NMR spectroscopy of metal cyclopentadienyls VIII. Prototropism and dimerisations of silicon cyclopentadienyls

Studies have been made of the slow dynamic processes which occur with the silicon cyclopentadienyls C₅H₅Si(CH₃)Cl₂, such as prototropic rearrangement and dimerisation. The product formed through spontaneous dimerisation has been found to consist almost entirely of the dimer of the main vinylic isomer of C₅H₅Si(CH₃)Cl₂. The dimeric structure has been proved by means of PMR spectra (100 MHz). From kinetic studies values of the rate constants at temperatures of 20,44,55, and 65° have been obtained and an approximate plot of log kvs. (1/T)x10³, has enabled the thermodynamic characteristics of the prototropic rearrangement and of the dimerisation to be calculated. The ability of cyclopentadienyl systems to undergo hydrogen migration is discussed and the reactivity of fluxional systems is shown to be governed by the rate of metallotropic rearrangement.     

Influence of electronegative substituents on the electronic spectra of the porphyrins in the form of dications

The positions of the electronic absorption bands and also the intensities of the Soret bands of the porphyrins with ethoxycarbonyl substituents in the form of dications have been calculated by the LCAO MO method in Huckel's approximation. Comparison with the experimental results shows good agreement.     

Untersuchung der Temperaturabhängigkeit derg ik -Tensoren von Polyäthyleneinkristallen

Zusammenfassung Es wurden die Kristallitgröße und die Änderungen der parakristallinen Gitterstörungen aus den Linienbreiten des Röntgenweitwinkeldiagramms von lösungskristallisiertem linearem Polyäthylen bei den Temperaturen 15°K, 73°K, 173°K und Zimmertemperatur bestimmt. Es wurde eine Zunahme der Gitterstörungen mit fallender Temperatur gefunden.

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Summary The crystallite size and the paracrystalline distortions in polyethylene single crystals were evaluated by the measurement of the linewidth in the X-ray wide angle diagram at four different temperatures (15°K, 73°K, 173°K and 297°K). An increase of the lattice distortions with decreasing temperature was found.

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Mit 3 Abbildungen

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Vorgetragen auf der Arbeitssitzung des Fachausschusses Physik der Hochpolymeren in der Frühjahrstagung 1970 des Regionalverbandes Hessen-Mittelrhein-Saar der Deutschen Physikalischen Gesellschaft in Darmstadt, 10.–13. März 1970.     

Coalescence in three-phase fluid systems

Summary The gravity coalescence of drops at flat fluid/liquid interfaces was studied in three-phase systems. Rest-time distributions were in qualitative agreement with the earlier theory of Charles and Mason for two-phase systems. The probability of coalescence increased inversely with the square of intervening film thickness. Partial coalescence was similar to that previously observed in two-phase systems. The viscosity of the drop affected the mechanism of coalescence more than the viscosities of the other phases.

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Zusammenfassung Es wurde die Koaleszenz von Tropfen an ebenen Flüssigkeits-Flüssigkeitsgrenzfl?chen in Dreiphasensystemen untersucht. Die beobachtete Verteilung der Verweilzeiten ist in qualitativer übereinstimmung mit der Theorie von Charles und Mason für Zweiphasensysteme. Die Wahrscheinlichkeit dafür, da? Koaleszenz auftritt, nimmt umgekehrt proportional mit dem Quadrat der Filmdicke zwischen Tropfen und Phasengrenze zu. Die partielle Koaleszenz war ?hnlich, wie sie früher in Zweiphasensystemen beobachtet worden war. Die Viskosit?t des Tropfens beeinflu?t den Mechanismus der Koaleszenz mehr als die Viskosit?t der anderen Phasen.

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Oxidation of the [Rh(CO)2Cl2] anion in aqueous solution

The reaction of rhodium(I) carbonyl chloride, [Rh(CO)₂Cl]₂, with dichromate, cerium(IV) sulfate, hexachloroplatinic acid or p-benzoquinone in aqueous hydrochloric acid proceeds by consumption of 4 equivalents of oxidizing agent per mole or rhodium(I) in accordance with the equation Rh^I(CO)₂  4e + H₂O → Rh^III(CO) + 2H⁺ + CO₂A “cyclic” oxidation mechanism is suggested.     

