Massenspektrometrie von Silylpyrazolen—I: Isomere Trimethylsilylpyrazole

By a comparison of the mass spectra of mono-, bis- and tris(trimethylsilyl)pyrazole isomers, characteristic influences of the different TMS-groups are revealed. An N-TMS-group forms an ion of mass 72 in the spectrum of N-TMS-pyrazole and with more than one TMS-group present, leads to the expulsion of a neutral fragment C₃H₈Si. Decomposition of the 4-TMS-group is more facile than the others, giving rise to a small molecular ion of intensity (approx.) 5%Σ₄₀. In N-silylated pyrazoles without a 4-TMS-group, intensive elimination of HCN from the [M ? CH₃˙]⁺ ion can be assigned to an unsubstituted C-3 position. In the case of unsymmetrically substituted pyrazoles without and N-TMS-group, silylation by an N-TMS acetamide may help to identify the predominating tautomer.     

Benchmarking of ruthenium initiators for the ROMP of a norbornenedicarboxylic acid ester

The kinetic study of ring-opening metathesis polymerization (ROMP) of a diester functionalised norbornene derivative, (±)-exo,endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid diethyl ester, with a series of ruthenium benzylidene complexes revealed the applicability of these initiators for well defined polymerization reactions. Values for the rate of initiation as well as the rate of propagation of the initiators were determined and correlated to the molecular weight and polydispersity of the isolated polymers. As the only initiator providing an entry to virtually monodisperse polymers the classical “first generation Grubbs-catalyst” was identified, while N-heterocyclic carbene based initiators polymerized with a rate of propagation much higher than the rate of initiation yielding polymers with a broader molecular weight distribution.     

Perturbational analysis of the regioselectivity in the acrolein dimerization

Using intermolecular SCF-perturbation theory, the controlling factors determining the regioselectivity in the acrolein dimerization are derived by a rigorous decomposition of the interaction energy. This partitioning of the interaction energy is performed up to a level where a comparison with frontier orbital models is possible. The regioselectivity is found to be determined by orbital interactions occuring via the terminal atoms and atoms involved in secondary Woodward-Hoffmann interactions.     

Zur kritischen Lösungstemperatur einiger Systeme mit zweibasischen organischen Säuren

Zusammenfassung Fischers Methode der Mikrountersuchung der kritischen Mischungs-temperatur hat grundsätzlich neue Wege in der Analyse binärer und ternärer Flüssigkeitsgemische eröffnet.In dieser Arbeit wurde versucht, für die homologe Reihe: Oxalsäure-Malonsäure-Bernsteinsäure durch Ermittlung der Mischungslückendiagramme Zusammenhänge zwischen den beim sogenannten 'Makroversuch und den bei der Mikrobestimmung auf dem Kofler-Heiztisch herrschenden Verhältnissen aufzuzeigen und gleichzeitig eine brauchbare Schnellmethode für die Bestimmung wässeriger Lösungen der untersuchten Säuren zu finden.Weiters wurden die Unterschiede, die sich zwischen den Maximalwerten der Mischungslückendiagramme, ihren volumgleichen Temperaturwerten und den Werten der auf dem Heiztisch gefundenen Mikroeichkurve experimentell erfaßt und diskutiert.Es sei besonders im Falle der Oxalsäure auf die obgenannten Unterschiede hingewiesen. Im Schaubild sieht man die Eichkurve nachFischer als Gerade, um die herum sich die Werte der Maxima und die volumgleichen Werte sozusagen als 'periodische Funktionen legen. Diese Werte sind also nicht immer eindeutige Funktionen der Konzentration der betreffenden Lösung. Die Temperaturwerte des Mischungsverhältnisses 50 50 (die ja für die Aufstellung analytisch brauchbarer Eichkurven überhaupt als einzige in Betracht kämen) wurden übrigens bei der Anilinpunktbestimmung zur Prüfung von Kraftstoffen praktisch verwertet¹³. Die Mikrobestimmung in der Kapillare ist wegen der an anderer Stelle besprochenen Vorzüge jedem Makroverfahren überlegen.

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Summary Fischer's method of micro investigation of the critical mixing temperature has revealed completely new ways in the analysis of binary and ternary mixtures of liquids.By determining the miscibility gap diagram, attempts were made to discover the connections between the so-called macro-trial and the microdetermination using the Kofler heating stage, and at the same time to discover a rapid method for determining aqueous solutions of the acids under investigation, which belonged to the homologous series: oxalic, malonic, succinic acids.Furthermore, the differences which were found between the maximal values of the miscibility gap diagram, their volume-equal temperature values, and the values of the micro calibration curve found on the heated stage were discussed.Special emphasis is given to these differences in the case of oxalic acid. In the diagram, the calibration curve afterFischer appears as a straight line about which are situated the values of the maxima and the volume-equal values so-to-say as periodic functions. These values are not always therefore unequivocal functions of the concentration of the solution in question. The temperature values of the miscibility ratios (5050), which in fact are the only ones that could be considered in the construction of analytically usable calibration curves, were also evaluated in practice in the determination of the aniline point for testing motor fuels¹³. Because of the advantages discussed elsewhere, the micro determination in a capillary is superior to any macro method.

