit der entarteten Cope-Umlagerung der Dibrom-3,7-dicyansemibullvalene 2a und b wird aus der Austauschverbreiterung von 13C-NMR-Signalen im Bereich von 200-290 K bestimmt. Bei 200 K gilt für 2a k = 260 s-1, ΔG≠ = 39.1±1.5 kJ·mol-1, für 2b k = 1160 s-1, ΔG≠ = 36.6±0.6 kJ·mol-1. Die starke Verzögerung der entarteten Cope-Umlagerung im Vergleich zu der des 3,7-Dicyansemibullvalens 1a (k = 1.53·106 s-1, ΔG≠ = 24.6±0.3 kJ·mol-1 bei 200 K) hängt somit nur wenig von der Stellung der Bromatome ab. Die Konstanten K der Valenztautomerie-Gleichgewichte der 3,7-Dicyansemibullvalene 1b⇌1b′ (K = 1.112±0.001 bei 298 K), 1c⇌1c′ (0.065±0.02 bei 300 K), 1e⇌1e′ (0.29±0.02 bei 300 K) und der bekannten Bromsemibullvalene 18⇌18′ (0.2±0.02 bei 300 K) werden aus relativen Temperaturgradienten 13C-chemischer Verschiebungen bzw. mit Hilfe von Saunders' Isotopenstörungs-Methode erhalten. Die durch Röntgenstrukturbestimmung ermittelten Atomabstände der Brom-3,7-dicyansemibullvalene 1c und 2a zeigen, daß bei beiden im Kristall keine Cope-Umlagerung stattfindet. Dagegen beobachtet man eine statistische Orientierungsfehlordnung im Kristall des 2,6-Dibrom-3,7-dicyansemibullvalens 2b, die auf eine entartete Cope-Umlagerung im festen Zustand hinweist.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 1801-1806 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: 3,7-Dicyano-2,6-dimethoxy-1,5-dimethylsemibullvaleneMichael reaction of dimethyl methylmalonate and acrylonitrile affords a 92% yield of the diesternitrile 4a, which is quantitatively hydrolysed to give the monoacid 4b. When subjected to Kolbe electrolysis, 4b produced a 1:1 mixture (21% yield) of the diastereomeric bis(esternitriles) meso- and rac-5. In the Dieckmann condensation of this mixture with potassium tert-butoxide, meso-5 furnishes 54% of the monocyclic α-cyanoketone 6a while rac-5 affords 68% of the bicyclic bis(β-cyanoenol) 7c. The products of the condensation exist predominantly in these tautomeric forms (6a and 7c, respectively) and are separated on the basis of their different acidity. Diazomethane methylates 7c to provide the bis(β-cyanoenolether) 10 (79% yield), which is brominated by N-bromosuccinimide to yield the bis(bromo-β-cyanoenolether) 11 (51% yield). Zinc/copper reagent debrominates 11 to afford the title compound 1d (49% yield). The rate constants of the degenerate Cope rearrangement of 1d in the temperature range of 209-293 K are calculated from the exchange broadening of the signals of 4-H, 8-H and the methoxy protons. The rate constant at 200 K is k = 57 s-1 and the free enthalpy of activation ΔG≠ = 41.6 ± 0.4 kJmol-1. Thus, the methoxy groups decelerate the Cope rearrangement by a factor of 3 · 104 corresponding to an increase of the activation barrier by 17 kJmol-1 relative to that of the 3,7-dicyanosemibullvalene 1a.