1,2-oxazine chemistry—II : The crystal and molecular structure of N-(p-carboxybenzyl)-tetrahydro-1,2-oxazine

The crystal structure of the title compound has been determined from X-ray diffractometer data by direct methods, and refined by full matrix least squares techniques to R = 0·057 for 1231 reflections. The crystals are monoclinic, space group C2/C, cell dimensions a = 1665, b = 987, c = 1443 pm, β = 107·37° and Z = 8. The conformation of the tetrahydro-1,2-oxazine ring is a chair with the N-substituent equatorial. There is evidence of significantly greater torsional angles around the N and O atoms than around the ring C atoms, showing the ring to be more puckered than cyclohexane. The hydrogen bond is between the acid group on one molecule and the ring nitrogen on its neighbour.     

Preparation of isomeric 1,3- and 1,5- (o-phenylene)-hexamethylcyclotetrasiloxanes and investigation of their spectral characteristics

Workup of the mixture of products of pyrolysis of cyclotetrasiloxane (Me₂SiO)₂(MePhSiO)₂ yielded 1,3- (I) and 1,5-(o-phenylene)cyclosiloxane (II), the structures of which were established on the basis of data from their IR, PMR, and mass spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 24–25, January, 1978.     

Analyse systemati oue d'elements en traces dans l'or metalli oue par activation neutroni oue

Résumé Une méthode d'analyse des impuretés dans l'or métallique par activation neutronique, a été mise au point. Après irradiation de 15 heures dans un flux de 2·10¹⁴ n·cm⁻²·sec⁻¹, l'échantillon d'or est traité en cellule blindée. La matrice est séparée des impuretés à analyser par des méthodes électrolytiques. Les impuretés sont généralement séparées en 3 fractions qui sont mesurées par spectrométrie γ. Le traitement des informations est effectué sur ordinateur IBM 360/91 moyennant un programme écrit au laboratoire. 29 éléments sont détectables par cette méthode.     

The determination of lead and nickel by atomic-absorption spectrometry with a flameless wire loop atomizer

In an extension of studies of flameless atomizers for atomic-absorption spectrometry, an electrically heated tungsten-rhenium alloy wire loop was examined. Reduction of metallic salts to ground-state metal atoms was accomplished with the high temperature produced by the loop. Lead and nickel were investigated. Experimental parameters such as wavelength, slit width, atomization temperature and sheathing gas flow rate were optimized. Absolute detection limits of 6.6·10^?10 and 1.2·10^?10, and absolute sensitivities of 7·10^?10 and 8·10^?11 g of lead, were established for unenclosed and enclosed cells, respectively. The interferences of twenty cations and sixteen anions were studied; foreign cations generally enhanced the lead absorption by retarding its vaporization, allowing the slow detection system to respond more efficiently. Nickel was investigated as a representative less volatile metal; an absolute detection limit of 1.6·10^?9 and an absolute sensitivity of 9·10^?10 g of nickel were established.     

Isoperthiocyanic acid (3-amino-5-thione-l, 2, 4-dithiazole) as a new reagent for the selective detection of nitrite ion

Summary A new, simple, and selective test is described for the detection of nitrite ion with isoperthiocyanic acid (I) as the reagent. The test is based on the reaction of a 5% solution ofI with the nitrite ion solution, a deep orange precipitate being formed. Conversely, the test can be used in the identification ofI itself. Presumably, the coloured product is 3-hydroxy-5-thione-1, 2, 4-dithiazole, formed by the action of nitrous acid (producedin situ by the action of sulphuric acid and nitrite) on the 3-amino group ofI. The limit of detection is 300g of NO₂ ^– in a drop (0.05 ml). Most anions (including IO₃ ^–) do not interfere. Only I^–, thiourea, and hydrogen peroxide interfere; S₂O₃ ^2– interferes only when present in large amounts.

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Zusammenfassung Ein neuer, einfacher und selektiver Nachweis von Nitrit mit Isoperthio cyansäure (I) wurde beschrieben. Er beruht auf der Umsetzung einer 5% igen Lösung von I mit Nitritlösung, wobei ein tief orange gefärbter Niederschlag entsteht. Umgekehrt kann die Reaktion auch zum Nachweis von I dienen. Vermutlich handelt es sich bei dem gefarbten Produkt um 3-Hydroxy-5-thion-1, 2, 4-dithiazol, das durch Einwirkung der salpetrigen Säure auf die 3-Aminogruppe von I entsteht. Die Erfassungsgrenze betragt 300g NO₂ ^–im Tropfen (0,05 ml). Die meisten Anionen (inklusive JO₃ ^–) stören nicht. Nur J^–, Thioharnstoff und H₂O₂ stören; Thiosulfat stört nur in großen Mengen.