Structural isomerism of mono- and sesquiterpenoid skeletons

A generator of chemical structures (CONGEN) has been utilized to investigate two aspects of the structural isomerism of mono- and sesquiterpenoid skeletons: (1) the scope of possible isomers under various structural constraints; and (2) the scope of possible isomers based on a mechanistic model which allows interactive exploration of reactions of formation and interconversion. The possibilities, even under severe constraints, are many more than the structural types commonly encountered in natural. These results indicate the potential danger of structural assignment based in part on biogenic grounds.     

Structure in metastable peaks arising from reactions in which[C3H3]+ ions are produced

The metastable peak resulting from the fragmentation of [C₇H₇]²⁺? ions fram a variety of sources shows structure due to the presence of two reactions releasing different amounts of translational energy. The translational energy differences has been measured as 0.52 ± 0.04eV and is thought to be due to the formation of product ions of different structure via competing reactions from a single transition state. The possible structures of these ions are discussed, and it is proposed that the effect observed is due to the formation of [C₃H₃]⁺ ions in two forms, cyclopropenyl and proparg1. The metastable singly charged ions which also lead to product ions of formula [C₃H, ₃]⁺.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. XIV. Untersuchungen über Benzylwolframverbindungen-Darstellung und Charakterisierung des Wolframtetrabenzyls

Contributions to the Chemistry of Transition Metal Alkyl Compounds. XIV. Investigations on Benzyl Tungsten Compounds. – On the Formation and Characterization of Tetrabenzyl Tungsten Unstable benzyl tungsten pentachloride is formed from tribenzyl boron and tungsten hexachloride. Other benzylating agents yield only less defined reduction products. – Reacting WCl₄ · 2 THF with dibenzyl magnesium W(CH₂C₆H₅)₄ can be obtained. The new compound is stable at room temperature and is thoroughly characterized.     

Infrared spectra and rotational isomerism of epifluorohydrin and other propene oxide derivatives

The infrared spectrum for the vapour, liquid and solid states of epifluorohydrin has been studied, and evidence has been obtained for the presence of rotational isomers. The dominant conformer in all phases corresponds to a gauche structure, which was the only form identified in the vapour by microwave spectroscopy [1]. Similar evidence for conformational equilibria has been found for the chloro, bromo and iodo derivatives, and the enthalpy differences between the rotational isomers of these compounds were measured respectively as 4580 ± 970, 3950 ± 400, and 2350 ± 170 J mol^?1 respectively. At low temperatures, epiiodohydrin was found to crystallize in one of two possible crystalline phases. These two phases correspond to the two rotational isomeric conformations of the molecule.     

Schnelle Trennung von Rückstoßprodukten in der Gasphase

Experiments are described in which recoil products are separated fast and selectively. The aim of these investigations is an identification of short-lived nuclides, either for the study of nuclear reactions or for the study of decay properties of new products. The recoil products were provided by a Cf-252 source. The transportation zone and the identification zone could be heated to different temperatures. Using N₂ as carrier gas it was possible to separate Te selectively under certain experimental conditions. When Cl₂ was added, Sb, Tc, Nb, Mo, Zr, Ru and Sn were transported. Transport output was determined in dependence of temperature and composition of the gas.     

Absorption of amines on cation exchange resins

All the amines studied are absorbed in excess of the exchange capacity bysulfonated polystyrene resins from aqueous solutions; the absorption is greatest with benzylamine, whose molecular structure is the closest to that of the monomer of the resin. The absorption is greater, then less the crosslinking of the resin, and it is influenced by the electrostatic field of the resin cations. There is no excess absorption from solvents such as alcohols, acetic acid or dioxane. The absorption characteristics of amines are sufficiently different that separations by elution chromatography on cation exchange resins are possible. Two such separations have been demonstrated. For quantitative analytical use, however, it would be wise to use very fine mesh resins on account of the slowness of diffusion of large amine molecules within the resins.     

Photophysical aspects of single-molecule detection by two-photon excitation with consideration of sequential pulsed illumination.

An important goal in single molecule fluorescence correlation spectroscopy is the theoretical simulation of the fluorescence signal stemming from individual molecules and its autocorrelation function. The simulation approaches developed up to now are based exclusively on continuous-wave (cw) illumination and consequently on cw-excitation. However, this approximation is no longer valid in the case of two-photon excitation, for which pulsed illumination is usually employed. We present a novel theoretical model for the simulation of the fluorescence signal of single molecules and its autocorrelation function with consideration of the time dependence of the excitation flux and thus of all illumination-dependent photoprocesses: two-photon excitation, induced emission and photobleaching. Further important characteristics of our approach are the consideration of the dependence of the photobleaching rate on illumination and the low intersystem-crossing rates of the studied coumarins. Moreover, using our approach, we can predict quantitatively the effect of the laser pulse width on the fluorescence signal of a molecule, that is, the contributions of the photobleaching and saturation effects, and thus we can calculate the optimal laser pulse width. The theoretical autocorrelation functions were fitted to the experimental data, and we could ascertain a good agreement between the resulting and the expected parameters. The most important parameter is the photobleaching constant sigma, the cross section of the transition Sn<--S1, which characterises the photostability of the molecules independent of the experimental conditions. Its value is 1.7 x 10(-23) cm2 for coumarin 153 and 5 x 10(-23) cm2 for coumarin 314.     

