Transitivität und Homogenität projektiver Ebenen

Ohne Zusammenfassung     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. XVIII. Darstellung und Eigenschaften von Vanadintetrabenzyl und von Benzyltantalchloriden

Contributions to the Chemistry of Transition Metal Alkyl Compounds. XVIII. On the Preparation and Properties of Tetrabenzyl Vanadium and Benzyl Tantalum Chlorides Pure tetrabenzyl vanadium was isolated and characterized by elementary analyses, EPR and ¹H-NMR spectra, by hydrolysis and thermal decomposition. — Experiments for the preparation of tetra or pentabenzyl compounds of niobium and tantalum failed, but we could prepare C₆H₅CH₂TaCl₄, (C₆H₅CH₂)₂TaCl₃, and (C₆H₅CH₂)₃TaCl₂, the last two in form of bipyridyl complexes.     

Role of para-substituted phenols in curing resole-type phenolic resins

Certain para-substituted phenols, namely, those phenols without ortho substituents and containing an electron-attracting atom or group in the para position, e.g. p-nitro-, p-bromo-, and p-chlorophenol, hasten gelation of etherified phenolic resoles. A mechanism involving cleavage of dibenzyl ether linkages in these resins is proposed to explain gelation.     

Partial methylation of quercetin: Direct synthesis of tamarixetin,ombuin and ayanin

Methylalion of the penlahydroxy flavone, quercetin, was observed to proceed in distinct stages. From the reaction mixture (methyl sulfale/potassium carbonate/acetone), the isolation of three major intermediates, a mono-, a di- and a trimethyl ether and their identification as the naturally occurring ethers: tamarixelin, ombuin and ayanin is described.     

Hydrogen absorption in Zr(AlxB1−x)2 (BFe,Co) laves phase compounds

The hydrogen absorption capacity of the systems Zr(Al_xFe_1?x)₂ and Zr(Al_xCo_1?x)₂ (0? x ?1) was measured at hydrogen pressure of 70 atm and room temperature and at 40 atm and liquid nitrogen temperature. The two systems present very interesting and unexpected results.A dramatic rise in the hydrogen capacity occurs for small x values similar to previous results for the systems Zr(A_xB_1?x)₂ (A  V, Cr, Mn; B  Fe, Co; 0?x?1). The maximum hydrogen content in both systems is achieved for x ≈ $\text{2}\text{12}$ at 40 atm and 80 K. Further increase of the Al content leads, however, to a steep decrease in the hydrogen capacity. This general behaviour is well described by a phenomenological model, recently proposed by us, and thus supporting the importance of short-range neighbouring effects for the hydrogen absorption capacity. The influence of Al on the hydrogen sorption properties in different intermetallic compounds is discussed.     

Subharmonic non-linear acoustic resonances in closed tubes

Summary A closed tube is considered driven at one-half of the fundamental frequency. The interesting fact appears that acoustic theory breaks down in the inviscid case. At a sufficient intensity of a first resonant overtone, the theory of Chester applies.

---

Zusammenfassung Betrachtet wird ein geschlossenes Rohr, das bei ber halben Resonanz-frequenz angetrieben wird. Es ergibt sich die bemerkenswerte Tatsache, dass die akustische Theorie im reibungsfreien Fall ihre Gültigkeit verliert. Bei genügend grosser Amplitude eines ersten Obertones ergibt sich die Theorie von Chester.

     

A kinetic study of the reaction between di-h5-cyclopentadienyltungsten dihydride and benzotrichloride

The reaction of di-h⁵-cyclopentadienyltungsten dihydride with benzotrichloride proceeds to produce as the only observed products di-h⁵-cyclopentadienyltungsten dichloride and benzal chloride. The reaction was shown to be first order with respect to Cp₂WH₂. The relative rate of reaction increases substantially with the use of 3,4-dichlorobenzotrichloride in place of benzotrichloride as the oxidizing agent.