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  • 1
    ISSN: 1434-4475
    Keywords: 3-Deoxy-D-arabino-2-heptulosonic acid ; 3-Deoxy-D-arabino-2-heptulose (Kamusol) ; Indium mediated allylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Eine kurzer und ökonomischer Syntheseweg für 3-Desoxy-D-arabino-2-heptulosonsäure (4) und 3-Desoxy-D-arabino-2-heptulose (Kamusol,8) wurde entwickelt. Im Schlüsselschritt der Synthesesequenz wurde die indiumunterstützte Allylierung vonD-Erythrose in wäßrigen Reaktionsmedien angewendet. Das mittels dieser Methode auf sieben Kohlenstoffatome verlängerte Kohlenhydrat-Grundgerüst konnte einfach in die Titelverbindungen übergeführt werden.
    Notes: Summary A short and economical synthesis of 3-deoxy-D-arabino-2-heptulosonic acid (4) and 3-deoxy-D-arabino-2-heptulose (kamusol,8) has been developed. In the key step of the reaction sequence, the indium mediated allylation ofD-erythrose in an aqueous solvent system was utilized generating a seven carbon backbone which was further transformed into the title compounds.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-601X
    Keywords: 25.85.W
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The A dependence of nuclear fission induced by stopped antiprotons has been measured. An unambiguous identification of the binary fission decay mode was provided by a coordinate measurement of complementary fission fragments in coincidence using a large-acceptance fission detector based on low pressure multiwire proportional chambers. A deep fissility minimum was observed nearA=100, in agreement with the general behaviour predicted by the liquid-drop model. An unexpectedly low and high fission probability was found for the Ag and Cu nuclei, respectively.
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  • 3
    ISSN: 1434-4475
    Keywords: Carbohydrates ; Dendrimers ; Spacer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Ausgehend von den Allyl- und Pent-4-enyl-β-D-glucopyranosiden4–7 können dieD-Glucosederivate8–15 dargestellt werden, welche am anomeren Zentrum unterschiedlich lange Spacereinheiten mit verschiedenen Endgruppen besitzen. Bei Reaktion von vier Äquivalenten des Caesiumsalzes von Propan-4-carboxy-1-yl-2,3,4,6-tetra-O-acetyl-β-D-glucopyranosid15 mit Pentaerythrityltetrabromid entsteht das tetravalente Molekül16.
    Notes: Summary Starting with allyl- and pent-4-enyl-β-D-glucopyranosides4–7, differentD-Glucose units (8–15) containing alkyl spacers of variable lenght and with different end groups can be prepared. Reaction of four equivalents of the caesium salt derived from propan-4-carboxy-1-yl-2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside15 with pentaerythrityltetrabromide yields the tetravalent molecule16.
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  • 4
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We found that hydrogen ion formation due to multielectron dissociative ionization by an intense-laser field is much less efficient with 1,3-cyclohexadiene than with its isomer 1,3Z,5-hexatriene (Z-HT). Moreover by suppressing the ionization barrier an intense-laser field ejects electrons most efficiently from molecular states of low ionization potential. After pumping 1,3-cyclohexadiene at 267 nm to its 1B2 state we probe the system by intense-laser field ionization with delayed 800 nm pulses. Monitoring of the parent ion C6H8+, of the main fragment C6H7+ and of H+ allows us to follow the motion from the 1B2 surface to the dark 2A1 state and from there towards the 2A1/1A1 conical intersection to the ground-state surface of the product. The measured 1B2 and 2A1 lifetimes are 43±3 and 77±7 fs, respectively, and the primary photoproduct cZc-HT is produced within 200 fs. © 1997 American Institute of Physics.
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  • 5
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: As in longer polyenes, the strong 1A1→1B2 band in the UV spectrum of 1,3Z,5-hexatriene (Z-hexatriene) has a weak precursor, the 1A1→2A1 transition. It was measured in this work by a conventional spectrometer. Whereas the wave number of the 0–0 transition is by 5400 cm−1 lower than that of the 1B2 origin, the vibrational contour indicates that the vertical transitions of thetwo bands nearly coincide. From the fast decay of the rotational anisotropy in the time-resolved measurements we conclude that this band is perpendicularly polarized. We measured the lifetime of the 2A1 state after pumping it directly by 250 fs pulses and probing the excited molecules by ionizing it by delayed pulses. The lifetimes decreased from several ps to 730 fs, when the excess energy was increased from near 0 to 4000 cm−1 and more. From the temperature dependence we infer a barrier of about 170 cm−1 (2 kJ/mol). © 1997 American Institute of Physics.
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