Massenspektroskopische Fragmentierungsreaktionen. V—Zur Frage des Quasi–Thermischen RDA–Zerfalls

It is demonstrated with variously substituted steroids that it is not necessary to invoke quasithermal RDA decomposition to explain the fragmentation behaviour. The results suggest that such processes do not play an important role in mass spectrometric decomposition.     

In situ soft X-ray studies of ethylene oxidation mechanisms and intermediates on the Pt(111) surface

In situ studies of ethylene oxidation on Pt(111) have been performed using a powerful combination of fluorescence yield soft X-ray methods for temperatures up to 600 K and oxygen pressures up to 0.01 Torr. Absolute carbon coverages have been determined both in steady-state and dynamic catalytic conditions on the Pt(111) surface. Fluorescence yield near-edge spectroscopy (FYNES) and temperature-programmed fluorescence yield near-edge spectroscopy (TP-FYNES) experiments above the carbon K edge were used to identify the structure and bonding of the dominant surface species during oxidation. TP-FYNES experiments of preadsorbed ethylene coverages in oxygen pressures up to 0.01 Torr indicate a stable intermediate is formed over the 215-300 K temperature range. By comparing the intensity of the C-H sigma resonance at the magic angle with the intensity in the carbon continuum, the stoichiometry of this intermediate has been determined explicitly. Based on calibration with known C-H stoichiometries, the intermediate has a C(2)H(3) stoichiometry for oxygen pressures up to 0.01 Torr, indicating oxydehydrogenation occurs before skeletal oxidation. FYNES spectra at normal and glancing incidences were performed to characterize the structure and bonding of this intermediate. Using FYNES spectra of ethylene, ethylidyne, and acetylene as reference standard, this procedure indicates the oxidation intermediate is tri-sigma vinyl. Thus, oxidation of ethylene proceeds through a vinyl intermediate, with oxydehydrogenation preceding skeletal oxidation.     

Some Specific Features of Conjugate Addition Reactions with Lithium and Magnesium o-Carborane Derivatives

Reactions of lithium and magnesium o-carborane derivatives with ethyl -nitrocinnamate, ethyl -(3-indolyl)--nitroacrylate, and diethyl m-nitrobenzylidenemalonate were studied. Some specific features of these reactions were established, and preparative methods for the synthesis of previously unknown o-carborane derivatives were developed.     

The effect of preparation procedure and composition of water-ethanol suspensions of amorphous silica on their aggregative stability and kinetics of coagulation

The method of flow ultramicroscopy is employed to study the effect of the composition and preparation procedure of dilute water-ethanol suspensions of two samples of amorphous silica (fractionated fused quartz and monodisperse amorphous silica) on the kinetics of their coagulation. It is revealed that all suspensions prepared by the addition of silica powders to water-ethanol mixtures with ethanol contents of 96 and 40 vol % are stable with respect to aggregation, as the suspensions prepared by the addition of aliquots of concentrated dispersions of the aforementioned silica samples in 96% ethanol aged for different time periods to water-ethanol mixtures containing 96 vol % ethanol. At a 40-vol % content of ethanol in the mixture, the coagulation whose character (including “superfast” coagulation) substantially depends on the time of aging of initial concentrated silica dispersions occurs. Furthermore, kinetic studies are performed for the coagulation of dilute silica suspensions prepared by the addition of silica powders to water-ethanol solutions containing 40 vol % of ethanol and traces (<1 ppm) of poly(ethoxysilane), poly(acrylic acid), and a supernatant prepared by the centrifugation of concentrated silica dispersion in 96% ethanol aged for more than 3 months. It is found that the addition of aliquots of the aforementioned ethanol solutions to silica suspensions in 40% ethanol, which are initially stable with respect to aggregation, causes their superfast coagulation.     

Solution structure of (+)-discodermolide

[structure: see text]. The solution structure of (+)-discodermolide (1) has been determined via 1- and 2-D NMR techniques in conjunction with Monte Carlo conformational analysis. Taken together, the results demonstrate that in solution (+)-discodermolide occupies a helical conformation remarkably similar to the solid state conformation.     

A photoplate calibration technique applied to the determination of hafnium in zirconium by SSMS

A photoplate calibration procedure is suggested for spark source mass spectrometry /SSMS/ with photoplate detection. The technique uses the Churchill two-line method applied to the two stable isotopes of copper. The calibration curve thus obtained is split into fragments and each fragment is approximated by a polynomial. The method was applied for the quantitative determination of Hf as impurity in zirconium sponge obtained from a pilot plant dedicated to the depletion of the hafnium content in zirconium by fractional crystallization.     

Nivyaside — A new glycoside fromLeucanthemum vulgare

From the ligulate flowers ofLeucanthemum vulgare Lam. growing on the territory of the Georgian SSR a new glycoside has been isolated which has been called nivyaside and has the structure 8-(1-α-D-glucopyranosyl-5-deoxyquercit-5-yl)-4′,5,7-trihydroxyflavone.     

The determination of molybdenum and tungsten by high resolution spectrometry of alpha-induced prompt photon emission

A simple, rapid and non-destructive method is described for determining molybdenum and tungsten in steels over the concentration range 0.07 to about 20% by mass. The method uses high resolution spectrometry of the low energy gamma-rays induced by 5 MeV alpha-particle beams. The precision for molybdenum is 2.7% and for tungsten is 0.55% using respectively the 204 and 100.1 keV gamma-rays. Results obtained by Ge(Li) and intrinsic germanium detectors are compared. The extent of interference from other elements is discussed.     

The Effect of Surface Forces on the Thermal Slip of a Simple Gas

The flow of a simple gas along a plane surface under the action of tangential temperature gradient is considered. The velocity of thermal slip is calculated by the variational method with account of the effect of surface forces. It is shown that, in some situations, surface forces can substantially affect the value of the thermal slip coefficient.