    Notes: Michael-Addition von Methylmalonsäure-dimethylester an Acrylnitril führt mit 92% Ausbeute zum Diesternitril 4a, das quantitativ zur Monosäure 4b hydrolysiert wird. Deren Kolbe-Elektrolyse ergibt mit 21% Ausbeute ein (1:1)-Gemisch der Diastereomeren Bis(esternitrile) meso- und rac-5. Bei der Dieckmann-Kondensation dieses Gemischs mit Kalium-tert-butylat erhält man aus meso-5 mit 54% Ausbeute das monocyclische α-Cyanketon 6a, aus rac-5 mit 68% Ausbeute das bicyclische Bis(β-cyanenol) 7c. Die Kondensationsprodukte liegen hauptsächlich in diesen tautomeren Formen (6a bzw. 7c) vor und werden aufgrund ihrer unterschiedlichen Acidität getrennt. Diazomethan methyliert 7c zum Bis(β-cyanenolether) 10, der durch N-Bromsuccinimid zum Bis(brom-β-cyanenolether) 11 bromiert wird. Mit Zink/Kupfer entsteht daraus die Titelverbindung 1d. Die Geschwindigkeitskonstanten der entarteten Cope-Umlagerung von 1d werden im Bereich 209-293 K aus der Austauschverbreiterung der Signale von 4-H, 8-H und der Methoxyprotonen errechnet. Bei 200 K ist die Geschwindigkeitskonstante k = 57 s-1 und die Freie Aktivierungsenthalpie ΔG≠ = 41.6 ± 0.4 kJmol-1. Die Methoxygruppen verzögern somit die Cope-Umlagerung um den Faktor 3 · 104, was einer Erhöhung der Aktivierungsbarriere (relativ zu der des 3,7-Dicyansemibullvalens 1a) um 17 kJmol-1 entspricht.
    Additional Material: 6 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 44-54 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Poly[1-(trimethylsilyl)propyne] (PTMSP) is an unusual polyyne material which is optically clear, exhibits high solubility in nonpolar organic solvents, and good oxygen compatibility. By contrast, polyacetylene is black, insoluble, and is unstable in oxygen. The long term stability of PTMSP has been determined by a combination of thermal gravimetric analysis (TGA) and permeability test procedures under a number of different isothermal aging conditions. The use of commercial antioxidants at up to 2 weight percent improves the long term stability of PTMSP. The presence of the antioxidant has no effect on the surface fluorination of PTMSP. Testing of PTMSP films for over eight months shows no change in either permeability or selectivity in contrast to previously reported data.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 25 (1987), S. 311-323 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Blends of various poly(aryl ether ketones) have been found to exhibit a range of miscibility and isomorphic behavior. This range is dependent on molecular weight; however, for poly(aryl ether ketones) with number-average molecular weight of 20,000, this range is about ±25% difference in ketone content. All miscible blends exhibit isomorphism, and all immiscible blends exhibit no evidence of isomorphism. The dependence of the glass transition temperature Tg versus composition exhibits a minimum deviation from linearity whereas the melting temperature Tm versus composition exhibits a pronounced maximum deviation from linear behavior.The crystalline melting point versus composition for isomorphic blends is considerably different than for random copolymers with isomorphic units. Homopolymers and random copolymers exhibit a melting point that is a linear function of ketone content (increasing ketone content increases Tm). For blends, the melting point is essentially the same as that of the higher melting constituent until high levels of the lower melting constituent are present. The observed melting point versus composition behavior will be interpreted using classical theory to calculate the components of the liquid and crystalline phase compositions. As a miscible blend is cooled from the melt, essentially pure component of the highest melting point crystallizes out of solution, as predicted by calculated solid-liquid phase diagrams. This occurs until the crystallization is complete owing to spherulitic impingement. At high concentrations of the lower melting constituent, lower melting points will be observed because the highest melting constituent will be depleted before the crystallization is complete.In many miscible blends involving addition of an amorphous polymer to a crystalline polymer, the degree of crystallinity of the crystalline polymer has been shown to increase. On the basis of evidence presented here, it is hypothesized that dilution by a miscible, amorphous polymer allows for a higher level of crystallinity.
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electrophoresis 8 (1987), S. 25-28 
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Protein molecular weight standards labeled with different fluorochromes were tested for their usefulness in following the protein transfer from sodium dodecyl sulfate-polyacrylamide gels to nitrocellulose and for electro-elution of proteins from polyacrylamide gels. Dichlorotriazynylaminofluorescein labeled proteins appear to be useful for both purposes as they are stable, their detection sensitivity was high (about 10 ng of protein on nitrocellulose) and the coupling of the fluorochrome did not appreciably change the molecular weight of any protein examined. On the other hand, proteins labeled with tetramethylrhodamine isothiocyanate, or its heterocyclic derivative, were of limited usefulness as standards. Labeled proteins of molecular weight below 20 kDa formed diffuse bands on gels. Therefore, these particular fluorescent protein standards appear to be useful in following the elution from gels, or as references on nitrocellulose, only for proteins larger than 20-25 kDa.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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