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排序方式: 共有239条查询结果,搜索用时 53 毫秒
1.
John D. Spence Miranda L. Lackie Nicola A. Clayton Sergio A. Toscano Michelle A. Farmer Esfir Popova Marilyn M. Olmstead 《Tetrahedron letters》2014
Sonogashira coupling of buta-1,3-diynylbenzene with ((2-iodophenyl)ethynyl)trimethylsilane and 1,2-diiodobenzene led to the novel enetriyne, 1-ethynyl-2-(phenylbuta-1,3-diynyl)benzene, and enetetrayne, 1,2-bis(phenylbuta-1,3-diynyl)benzene, respectively. Solid state structural and thermal analyses are also described. In solution, 1-ethynyl-2-(phenylbuta-1,3-diynyl)benzene was found to undergo thermal Bergman cyclization to afford 2-(phenylethynyl)naphthalene. 相似文献
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A substantial quantity of experimental data on rewetting, much of which has not been previously reported, is analysed using the results of calculations of the two-dimensional conduction processes taking place in the walls of tubes, which have been used to simulate the cladding of nuclear fuel elements. Correlations giving the quenching heat-transfer coefficient and sputtering temperature are proposed as a result of the analysis. These correlations may be combined with the previously reported conduction analysis to predict rewetting rates under a wide range of conditions. The new data include falling film rewetting rates measured for a range of system pressures (1–15 bars), initial wall temperatures (200–650°C), coolant mass flowrates (3–50 g sec?1) and subcoolings (0–90°C). Measurements have also been made of rewetting rates by bottom flooding of both saturated and subcooled water at atmospheric pressure. 相似文献
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F. R. Farmer 《Contemporary Physics》2013,54(3):349-360
The article concentrates mainly on the developing pattern of safety thinking and safety practices which have been brought about by, and in turn have influenced, the growth of modern industrial technology, particularly in the nuclear field. The need to minimize the chance of accidents with serious consequences led to pursuit of safety by siting, by containment and by automatic built-in safety mechanisms; these are discussed. Codes of practice and safety guidelines are becoming linked with more quantitative goals to achieve desired objectives in safety and reliability. This is particularly important in the assessment of major hazards. 相似文献
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[(IPent)PdCl2(morpholine)]: A Readily Activated Precatalyst for Room‐Temperature,Additive‐Free Carbon–Sulfur Coupling 下载免费PDF全文
Jennifer L. Farmer Matthew Pompeo Dr. Alan J. Lough Prof. Michael G. Organ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(48):15790-15798
A series of new, easily activated NHC–PdII precatalysts featuring a trans‐oriented morpholine ligand were prepared and evaluated for activity in carbon‐sulfur cross‐coupling chemistry. [(IPent)PdCl2(morpholine)] (IPent=1,3‐bis(2,6‐di(3‐pentyl)phenyl)imidazol‐2‐ylidene) was identified as the most active precatalyst and was shown to effectively couple a wide variety of deactivated aryl halides with both aryl and alkyl thiols at or near ambient temperature, without the need for additives, external activators, or pre‐activation steps. Mechanistic studies revealed that, in contrast to other common NHC–PdII precatalysts, these complexes are rapidly reduced to the active NHC–Pd0 species at ambient temperature in the presence of KOtBu, thus avoiding the formation of deleterious off‐cycle PdII–thiolate resting states. 相似文献
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The reaction of NO-Fe(TPP) with low pressures of NO gas proceeds through three distinct transformations, the first of which we suggest is the formation of an N--N-coupled, (NO)(2) adduct intermediate. The subsequent formation of NO(NO(2))Fe(TPP), which under these conditions readily loses NO, suggests that it is formed by addition of free NO(2) to the starting nitrosyl. A mechanism is proposed which implies that the addition of a competitive O atom acceptor would lead to catalytic production of N(2)O. In agreement with the proposed mechanism, the formation of N(2)O is decoupled from the formation of the nitrite by using PPh(3) as the competitive acceptor. The mechanism of O atom transfer was examined by cross-labeling experiments, which show that both O atoms in the intermediate are equivalent, even under catalytic conditions. The formation of an intermediate was confirmed by IR spectroscopy of the heterogeneous reaction of an NO-Fe(TPP) film with gaseous NO, in which transient, isotope-sensitive nu(NO) bands are seen prior to NO(NO(2))Fe(TPP) formation. Mixed (14)N/(15)N label experiments demonstrate coupling between the two bound nitrosyls in the transient species. 相似文献
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The chain conformation and molecular packing of isotactic poly(p-fluorostyrene) have been examined using calculations made with semiempirical potential energy functions. Isolated chain conformational energies indicate no difference in conformation for the fluoropolymer from the conformation for isotactic polystyrene. The energy for packing poly(p-fluorostyrene) chains into a crystalline array as 31 or 41 helices was also compared with the energies for packing polystyrene in both of these helical forms. While not being the lowest energy mode of packing for poly(p-fluorostyrene), the packing of 41-helices does yield a local energy minimum. Such packing of 41 helical polystrene chains is considerably less energetically feasible. The results indicate the causes for the experimentally observed difference in the crystalline conformations of the two isotactic polymers as being due to intermolecular influences. 相似文献