排序方式: 共有34条查询结果,搜索用时 15 毫秒
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Abil E. Aliev Alex J. Sinclair Shen Zhou John D. Wilden Stephen Caddick Dimitri M. Kullmann Dmitri A. Rusakov 《Journal of Physical Organic Chemistry》2009,22(6):607-612
While developing a synthesis towards tagged dizocilpine (MK‐801) analogues, we observed highly restricted inversion of a nitrogen centre in a number hydroxylamines obtained as key intermediates. These compounds are shown to possess some of the structural elements which are expected to significantly hinder the nitrogen inversion, potentially leading to hydroxylamines with a chiral nitrogen centre. Free energy barriers (ΔG≠) of the nitrogen inversion were estimated to be ca. 22 kcal mol?1 at temperatures near 420 K using variable temperature NMR measurements in DMSO‐d6. Further density functional studies of a number model systems were undertaken in order to better rationalize the measured inversion barriers and follow the role of various structural factors in raising the barrier height of the nitrogen inversion process. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Johannes Wilden 《Applied Surface Science》2007,254(4):1067-1072
The free-form net shape laser synthesis of nanostructured ceramics from liquid precursors enables a residual stress-free production of high temperature resistant ceramic units and components for the use in microsystem engineering. Due to the use of molecular compounded liquid, ceramic precursors the resulting ceramic components show outstanding properties, for example high purity and a nanostructured material design.The use of pulsed lasers enables a defined input of energy required to pyrolyse the precursor material into a crystalline ceramic, so the active volume can be reduced significantly compared to other processes, for example pyrolysis by furnace.In this paper several methods for a further minimization of the active volume are presented. The investigations determined different factors affecting the process. Realizing selective experiments allows a determination of their influencing level and the definition of a working area to produce three-dimensional components with high aspect ratio.By several studies, e.g., scanning electron microscopy, transmission electron microscopy as well as X-ray diffraction analysis, the atomic structure and composition of the created components were analyzed and valued, so the different reaction processes can be described extensively. 相似文献
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We report here, a method of accelerating the rate of aminolysis of PFP sulfonates to yield sulfonamides using tetrabutylammonium salts. We have previously explored the utility of employing PFP sulfonates in the formation of sulfonamides; however we demonstrate here the advantages of combining the existing methodology with a revised protocol which allows the diversity within both the sulfonate ester and the amine to be extended. 相似文献
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Timothy Astley Gordon G. Birch Michael G. B. Drew P. Mark Rodger Gareth R. H. Wilden 《Journal of computational chemistry》1998,19(3):363-367
The traditional method of analyzing solution structuring properties of solutes using atom–atom radial distribution functions (rdfs) can give rise to misleading interpretations when the volume occupied by the solute is ignored. It is shown by using the examples of O(4) in α- and β-D-allose that a more reliable interpretation of rdfs can be obtained by normalising the rdf using the available volume, rather than the traditional volume of a spherical shell. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 363–367, 1998 相似文献
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A synthesis of indoles based on a vinyl sulfonate template is described. The approach employs a sulfonate group which plays three discrete roles in the synthetic sequence. Firstly the highly electron-withdrawing sulfonate group behaves as an activating group for a 1,4-addition of an aniline to the unsaturated system. Secondly, the electron-withdrawing nature of the same group also allows it to behave as a radical stabilising group which facilitates radical cyclisation to an aromatic ring to yield a transient indoline. Finally, the pendant sulfonate group behaves as a leaving group to yield the indole. 相似文献
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Klaß Larissa Ritz Philipp Hirsch Marius Kettler John Havenith Andreas Wilden Andreas Modolo Giuseppe 《Journal of Radioanalytical and Nuclear Chemistry》2021,329(2):565-580
Journal of Radioanalytical and Nuclear Chemistry - Radioactive mercury waste constitutes a significant challenge, as no approved disposal concept yet exists for such waste in Germany. This work... 相似文献
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J. K. Brooks Kazuyuki Saitô JD Maitland Wright 《Rendiconti del Circolo Matematico di Palermo》2003,52(1):5-14
LetA be aC*-algebra with second dualA″. Let (φ
n)(n=1,...) be a sequence in the dual ofA such that limφ
n(a) exists for eacha εA. In general, this does not imply that limφ
n(x) exists for eachx εA″. But if limφ
n(p) exists whenever p is the range projection of a positive self-adjoint element of the unit ball ofA, then it is shown that limφ
n(x) does exist for eachx inA″. This is a non-commutative generalisation of a celebrated theorem of Dieudonné. A new proof of Dieudonné’s theorem, for
positive measures, is given here. The proof of the main result makes use of Dieudonné’s original theorem. 相似文献