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  • 1975-1979  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 7 (1977), S. 161-171 
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal and molecular structure of 2,7-anhydro-l-glycero-β-d-manno-octulopyranose has been determined by X-ray analysis. Crystal data area = 9.590(4),b = 7.404(5),c=7.363(4) Å, β = 101.79(3)°,Z = 2, space groupP21. The phase problem was solved by direct methods, using diffractometer data, and the structure was refined by least-squares techniques to a finalR value of 3.7%. The anhydro ring system is built up by the pyranosyl chair in the1 C 4 conformation, the five-membered ring in theE 0 conformation, and a boat-shaped seven-membered ring. Potential energy calculations show that the positions of the terminal CH2OH groups are determined by hydrogen bonds.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 7 (1977), S. 147-155 
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An x-ray analysis of two natural compounds isolated fromPiper sanctum confirmed thetrans configuration for 5-(8-methoxy)cinnamyliden-4-methoxy-but-3-enolide [piperolide (I)] and for 5-[trans-(z)-β,γ-epoxy-α-methoxycinnamyliden]-4-methoxy-2(5H)-furanon [epoxypiperolide (II)]. The space groups arePbca [a = 44.174(3),b = 8.056(3),c = 7.515(4) Å] for (I) andP21/c [a = 11.351(4),b = 8.292(5),c = 14.292(2) Å, β = 96.28(2) °] for (II). The structures were solved by direct methods and refined by least-squares techniques toR = 4.8% (I) andR = 7.5% (II). The stereochemistry of the semicyclic double bond is in favor of theZ-isomers.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Redetermination of the Crystal and Molecular Structure of Heptasulfur Imide, S7NHThe following data were obtained from a single crystal x-ray structure analysis of S7NH carried out at -160°C and leading to a R value of 0.026: space group Pbnm, lattice dimensions a = 7.607, b = 7,823, c = 13.091 Å, Z = 4, density 2.04 g · cm-3. The molecules consist of puckered rings of site symmetry Cs with average bond distances dSS = 2.053, dSN = 1,676, dNH = 0,91 Å. The coordination of the nitrogen is almost planar which ist rationalized in terms of a 3-center, π-bond. There are indications for weak intermolecular S…H hydrogen bonds.
    Notes: Eine bei -160°C ausgeführte und bis zum R-Wert von 2,6% verfeinerte Röntgenstrukturanalyse von Heptaschwefelimid ergab folgende Kristalldaten: Raumgruppe Pbnm, Gitterkonstanten a = 7,607, b = 7,823, c = 13,091 Å, Z = 4, Dichte 2,04 g · cm-3. Die kronenförmigen S7NH-Moleküle besitzen die Lagesymmetrie Cs; die mittleren Kernabstände sind dSS = 2,053, dSN = 1,676, dNH = 0,91 Å. Das Stickstoffatom ist nahezu planar koordiniert, was mit einer Dreizentren-π-Bindung erklärt wird. Die Struktur enthält keine N…H-, wohl aber schwache intermolekulare S…H-Wasserstoffbrücken.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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