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Résumé La méthode deFischer de microdéterminations de la température critique de mélange a ouvert de nouvelles voies fondamentales à l'analyse des mélanges liquides binaires et ternaires.Dans le travail présenté l'auteur cherche à montrer, pour la série homologue acide oxalique, acide malonique, acide succinique, par l'établissement des diagrammes de discontinuité des mélanges, les relations existant entre les conditions de la «macrodétermination» et celles de le microdétermination avec le banc chauffant de Kofler; simultanément il s'efforce de mettre au point une méthode rapide de dosage des solutions aqueuses des acides considérés.Par ailleurs il a mis en évidence et discuté les différences qui se manifestent expérimentalement entre, d'une part, les valeurs maxima des diagrammes de discontinuité des mélanges et les valeurs des températures à volume constant et d'autre part les valeurs trouvées pour la courbe de micro étalonnage sur banc chauffant.L'auteur a particulièrement étudié ces différences dans le cas de l'acide oxalique. Sur la figure on voit que la courbe d'étalonnage d'aprèsFischer est une droite tandis que les valeurs des maxima et les valeurs des températures à volume constant se présentent comme des fonctions «périodiques». Il en résulte que ces valeurs ne sont pas toujours des fonctions univoques de la concentration de la solution considérée. Les valeurs de la température pour le rapport de mélange 50/50 (qui pour l'établissement de courbes d'étalonnage utilisables en analyse doivent être exclusivement frites en considération) ont été en outre pratiquement utilisées pour le contrôle de la détermination du point d'aniline de carburants¹³. La microdétermination en capillaire, du fait d'avantages qui sont décrits dans une autre publication, est supérieure à toute macro-technique.

     

Synthesis,renal vasodilator and dopamine-sensitive adenylate cyclase activities of O-Methyl derivatives of 6-chloro-2,3,4,5-tetr ahydro-1-(4-hydroxyphenyl)-1H-3-benzazepin-7,8-diol (SK&F 82526)

The three possible mono-O-methyl derivatives of 6-chloro-2,3,4,5-tetrahydro-1-(4-hydroxyphenyl)-1H-3-benzazepin-7,8-diol (SK&F 82526) ( 1 ) have been synthesized to facilitate the isolation and characterization of metabolites of this compound and for biological testing. The syntheses generally involved preparation of appropriately substituted benzaldehydes, conversion of these to phenylacetic acids and use of these to N-acylate arylethanolamines. The phenylacetamides thus formed were reduced to amines and these were deprotected and cyclized to the desired final products. In one case deprotection followed cyclization. These compounds were tested as activators of dopamine-sensitive adenylate cyclase (a measure of DA-1 agonist activity) and as renal vasodilators. All three O-methyl derivatives were much less potent than 1 in cyclase activation and as renal vasodilators. Weak inhibition of adenyl cyclase was also observed for all three compounds and one showed weak renal vasoconstrictor activity. Preliminary investigation of the metabolism of 1 disclosed that two of the three monomethoxy compounds were formed in trace amounts in the rat and the dog. In a related investigation, the trimethoxy derivative of 1 was subjected to acid-catalyzed hydrolysis conditions. The relative ease of cleavage of methoxy groups was 7 > > 4′ > 8.     

The efficiency of light-emitting electrochemical cells

We report on the efficiency behavior of light-emitting electrochemical cells (LECs) fabricated from a methyl-substituted ladder-type poly(p-phenylene) (mLPPP) that was blended with a crown ether based solid state electrolyte. Unlike organic light-emitting diodes (oLEDs) utilizing mLPPP as an active layer, the LECs suffer from a loss of efficiency at elevated current densities. From scan rate dependent studies we deduce that this efficiency drop is not only due to device decomposition upon high voltage operation and we also reveal the intrinsic mode of LEC operation. The decreasing width of the intrinsic region between the p- and n-type doped zones upon ongoing pin-junction formation causes distinct (either field or electrode induced) luminance quenching effects.     

Influence of solvent polarity upon salt solubilities,II: Solubilities of two potassium carboxylates at 85°C in aqueous 1,4-dioxane

The solubilities of potassium acetate and benzoate in aqueous 1,4-dioxane at a temperature of 85°C are reported together with a quasi-thermodynamic general treatment of the experimental results.This brief contribution is a second report upon the results of systematic solubility measurements, commenced with Ref.¹, which have been performed by Dr.John A. McNaney during his abruptly truncated lifetime.     

The electron impact fragmentation of 3- and 4-styrylpyridazine

The electron impact mass spectrometric fragmentation of trans-3- and trans-4-styrylpyridazine is reported in detail, including a comparison with other aza-stilbenes. With regard to a distinction between the two isomeric styrylpyridazines, the intensity ratio of the M⁺ and [M-1]⁺ ions, the general degree of fragmentation and the elimination pathways of nitrogen proved to be most characteristic.