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  • 1
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung Aus den Blättern vonAlstonia scholaris R. Br. sind Pikrinine (Ia), Akuammidine und ein neues, bisher in Pflanzen nicht gefundenes Alkaloid, Pikralinal (Ib) isoliert worden. Pikralinal ist eine SchlÜsselsubstanz fÜr die Biosynthese vieler Alkaloide des Pikralimatypus.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wurde die mit γ,γ′-Azo-γ-cyan-n-valeriansäure initiierte Polymerisation von Styrol bei 100°C in Dimethylformamid untersucht. Die Polymerisationsgeschwindigkeit ist proportional der Wurzel der Initiatorkonzentration und der Potenz 3/2 der Monomerenkonzentration. Die Übertragungskonstante für das Styrolradikal und Dimethylformamid betrug bei 100°C Cs = 1,08 · 10-4.In Gegenwart des genannten Azo-Initiators wurden unter verschiedenen Bedingungen niedrigmolekulare Polystyrole hergestellt. Ihr Molekulargewicht war osmotisch nicht mehr meßbar und wurde an fraktionierten und unfraktionierten Proben durch Viskositätsmessungen und Endgruppentitrationen ermittelt. Die Ergebnisse werden mit denen anderer Autoren verglichen.
    Notes: The polymerization of styrene using γ,γ′-azo (γ-cyano-n-valeric acid) as initiator was studied at 100°C. in DMF solution.It has been shown that the rate of polymerization is proportional to the square root of the initiator concentration and 3/2 power of the monomer concentration. The chain-transfer constant for styrene radicals and dimethylformamide has been determined at 100°C., with the result Cs = 1.08 · 10-4.Several samples of polystyrene of low molecular weights (below the osmotic pressure range) were prepared under a variety of conditions in the presence of this initiator. Their molecular weights were determined by viscosity and end group titrations, both for fractionated and unfractionated samples. The results are compared with those obtained by other workers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modes of thermal and photochemical cycloaddition of even linear polyenes are examined using the simple concept of activation hardness. The results are in agreement with the well-known Woodward-Hoffman rules. [R.B. Woodward and R. Hoffmann, The Conservation of Orbital Symmetry (Academic Press, New York, 1989)]. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The FSGO model has been used to make ab initio calculations of the geometry of B2H5+ ion. The results indicate that the acetylenic structure has the lowest energy (-43.881 a.u.) and the planar structure has the highest energy (-43.838 a.u.). The energy of the non-symmetric structure is only slightly higher (-43.879 a.u.) than that of the acetylenic one. Results of CNDO/2 calculations reported here also predict the acetylenic structure to be the most stable one.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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