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  • Chemistry  (29)
  • Biochemistry and Biotechnology
  • Wiley-Blackwell  (29)
  • 1980-1984  (29)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 2563-2569 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,3-Alkadienoates as Dienophiles, Application in the Synthesis of (+)-(R)-LasiodiplodinMethyl 2, 3-alkadienoates 2 are shown to react at 80° with l, 1-dimethoxy-3trimethylsilyloxy-l, 3-butadiene (1) to give the adducts 3 in good yields. Rearrangement of 3, catalyzed by p-toluenesulfonic acid or by sodium methoxide, affords the 6-substituted methyl 4-hydroxy-2-methoxybenzoates 4 (R = H, CH3, C6H5). An analogous reaction sequence starting with (-)-(11 R)-dodeca-2, 3-dien-11-olide ((-)-6) and 1 leads, via the adduct (R)-7, to (+)-(R)-lasiodiplodin ((+)-8) with properties identical to those of the natural product. The allene lactone (-)-6 was prepared by an intramolecular Wittig condensation of (R)-5, produced from (-)-(R)-9-hydroxydecanoic acid.
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 115 (1982), S. 2487-2493 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Trinuclear Ruthenium Cluster Anions Containing Triorganylsilyl, -germyl, and -stannyl LigandsThe reaction of Na[HRu3(CO)11] with triorganylsilanes, -germanes, and -stannanes R'R2XH (X = Si, Ge, Sn; R, R' = organyl) affords trinuclear cluster anions of the type [HRu3(CO)10(XR2R')2]-, which can be isolated as the bis(triphenylphosphoranyliden)ammonium or the tetraethylammonium salts. The structure of an isosceles Ru3 triangle with one hydride bridge and two XR2R' ligands at the bridgehead ruthenium atoms is proposed for the anions on the basis of NMR evidence. The reaction proceeds under elimination of H2 and CO and is reversible; the formation of [HRu3(CO)10(SiEt3)2]- from [DRu3(CO)11]- and Et3SiH reveals the eliminated hydrogen to be arising from the cluster.
    Notes: Die Umsetzung von Na[HRu3(CO)11] mit Triorganylsilanen, -germanen und -stannanen R'R2XH (X = Si, Ge, Sn; R, R' = organyl) führt zu dreikernigen Clusteranionen des Typs [HRu3(CO)10(XR2R')2]-, die sich als Bis(triphenylphosphoranyliden)ammonium- bzw. Tetraethylammonium-Salze isolieren lassen. Aufgrund der spektroskopischen Befunde wird für die Anionen die Struktur eines gleichschenkligen Ru3-Dreiecks mit einer Hydridbrücke und zwei XR2R'-Liganden an den beiden Brückenkopf-Rutheniumatomen vorgeschlagen. Die Reaktion verläuft unter Eliminierung von H2 und CO und ist reversibel; die Bildung von [HRu3(CO)10(SiEt3)2]- aus [DRu3(CO)11]- und Et3SiH zeigt, daß der freigesetzte Wasserstoff aus dem Cluster eliminiert wird.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 3406-3412 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Trinuclear Ruthenium Cluster Anions of the Type [Ru3(CO)9(SiR21R2)(PR33)2]-The reaction of Na[HRu3(CO)10(SiR21R2)2] with phosphorous ligands leads to trinuclear cluster anions of the type [Ru3(CO)9(SiR21R2)(PR33)2]- which can be isolated as the bis(triphenylphosphoranyliden)ammonium salts. On the basis of the spectroscopic data the structure of an isosceles triangle is proposed for the anions; the two phosphane ligands and the silyl group are assumed to occupy an equatorial position at each of the three ruthenium atoms.
