Die elektrische Zerstäubung von Silicium in Aceton

Zusammenfassung Die Bildung kolloider L?sungen durch Hochspannungskurzschlu\funken zwischen kleinen Siliciumstücken in Aceton unter sauerstoffreiem Stickstoff wird untersucht: sowohl die Ver?nderungen der Siliciumoberfl?chen durch das kurzzeitige Schmelzen und Verdampfen des Siliciums, als auch die chemischen Eigenschaften der in L?sung befindlichen Kolloide. Das Interesse war nicht, wie bei der Svedbergschen Kolloidzerst?ubung, auf die Methode zur Herstellung kolloider Metalle, in diesem Falle kolloiden Siliciums, gerichtet, sondern auf die chemische Umsetzung des Siliciums unter den gegebenen extremen Temperaturbedingungen mit dem Aceton zu kolloiden Siliciumverbindungen. Durch fraktioniertes Zentrifugieren und Eindampfen der Restl?sung ist die kolloide L?sung der Siliciumverbindungen in 3 Anteile zerlegt worden: Ein braunes Pulver, schwarze Flocken und ein dem Silikagel ?hnliches Gel. Die 3 Substanzen enthielten alle Si, O, C und H in Form einer anorganischen Si-O-haltigen Komponente und einer unges?ttigten Kohlenwasserstoffkomponente. Je gr?\er der Anteil der organischen Komponente ist, desto kleiner und l?slicher sind die Kolloidteilchen in Aceton. Die Struktur der Gelteilchen ist sehr labil und geht unter Verglimmen in eine stabilere aber nicht kristalline über. Dieser Vorgang findet beim Erw?rmen, auch unter vollkommenem Ausschlu\ von Sauerstoff, statt. Das Gel l?st sich in Laugen und flockt wieder mit S?uren. Das ganze Verhalten, einschlie\lich der analytischen Befunde, l?\t darauf schlie\en, da\ die hier erhaltene kolloide L?sung, aber auch das Svedbergsche Siliciumsol nicht kolloides elementares Silicium enthalten, sondern Kolloidteilchen, die silikonharzartigen Charakter besitzen. Hans Kautsky Jun. Diss. (Marburg 1954). Mein Vater, Prof. Dr. Hans Kautsky, regte mich zu dieser Arbeit an und gab mir wertvolle Ratschl?ge; ich danke ihm herzlich dafür. Herrn Dr. E. Hellner vom mineralogischen Institut der Philipps-Universit?t Marburg/Lahn, der die R?ntgenuntersuchungen unserer Substanzen vorgenommen hat, sei an dieser Stelle auch vielmals gedankt. Zu besonderem Dank bin ich der Deutschen Forschungsgemeinschaft für die apparative Unterstützung der Arbeit verpflichtet, der Firma Rosenthal-Isolatoren Gesellschaft m. b. H., Selb, für die kostenlose überlassung der Kondensatorbatterie.     

Photocycloaddition of Cyclohex‐2‐enones to Penta‐1,2,4‐triene

Dihydrothiinone 9a undergoes photocycloaddition regioselectively to all three C?C bonds of penta‐1,2,4‐triene ( 10 ), the relative stabilities of the biradical intermediates determining the product distribution. In contrast, cyclohexenone 9b and dihydropyranone 9c afford more complex mixtures of bicyclo[4.2.0]octanones, which also turn out to be less stable on chromatographic workup, reflecting the higher strain due to the shorter bond lengths (C? O and C? C vs. C? S) in the six‐membered rings, respectively.     

