Die Koordination von Ni2+ und Co2+ in Lösung von N,N-Dimethylacetamid

PMR spectra were obtained from bulk solvent molecules in anhydrous solutions of [M(DMA) ₆](ClO₄)₂ (M=Co, Ni) in N,N-dimethylacetamid (DMA). The free enthalpy of activation G _c ^* increases with increasing amount ofM ²⁺ as a result of the coordination of the cationsvia the oxygen atom resulting in a decrease of the bond length. Cobalt(II) acts as a weaker electron pair acceptor than nickel(II). The oxygen coordination is also shown by the different line broadening of the C-methyl protons as compared to that of the N-methyl protons.

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Mit 6 Abbildungen     

Couche limite tridimensionnelle

Zusammenfassung Es handelt sich um die Grenzschicht an einer schraubenf?rmigen Platte bei gleichf?rmigem Eindringen in eine Flüssigkeit, sowie um die Grenzschicht in einer Flüssigkeit bei Umstr?mung einer schraubenf?rmigen Platte. In beiden F?llen würde die Bewegung einer reibungslosen Flüssigkeit durch die Platte nicht ge?ndert werden; durch die Reibung entstehen aber Grenzschichten. Das Verfahren gibt keine laminare Abl?sung; doch handelt es sich dabei nur um eine Vermutung, die aber um so wahrscheinlicher ist, je gr?sser bei gegebener Randneigung das Seitenverh?ltnis der Platte ist.

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Communication au Congrès de la GAMM à Hambourg (23–27 avril 1957).     

Cycloisomerization of dienes with carbophilic lewis acids: mimicking terpene biosynthesis with Pt(II) catalysts

[reaction: see text]. Dicationic Pt(II) complexes containing triphosphine pincer ligands are excellent catalysts for the cycloisomerization of 1,6- and 1,7-dienes into bicyclopropane carbocycles. In analogy to the biosynthetic route to these monoterpene-like compounds, carbocation intermediates are proposed and supported by trapping experiments. Reactivation of the trapped intermediates indicates that cation generation by C-C bond formation is both rapid and reversible.     

MOLGEN-CID--A canonizer for molecules and graphs accessible through the Internet

The MOLGEN Chemical Identifier MOLGEN-CID is a software module freely accessible via the Internet. For a molecule or graph entered in molfile format (2D) it produces, by a canonical renumbering procedure, a canonical molfile and a unique character string that is easily compared by computer to a similar string. The mode of operation of MOLGEN-CID is detailed and visualized with examples.     

Adhesion between Epoxy-Polysulfone Blends and Fibers

The adhesive strength of a fiber-polymer interface is determined, where epoxy resin blends and linear heat-resistant thermoplastics - polysulfone (PSF) and polyetherimide (Ultem) - are used as matrices. Steel wire and polyamide (nylon-6) fibers are taken as reinforcing fillers. It is shown that the addition of PSF to epoxy resin results in a maximum on the concentration curve corresponding to a 10% PSF content. It is also found that the adhesive strength of the ED-20+Ultem-steel wire interface is practically independent of the modifier content under low (up to 10%) Ultem concentrations.     

Cataloging graphs by generating them uniformly at random

We describe an algorithm for cataloging graphs by generating them uniformly at random. The method used is based on a recent algorithm by Dixon and Wilf that generates orbit representatives uniformly at random. The approach is refined to graphs with prescribed numbers of edges and vertices, and then applied to obtain the complete list of graphs on 10 vertices.