    Notes: Die Umsetzung von Na[HRu3(CO)10(SiR21R2)2] mit phosphorhaltigen Liganden PR33 führt zu dreikernigen Clusteranionen des Typs [Ru3(CO)9(SiR21R2)(PR33)2]- die sich als Bis(triphenyl-phosphoranyliden)ammoniumsalze isolieren lassen. Aufgrund der spektroskopischen Befunde wird für die Anionen die Struktur einem gleichschenkligen Dreiecks vorgeschlagen; die beiden Phosphanliganden und die Silylgruppe besetzen dabei offenbar je eine äquatoriale Position an eines der drei Rutheniumatome.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 182 (1981), S. 2095-2103 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The heats of copolymerization of styrene and methyl methacrylate were measured by means of differential thermal analysis (DTA). Extrapolating the DTA curves to time zero, monomer reactivities and the ratio of the rate constants of termination can be obtained by a new method of evaluation. Calibration is not necessary for this procedure. With calibration, however, the rates and the heats of polymerization can also be measured. The data agree well with those reported in the literature.
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  • 5
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: This paper deals with the kinetics of the polymerization of ethylene catalysed by the soluble Ziegler-catalyst Cp2TiPropylCl/AlEtCl2. By means of a special method it was possible to study the kinetics of the initial instationary homogeneous part of the polymerization. The dependences of the initial rates on the catalyst components prove that the polymerization active species is formed in two successive very dynamic equilibria. The primary complex equilibrium is entirely located on the right hand side, whereas the second equilibrium depends considerably on the ratio of the catalyst components and is shifted on the active species side only at very high Al/Ti ratios. Because of this location of the two successive equilibria the dependence of the polymerization velocity vp on the charged Al concentration (that is, the Al isotherm) has to show a sigmoidal curve course in the inital part, which experimentally is confirmed exactly. Finally, this extensive kinetical analysis leads to the complete reaction scheme of the polyreaction and by mathematical modelling to the quantitative calculation and description of the experimental curves and dependences (e.g., Al-isotherm).
    Additional Material: 10 Ill.
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  • 6
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The monomer reactivity ratios and the ratio of the rate constants of termination in the 2-hydroxyethyl methacrylate/methyl methacrylate system were measured by differential thermal analysis. The data for the monomer reactivity ratios agree well with data calculated from the Q-e scheme.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 647-656 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXII. 1H-N.M.R. and U.V. Spectroscopic Investigations on the Isomerization of Pseudobases of Unsymmetrically Substituted 2, 4, 6-Triarylpyrylium SaltsThe kinetics and mechanism of the isomerization of the title compounds, the pentene 1,5-diones 2 and 3, were studied by 1H-n.m.r. and u.v. spectroscopy. The equilibrium constants measured vary little near 1, indicating the small influence of substituents on the equilibrium position. The mutual rearrangement 2⇄3 proved to be a base-catalized reaction which is characterized by strictly linear Hammett correlation between 1g k and Σσp. The results obtained suggest resonance-stabilized anions of type4 as intermediates. - Pseudobases of 3-alkyl-2, 4, 6-triarylsubstituted pyrylium salts do not undergo a reversible isomerization.
    Additional Material: 2 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 105 (1982), S. 31-38 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: In soluble Zieger-catalyst systems of the type Cp2TiRCl/AlEtCl2/ethylene the polymerization active species is formed in two successive equilibria. This reaction sequence involves an intermittend process of the chain propagation and subsequently a particular molecular weight distribution, which results in a new determination of the chain propagation constant by means of the distribution development. The congruence of experimental distributions with theoretical distributions calculated on the basis of the reaction scheme of the two successive equilibria leads by means of the highest formed polymerization degree, which is only accessable by the calculated distributions, to the determination of the chain propagation constant from each experimental distribution. Hence, all by means of the measured dependences of the distribution development on the reaction time and on the concentration of active species determined chain propagation constants result in the same value of 120 l/mol. s for the insertion in a Ti-ethyl-bond for instance and prove so the accuracy of this method.