Säurekatalysierte Umlagerungen von 1,5-Dimethyl-6-methyliden-tricyclo[3.2.1.02,7]oct-3-en-8endo-olen

Acid Catalysed Rearrangement of 1,5-Dimethyl-6-methyliden-tricyclo[3.2.1.0^2,7]oct-3-en-8endo-ols The tricyclic alcohols 2,3,4 and 6 (Scheme 1) are synthesized by the reaction of the tricyclic ketone 1 with sodiumborohydrid or metalloorganic reagents. Their configuration at C(8) is determined by NMR. in the presence of Eu(fod)₃. The exo-attack of 1 by the nucleophil forming the endo-alcohol is favored, the π-electrons of C(3) = C(4) hindering the endo-attack. On treatment with sulfuric acid in dioxane/water at 25° the tertiary alcohols yield aryl-substituted ketones. 3 gives in 78.5% yield a mixture of the 3-(dimethylphenyl)-2-butanones 12 and 13 , in addition to 16.5% of (2,3,4-trimethylphenyl)-2-propanon ( 14 ) (Scheme 2). The alcohols 4 and 6 yield mixtures of the 2-(dimethylphenyl)-3-pentanones 19 and 20 (72%), and 2-(dimethylphenyl)-propiophenones 21 and 22 (68%), respectively (Scheme 2). In the case of the secondary alcohol 2 mainly products derived from hydration at the C(6), C(9) double bond are formed, namely the mixture of diols 23 and 24 (21%), and the mixture of the isomeric 2-(dimethylphenyl)propanals 25, 26 and 27 (3%) (Scheme 3). - The structures of 12–14, 19/20, 21/22, 23/24 and 25/26/27 were established by spectroscopic data. In the case of 12 and 13 the degradation of their mixture to the known 1-(dimethylphenyl)ethanols 17/18 confirmed the assignment. - The most probable mechanism for the rearrangement of 3 is shown in Schemes 4 and 5. The reaction proceeds from 3 through a, b and g to 12 and 13; 14 is formed via e, f and i . In the case of 4 and 6 only the reaction analogue to 3 → a → b → g ?12/13 takes place. The isomeric aldehyds 25–27 formed from 2 could have the structures s, t , and v . The former two could be generated in a similar way as 12/13 from 3 , the latter one as shown in Scheme 8.     

Über die Carotinoide Flavoxanthin und Chrysanthemaxanthin: 1H-NMR.-, 13C-NMR.- und Massen-Spektren und absolute Konfiguration. (Kritische Überprüfung veröffentlichter chemischer und physikalischer Daten)

On the Carotenoids Flavoxanthin and Chrysanthemaxanthin: ¹H-NMR., ¹³C-NMR. and Mass Spectra, Absolute Configuration, Survey of Published Data Very pure flavoxanthin ( 1 ) and chrysanthemaxanthin ( 2 ) have been reisolated from flower heads of Taraxacum officinale. Both compounds were characterized by chromatographic, chemical and chiroptical data and extensive NMR. measurements. Examination of many published data on 1 and 2 led to the conclusion that flavoxanthin has often been mistaken for chrysanthemaxanthin and vice versa. Chemical degradation of 1 and 2 to (?)-loliolide ( 5 ) coupled with NMR. evidence (ASIS, spin-decoupling, NOE) allowed the assignment of the absolute configurations of 1 and 2 . Thus (+)-flavoxanthin is (3S,5R,8R, 3′R,6′R)-5, 8-epoxy-5, 8-dihydro-β, ε-carotene-3, 3′-diol and (+)-chrysanthemaxanthin its C(8)-epimer.     

Field desorption mass spectrometry of 1-methylpyridinium salts

Quaternary pyridinium salts were investigated by field desorption, field ionization and electron impact mass spectrometry. Thermal decomposition of the salts under field desorption conditions was found to give very abundant volatile products, identified as the dihydro analogues and the ‘methides’ of the cations. The formation of the volatile compounds, especially those with molecular weights corresponding to those of the (cation ?1), (cation +1) and (cation +13) was studied in detail by deuterium and ¹³C labelling experiments.     

