Alkyloxycarbonyl group migration in furanosides

A migration of methyloxycarbonyl group from secondary to primary hydroxyl was observed in furanosides (ribosides and xylosides) under usual desilylation conditions using tetrabutylammonium fluoride. The migration was studied further on several alkyloxycarbonyl furanosides under either basic or acidic conditions. As follows from ¹³C labelling experiments and product distribution, the migration in xylosides, proceeds intramolecularly via six-membered cyclic carbonate, whereas in ribosides, the migration is intermolecular. Acidic conditions prevented the migration in ribosides whereas the migration in xylosides was circumvented under neutral conditions.     

Total Syntheses of the Chlorinated β‐Carboline Alkaloids Bauerine A,B, and C

The first total synthesis of the chlorinated 1‐oxo‐β‐carboline alkaloid bauerine C based on a Japp–Klingemann reaction is reported. An intermediate of this synthesis was converted to the fully aromatic β‐carboline bauerine B, and the related alkaloid bauerine A was prepared in an analogous manner.     

Direct coupling of magnetic fields to tunneling systems in glasses

We report on investigations of spontaneous polarization echoes in the nonmagnetic multicomponent glass BaO-Al2O3-SiO2 in static magnetic fields. While the echo decay is only marginally influenced, the echo amplitude depends strongly on magnetic fields. It seems that the intrinsic magnetic moment of tunneling systems causes dephasing effects which are detected in our echo experiments. In addition we find a strong increase of the echo amplitude with magnetic fields. This result shows that the coupling of the tunneling systems to magnetic fields is surprisingly strong and cannot be understood on the basis of current theories.     

On the superconductivity of the tin-hydrogen system

Conductivity and superconductivity studies of amorphous [Sn_1–y Cu _y–]_1–x H _x samples in connection with¹¹⁹Sn Mössbauer effect experiments on¹¹⁹Sn_1–x H _x give strong evidence that the observed increase of the superconducting transition temperatureT _c in the Sn–H-system is caused by the stabilization of an amorphous structure. Thus the Sn–H-system is very similar to the Sn–Cu-system and no H-specific effect is needed to explain the increase ofT _c.     

Symmetry-relations and dynamics of molecular crystals in the long wave limit

Symmetry relations for macroscopic constants are derived. Especially it is shown that the Voigt-symmetry holds for the indices of the elastic constants. This has been doubted several times for lattices of particles with additional degrees of freedom. In the second part a simple model for Br₂- and J₂-lattices is discussed. The intermolecular forces are assumed to be van-der-Waals-forces. The influence of the internal degrees of freedom on lattice dynamics is calculated especially for the elastic constants. Further the limiting frequencies forq?0 are given and compared with experimental values.     

Aluminium

Ohne Zusammenfassung     

Molrefraktion elementorganischer Verbindungen, 1. Mitt.: Enileitung. Die Refraktion der Sn−C-Bindung

Zusammenfassung Die Berechnung der Sn–C-Bindungsrefraktionskonstante anhand der Daten von 287 Verbindungen aus 112 Literaturzitaten ergibt die in Tabelle 5 zusammengefaßten Ergebnisse. Bei der Beteiligung eines aromatisch oder konjugiert mehrfachgebundenen Kohlenstoffatoms an der Sn–C-Bindung sind die gefundenen Sn–C-Bindungsrefraktionskonstaten wesentlich höher als im Falle eines primären oder sekundären Alkyl- oder isoliert mehrfach-gebundenen Kohlenstoffatoms.

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Results of the calculation of Sn–C bond refraction constants for 287 compounds, based on data from 112 references, are presented in table 5. Accordingly, Sn–C bond refraction constants appear to be essentially higher for carbon atoms with aromatic or conjugated multiple bonds than for primary or secondary carbon atoms in alkyl groups or carbon atoms with isolated multiple bonds. *** DIRECT SUPPORT *** A3615129 00004

     

Die gleichzeitige photometrische Bestimmung von Thorium und Zirkonium mit Arsenazo III

Ohne Zusammenfassung