    Notes: Bei löslichen Ziegler-Katalysator-Systemen vom Typ Cp2 TiRCl/AlEtCl2/Ethylen wird die polymerisationsaktive Spezies in zwei aufeinanderfolgenden Gleichgewichtsreaktionen gebildet. Diese Reaktionsfolge bedingt ein intermittierendes Kettenwachstum und damit eine besondere Molmassenverteilung, die ihrerseits über den Weg der Verteilungsentwicklung zu einer neuen Bestimmungsmethode der Wachstumskonstanten führt. Nach Kongruenz von experimentellen Verteilungen mit aufgrund des Reaktionsschemas der successiven Gleichgewichte berechneten Verteilungen ermöglicht der nur über die berechneten Verteilungen zugängliche höchste entstandene Polymerisationsgrad die Ermittlung der Kettenwachstumskonstanten aus jeder experimentellen Verteilung. Die so z.B. aus den gemessenen Abhängigkeiten der Verteilungsentwicklung von Reaktionszeit und Konzentration an aktiver Spezies bestimmten Werte der Kettenwachstumskonstante führen stets zum gleichen Wert von z. B. 120 l/mol·s für die Insertion in eine Ti-Ethyl-Bindung und belegen so die Richtigkeit dieses Zugangs zu kw bei intermittierendem Wachstum.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 94 (1981), S. 25-47 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Elementary processes of soluble Ziegler-catalysts of the type (C5H5)2TiRCl/AlEtnClm have been investigated by means of 13C-NMR-spectroscopy. Using 13C enriched ethylene in the NMR-experiment we succeeded in looking directly for the first time into the reacting and polymerizing system. According to this insight, for instance, there is no precoordination of the monomer on the primary complexes and the insertion occurs unambiguously in the Ti—C-bond. Furthermore the transfer of the chains between two Ti-centres leads to interesting spectroscopical detail.
    Notes: Elementarprozesse löslicher Ziegler-Katalysatoren vom Typ Cp2TiRCl/AlEtnClm wurden mit Hilfe der 13C-NMR-Spektroskopie studiert, die sich dabei durch Einsatz von mit 13C angereichertem Ethylen als eine Möglichkeit erwiesen hat, direkten detaillierten Einblick in das reagierende und polymerisierende System zu gewinnen. Danach ist durch die Komplexbildung die Elektronendichte am Titan erniedrigt. Es erfolgt keine spektroskopisch nachweisbare Vorkoordination des Monomeren. Das System Cp2TiEtCl/AlEtCl2 ist bereits bei 200 K polymerisationsaktiv. Die Insertion erfolgt eindeutig in der Titan-Kohlenstoffbindung. Das System Cp2TiEtCl/AlEt3 ist - auch wenn noch keine Reduktion stattgefunden hat - nicht polymerisationsaktiv.
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  • 10
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The primary and most rapid reaction in the soluble Ziegler catalyst system Cp2TiEtCl/AlEtCl2 is the formation of the primary complex equilibrium. By means of 13C-NMR spectroscopy and quantitative line shape analysis the kinetic and thermodynamic data of this equilibrium have been discovered for the first time. So for instance the primary complex formation is a diffusion controlled reaction with a second order rate constant in the order of magnitude 1010 to 1011. The equilibrium constant of the primary complex was determined as to be 5 · 103 ≤ K1 ≤ 5 · 104 l/mol at 240 K. By this way the Al isotherm, for the first time measurable, proved the exact Al:Ti = 1:1 stoichiometry of the primary complex.
    Notes: In dem löslichen Ziegler-Katalysator-System Cp2TiEtCl/AlEtCl2 stellt sich zwischen den Komponenten in erster und schnellster Reaktion das Primärkomplexgleichgewicht ein. Die kinetischen und thermodynamischen Daten dieses Primärkomplexgleichgewichts konnten durch dynamische 13C-NMR-spektroskopische Untersuchungen mit quantitativer Linienformanalyse erstmalig eruiert werden. So erfolgt z. B. die Primärkomplexbildung in einer diffusionskontrollierten Reaktion, deren Geschwindigkeitskonstante (bei 280 K) zu k = 1010 bis 1011 (1/mol · s) eingegrenzt werden konnte. Die Gleichgewichtskonstante des Primärkomplexes ergab sich zu K1 = 5 · 103 bis 5 · 104 (1/mol) bei 240 K. Die Al-Isotherme bewies hier ferner die exakte Al : Ti = 1:1 Stöchiometrie. Es lieght nahe, daß der Primärkomplex ein Donor-Akzeptoraddukt ist, in dem ein freies Elektronenpaar des Titanchloroliganden gegenüber dem Al-Alkyl-Monomeren als Lewis-Base fungiert.
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