Reaktionen von 2- und 3-phenylsubstituierten Alkylakyliden-iminium-Ionen in der Gasphase. 5. Mitteilung über stossinduzierte Fragmentierungen von felddesorbierten Kationen

Reactions of 2- and 3-Phenyl Substituted Alkylalkylidene Iminium Ions in the Gas Phase The collision-induced fragmentations of 2- and 3-phenyl substituted alkylalkylidene iminium ions are reported. Besides the homolytic cleavage of the azaallyl bond a nucleophilic attack of the unsubstituted phenyl group at the iminium function is observed in the gas phase, yielding carbonium ions such as cyclopropanspirobenzenium ( 3 ), indanylium ( 10 ) and indenylium ions ( 11 ).     

Konstitution und absolute Konfiguration der Rhoeadin-Alkaloide (+)-Alpinigenin und (+)-cis-Alpinigenin

The constitution and absolute configuration of the rhoeadine alkaloids (+)-alpinigenine and (+)-cis-alpinigenine. The fundamental structure of the hemi-acetal phenylbenzazepine alkaloid (+)-alpinigenine ( 1 ), isolated from Papaver bracteatum LINDL ., was derived essentially from ¹H-NMR.- and mass-spectra of 1 and its derivatives 7, 10 and 14 (cf. Scheme 2). The positioning of the four methoxy groups in the two aromatic rings could be deduced from the ¹H-NMR.-spectra of the N-oxides 14 and 15 in which, as a result of favourable sterical and conformational behaviour, an interaction exists between the N-oxide oxygen atom and one of the two ortho protons in ring C. The B/D-trans-fused 1 undergoes isomerization in 1N HCl to cis-alpinigenine ( 16 ). A stereochemical correlation between bases in the trans-and cis-series was enabled via an Emde degradation of the corresponding methylacetal-methyliodides 21 resp. 19 leading to the enantiomeric isochroman derivatives 22 resp. 23 which are achiral at C (2) (Scheme 4). The configuration at C (14) in the hemi-acetals (eg. 1 and 16 ) and the methyl ethers (eg. 7 and 8 ) is discussed in detail (cf. Scheme 7). (+)-Alpinigenine ( 1 ) has the (1S, 2R, 14R) configuration and (+)-cis-alpinigenine ( 16 ), in chloroform or acetone solution, the (1R, 2R, 14R) configuration.     

Stereochemistry of Polynuclear Cadmium(II)thioglycolates: Crystal Structure of [ICd8(SCH2CH2OH)12]3+ · 3I− · H2O

Crystals of the title compound are triclinic, a = 27.87 Å, b = 10.77 Å, c = 12.94 Å, α 73.1°, β 116.1°, γ 120.0°, space group P1 . The structure consists of octanuclear ions: Eight Cd(II) ions are found at the corners of a distorted cube, the center of the cube is occupied by an iodide, the twelve thioglycolate sulfur atoms bridge the twelve edges of the cube thereby forming a distorted icosahedron. Cadmium ions are either five or seven coordinate. The phase problem for this structure was solved using a combination of very high and very low E-values.     

Inverse Pulspolarographie am h?ngenden Quecksilbertropfen

Zusammenfassung Die inverse Voltammetrie am hängenden Quecksilbertropfen mit pulspolarographischer Aufzeichnung der anodischen Auflösungsströme wird auf ihre Leistungsfähigkeit untersucht. 10^–9 M Lösungen von Cu, Pb, Cd, Zn können im Routinebetrieb analysiert werden. In Alkalisalzmatrices sind Direktbestimmungen der Schwermetalle im 10^–7 bis 10^–8%-Bereich möglich. Die Nachweisgrenze für Cd beträgt 5 · 10^–11 Mol/l. Die Empfindlichkeit der Methode wird mit derjenigen verwandter voltammetrischer Verfahren verglichen.

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Anodic stripping pulse polarography at the hanging mercury drop electrodeDetermination of Cu, Pb, Cd and Zn

The efficiency of anodic stripping pulse polarography at the H.M.D.E. is tested. In routine work the analysis of 10^–9 M solutions of Cu, Pb, Cd, Zn offers no difficulty. The determination of the elements in alkali salts in the 10^–7 to 10^–8% range is possible. The detection limit for Cd was found to be 5×10^–11 M. The sensitivity of the method was compared with those of related voltammetric techniques.