Beiträge zur Chemie der Silicium-Stickstoff-Verbindungen, 17. Mitt.: Silylsubstituierte Semicarbazide und Hydrazindicarbonsäurederivate

Zusammenfassung Semicarbazide lassen sich durch Chlorsilane nicht, durch Aminosilane nur unzulänglich substituieren. Man erhält aber Zugang zu der Verbindungsklasse der Silylsemicarbazide wie auch zu Silylhydrazindicarbonsäurederivaten über die Umsetzung von Silylhydrazinen mit Trimethylsilyl-N-cyanat oder mit Phenylisocyanat. Die Verbindungen sind in der Regel außerordentlich hydrolyseempfindlich, sie spalten die Silylgruppen leicht ab und sind nur schwer in völlig reinem Zustand zu fassen. Die Hydrolyseprodukte ermöglichen eine Zuordnung der Struktur der eingesetzten Silylhydrazine im Hinblick auf die Stellung der Silylgruppe am N- oder N-Atom der Hydrazine, da Phenylisocyanat stets nur mit einem an das Stickstoffatom gebundenen H-Atom reagiert.Zugleich 6. Mitt. über Hydrazin-Silicium-verbindungen; 5. Mitt. vgl.⁷.16. Mitt.:J. Pump undU. Wannagat, Mh. Chem.93, 352 (1962).Auszug aus der DiplomarbeitC. Krüger, T. H. Aachen 1960.     

Alkaloid studies—XXX Isolation and constitution of three new Aspidosperma alkaloids: Cylindrocarpine, cylindrocarpidine and pyrifolidine

The isolation and structure elucidation of three new Aspidosperma alkaloids is reported. Cylindrocarpine (II) and cylindrocarpidine (XI) are noteworthy in that they represent analogs of aspidospermine (I) in which the latter's angular ethyl group has been replaced by an angular acetic acid methyl ester function. Furthermore, cylindrocarpine (II) represents the first naturally occurring dihydroindole with a N-cinnamoyl residue. Pyrifolidine (XII) has been shown to be the antipode of O-methylaspidocarpine (XV) and thus bears an enantiomeric relationship at all four asymmetric centers to (-)-aspidospermine (I). Attention is drawn to the possible biogenetic implications of this observation.     

The magnetic structures of HoTiO3 and ErTiO3

The magnetic structures of rare-earth titanium perovskites, ErTiO₃ and HoTiO₃, have been determined at 4.2 K by neutron diffraction. The Er³⁺ moment of (8.5 ± 0.5) μ_B lies along [001] and is colinear with the titanium moment of (-0.7 ± 0.3) μ_B. The Ho³⁺ moment of (8.1 ± 0.5) μ_B is inclined at an angle of 24° to the bc plane and 32° to the ab pla so as to produce an antiferromagnetic ordering of the x component and a ferromagnetic ordering of the y and the z components. The titanium moment of (-0.55 ± 0.3) μ_B lies in the bc plane but its precise direction has not been determined.     

The low temperature electrical properties of some anisotropic crystals

The principal complex dielectric constants have been studied at audio frequencies over the temperature range 5.5–380K for α-quartz, sapphire, magnesium fluoride, and calcite. For some samples, the imaginary part of the dielectric constant revealed the presence of dipolar or thermally activated loss mechanisms which are attributed to trace impurities. The effects of these impurities are considered in arriving at values of the real part of the dielectric constants for each of the materials.     

Crystallographic aspects of the Polymorphism of Silver Chromate and Selenate at high pressures and temperatures

Ag₂CrO₄ II at 25 °C is orthorhombic, space group D-Pnma, with the chrysoberyl structure and a₀, b₀, c₀ = 10.01, 7.01, 5.56 Å. Precipitated Ag₂SeO₄ IV has the thenardite structure. Upon heating to ～600 °C under pressure it transforms sluggishly to Ag₂SeO₄ I, which, upon cooling, then transforms to Ag₂SeO₄ III directly above 8 kbar, or via Ag₂SeO₄ II below 8 kbar. Ag₂SeO₄ III does not easily reconvert to Ag₂SeO₄ IV, and can be quenched to room temperature. It has the same structure as Ag₂CrO₄ II, and the lattice constants a₀, b₀, c₀ = 10.10, 6.95, 5.52 Å. The previously observed transitions in Ag₂SeO₄ at 425 and 537 °C do not involve Ag₂SeO₄ IV and cannot be observed until the IV–I transformation has taken place.     

Rotational relaxation of polar molecules

The method of obtaining rotational energy relaxation times from experimental thermal conductivities using the Wang Chang-Uhlenbeck theory of transport coefficient for polyatomic gases is considered. For polar gases the method turns out to be useful only if serious calculations of the inelastic collisions involved are performed. Using a semiclassical, partly statistical collision treatment the results for the rotational energy relaxation numbers for halogen hydrides taking dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions into account are presented. It is characteristic for the results that hardly any temperature dependence or isotope effects are observed, a behaviour different from earlier investigations.