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排序方式: 共有882条查询结果,搜索用时 15 毫秒
831.
Nicolaas P. van Leest Lars Grooten Dr. Jarl Ivar van der Vlugt Prof. Dr. Bas de Bruin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(23):5987-5993
A new method for the one-step C−H amination of xanthene and thioxanthene with sulfonamides is reported, without the need for any metal catalyst. A benzoquinone was employed as a hydride (or two-electron and one-proton) acceptor. Moreover, a previously unknown and uncatalyzed reaction between iminoiodanes and xanthene, thioxanthene and dihydroacridines (9,10-dihydro-9-heteroanthracenes or dihydroheteroanthracenes) is disclosed. The reactions proceed through hydride transfer from the heteroarene substrate to the iminoiodane or benzoquinone, followed by conjugate addition of the sulfonamide to the oxidized heteroaromatic compounds. These findings may have important mechanistic implications for metal-catalyzed C−H amination processes involving nitrene transfer from iminoiodanes to dihydroheteroanthracenes. Due to the weak C−H bond, xanthene is an often-employed substrate in mechanistic studies of C−H amination reactions, which are generally proposed to proceed via metal-catalyzed nitrene insertion, especially for reactions involving nitrene or imido complexes that are less reactive (i.e., less strongly oxidizing). However, these substrates clearly undergo non-catalyzed (proton-coupled) redox coupling with amines, thus providing alternative pathways to the widely assumed metal-catalyzed pathways. 相似文献
832.
研究了在酸性镀铜溶液中添加不同分子量的PEG对直径为50微米、深径比为1的镀层盲孔填充效果的影响.结果表明,随着PEG分子量的增加,电镀铜溶液的微孔填充力明显提高.电流密度为2 A/dm2,添加剂PEG分子量(u)超过6000时,镀液可以完全填充盲孔,镀层不出现任何空洞和缝隙.这是由于添加剂PEG能明显加强电镀铜镀液阴极极化,抑制了电镀铜的沉积.同时,PEG于镀液中的扩散系数还随其分子量的增加而降低,从而增加了SPS在微孔底部的吸附力,加速了电镀铜在微孔底部的沉积.进一步,增大PEG分子量,沉积铜膜的表面粗糙度、铜膜结晶度和电阻率均有所降低. 相似文献
833.
Violations of Bell inequality, Cauchy-Schwarz inequality and entanglement in a two-mode three-level atomic system are investigated. It is shown that there are some states, which are entangled but do not violate Bell inequality in this system. Moreover, the relations of violations of Bell inequality, Cauchy-Schwarz inequality, and entanglement are discussed in detail. 相似文献
834.
835.
A calculation of the A = 14 levels is performed by using the weak coupling approach. Very good agreement with experiment is obtained as all known levels below 13 MeV in 14N are satisfactorily explained. A few additional states are predicted to be found. The electromagnetic transition strengths are calculated and reproduce the experimental values in almost all cases. In particular, a simple calculation of the isospin mixture of the negative-parity states provides an explanation of the known T-forbidden E1 transitions. Also the reduced proton widths are considered and are found to be consistent with (p, p) scattering experiments on 13C. 相似文献
836.
837.
Recent experiments indicate a connection between the low- and high-frequency noises affecting superconducting quantum systems. We explore the possibilities that both noises can be produced by one ensemble of microscopic modes, made up, e.g., by sufficiently coherent two-level systems (TLS's). This implies a relation between the noise power in different frequency domains, which depends on the distribution of the parameters of the TLS's. We show that a distribution, natural for tunneling TLS's, with a log-uniform distribution in the tunnel splitting and linear distribution in the bias, accounts for experimental observations. 相似文献
838.
839.
一类具不变性质的变系数偏微分方程的特解 总被引:1,自引:0,他引:1
In this paper, a few properties of general patial differential operator P beinginvariant with respect to the form F(|x|pp+|y|qq-|z|rr) are studied, where x∈Rn,y∈ Rm, z∈Rl.and explicit formulas are given for certain solution of the equation Pu=Aδ with P being a differential operator with power function coefficientswhich preserves the form (|x|pp+|y|qq-|z|rr)1/v for arbitrary even integers p, q, r,and odd integers v. 相似文献