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1.
Peter Karduck Norbert Ammann Hans Günter Esser Jörg Winter 《Fresenius' Journal of Analytical Chemistry》1991,341(5-6):315-319
Summary The first wall of the fusion device TEXTOR at the Forschungszentrum Jülich has been coated in situ with an amorphous hydrogen rich carbon/boron film (a-C/B:H) which reduces plasma impurities caused by the plasma surface interaction. The results of the coating process of the 35 m2 large inner wall surface have been controlled by a recently developed modification of the quantitative electron probe microanalysis, which has been applied to 12 samples from specified positions inside the tokamak. The quantification itself is based on a Monte Carlo simulation of electron trajectories providing very accurate results for X-ray intensities emitted by elements present in the electron bombarded sample. The Monte Carlo results are used in the present work to calibrate the measured X-ray intensities emitted by boron and carbon from the a-C/B:H layers deposited on pure silicon substrates. As a result the total deposited mass of the layer per area unit as well as the composition of the layers (except hydrogen) could be determined very accurately. The relative errors were less than 7%. The limit of detectability were found to be in the range of one monolayer for boron as well as for carbon. 相似文献
2.
Willi Jager Peter Lax Cathleen Synge Morawetz 《Journal of Mathematical Sciences》2004,120(3):1242-1246
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6.
Erich Metzger Roland Aeschimann Martin Egli Gaby Suter Ren Dohner Daniel Ammann Max Dobler Wilhelm Simon 《Helvetica chimica acta》1986,69(8):1821-1828
Lipophilic neutral carriers were synthesized which show Li+/Na+ selectivities of up to ca. 80 in highly lipophilic liquid membranes. The sensor membranes exhibit improved response times and increased lifetimes as compared to systems described earlier. They allow reliable measurements of Li+ in blood serum within the clinical concentration range. A 1:1 Li+/ionophore complex of one representative (N,N,N′,N′-tetracyclohexyl-5,5-dimethyl-3,7-dioxaazelaamide) has been prepared, and its structure was elucidated by X-ray analysis. 相似文献
7.
A. V. Willi 《Helvetica chimica acta》1966,49(5):1725-1728
Second order rate constants are determined for the E2 reactions of 2,2-diphenyl-ethyl benzenesulfonates Ph2CxHCH2O · O2S–C6H4–X with CH3ONa in methyl cellosolve solution (xH = H or D, X = p-CH3O, p-CH3, H or p-NO2). The HAMMETT ? values are of the same order of magnitude as those found in the first order solvolyses of methyl, ethyl or isopropyl benzenesulfonates. The primary deuterium isotope effects kH/kD are 5.27, 5.42 and 6.70 for X = p-CH3O, H and p-NO2. The ? values as well as the increase of kH/kD with introduction of p-NO2 supply evidence for simultaneous CαO and CβH bond cleavages also in the E2 reactions of these compounds. 相似文献
8.
The [2 + 2]-cycloaddition of dichloroketene (prepared in situ from CCl3COCl and Zn(Cu)) with three alkynes 1a–c to form 2,3-dimethyl-( 2a ), 2,3-diethyl-( 2b ) and 3-butyl-4,4-dichlorocyclobut-2-enone ( 2c ) proceeds rapidly in the absence of POCl3. The primary products 2a–c rearrange in situ to the 2,4-dichlorocyclobut-2-enones 3a–c under the influence of ZnCL2 produced during the reaction. ZnCl2 converts both 2a and 3a into a 4:6 equilibrium mixture of the two; this isomerization does not occur with LiCl. The Cl-atoms of both 2a , b and 3a , b and of 2c may reductively be removed with Zn(Cu) in AcOH/pyridine to afford the alkylcyclobutenones 4a-c . Without pyridine, this reduction gives ca. 1:1 mixtures of the double-bond isomers 4 and 5 in low yields. The cyclobutenones 2c and 4c may be deuterated by CD3COOD in the presence of pyridine. D -Atom is introduced into 2c at C(4) and at C(γ), and into 4c at C(2) and C(4). A mechanism for this deuteration is considered, which does not involve a cyclobutadienolate 7 , but rather a cyclobutenolate of type 8 . The reductions of 2 and 3 to 4 might also pass through the same type of intermediate 8 . 相似文献
9.
Alfred V. Willi 《Helvetica chimica acta》1973,56(6):2094-2098
It is suggested that the acid catalyzed hydrolyses of isobutene oxide and propene oxide proceed via rate-determining bimolecular reaction between a carbonium ion and solvent water (A2+ mechanism). The carbonium ion is formed by ring opening of the protonated epoxide, in a relatively fast preceding step. This mechanism is in agreement with all experimental facts known today. There is evidence for a similar mechanism in the acid catalyzed hydrolyses of cyclic acetals. 相似文献
10.
Yutaka Morita Manfred Hesse Hans Schmid Avijit Banerji Julie Banerji Asima Chatterjee Willi E. Oberhnsli 《Helvetica chimica acta》1977,60(4):1419-1434
Alstonia scholaris: The structure of the indole alkaloid nareline Besides the known akuammidine, picralinal, picrinine and pseudoakuammigine a new indole alkaloid called nareline (M=352) was isolated from Alstonia scholaris R. BR. , which belongs to the plant family of Apocynaceae. Its structure 2 was deduced by single crystal X-ray diffraction. 2 represents the absolute configuration. The spectroscopic data of 2 and its derivatives (Scheme 1) as well as their chemical behavior support this structure. In biogenetic sense nareline is related to the bases akuammiline ( 4 ) and picraline ( 5 ) (Scheme 2). In contrast to those the C-atom 5 is exocyclic and represents an aldehyde group which forms together with the oxygen atom of the N (4)-hydroxylamine group a cyclic half acetale. - By oxidation (CrO3/CH3COOH) of 2 the oxindol derivative 19 (oxonareline) is formed which contains a cyclic acetal as a partial structure element (Scheme 4). 相似文献