Neue Wege und Ergebnisse der Röntgenspektroskopie

Zusammenfassung Es wird eine Röntgenröhre mit Durchstrahlanode zur bequemen Außenanregung von Röntgenspektren beschrieben. Mit ihrer Hilfe konnte die Frage der sekundären Erregung des ₃-Satelliten im Falle des Chroms geklärt werden. Ferner eignete sich die Röhre zusammen mit vielkristallinen Beugungsgittern gut für ein einfaches spektralanalytisches Verfahren der Elemente Ti (22) bis Zn (30). Schließlich konnte gezeigt werden, daß man bei Verwendung vielkristalliner Beugungsgitter unter Ausnützung bekannter Gesetzmäßigkeiten unter Umständen eine Genauigkeit der Wellenlängenmessung erreicht, die jene mit klassischen Einkristallspektrographen übliche übertrifft. Diese hohe Genauigkeit reicht aus, die geringfügigen Einflüsse chemischer Bindung auf dieK ₁-Linie von Eisen und Kobalt meßbar zu machen.

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Summary A röntgen tube is described with a radiating anode for the convenient external excitation of röntgen spectra. With its aid, it was possible to explain the problem of the secondary activation of the ₃-satellites in the case of chromium. Furthermore, the tube was well suited for use, in conjunction with multicrystalline diffraction gratings, for a simple spectral analytical procedure for the elements Ti (22) up to Zn (30). Finally, it could be shown that with use of multicrystalline diffraction gratings and employment of known regularities, it is possible to attain an accuracy of the measurement of the wave length exceeding that secured with the classic monocrystal spectrograph. This high accuracy is sufficient to bring into the range of measurement the slight influences of chemical binding on theK ₁-line of iron and cobalt.

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Résumé On décrit un tube à rayonsX avec une anode rayonnante pour l'excitation externe des spectres de rayonsX. En employant ce tube il est possible de résoudre le problème de l'excitation secondaire des satellitesa ₃ dans le cas du chrome. En outre, ce tube convient très bien pour être employé avec des réseaux de diffraction à cristaux multiples; on a ainsi un procédé simple d'analyse des éléments du titane (22) au zinc (30). Finalement on a pu montrer qu'en employant des réseaux de diffraction à cristaux multiples et à partir de régularités connues, on peut atteindre une précision dans la mesure des longueurs d'onde qui dépasse celle qu'on atteint habituellement avec un spectrographe à cristal unique. Cette précision élevée suffit pour qu'on puisse mettre en évidence la faible influence de la liaison chimique sur les raiesK ₁ du fer et du cobalt.

     

Eine neuc Umlagerung an einem Metathebainon-Derivat mit Cyclohexa-2,5-dienon-Struktur

Zusammenfassung 4-O-Methyl-7,8-dehydro-metathebainon-methin (1) geht in alkalischer Lösung in das Naphthalin-Derivat3 über, das unter Abspaltung von Formiat7 liefert. Das Auftreten von3 kann durch Isolierung von13a nach Reduktion mit NaBH₄ nachgewiesen werden. Die aus3 und7 durch Reduktion erhaltenen Alkohole8a und13a werden in saurer Lösung unter Methanol-Abspaltung zu den 2,3-Dihydro-naphtho[1,8-bc]pyranen9 und14 cyclisiert.

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A new rearrangement of a metathebainone derivative with a cyclohexa-2,5-dienone groupment

4-O-Methyl-7.8-dehydrometathebainonemethine (1) in alkaline solution rearranges to the naphthalene derivative3, which eliminates formiate to give7. The occurrence of3 was confirmed by isolation of13a after reduction with NaBH₄. The hydroxy compounds8a and13a, obtained by reduction, eliminate methanol and cyclize to the 2.3-dihydronaphtho[1.8-bc]pyrans9 and14.

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Mit 2 Abbildungen     

Radiolysis of aqueous solutions of cobalt(II) and cobalt(III)

Radiolysis of aqueous solution of di and trivalent cobalt with 1:2 (bis) carboxymethylaminodiethyltetraacetic acid (EGTA) was investigated, both in absence and in presence of oxygen. A radiolytic mechanism has been proposed. It has been shown that the degradation at the ligand of the chelate is due to OH only.