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This work presents the transportation of Li+ ions at the interface of a charging LiCoO2 electrode through the substrate-generation/tip-collection (SG/TC) feedback mode of scanning electrochemical microscopy (SECM).
The TC current, due to the reduction of the ethylene carbonate (EC) supermolecule, is collected more strongly at 1.8 V than
that of the Li+(DEC)
n
at 2.5 V near at the substrate because of the increased concentration of the supermolecule Li+(EC)m, which means that the electrolyte is not uniformly distributed over the substrate. The smooth SG/TC current loop is formed
at the probe position optimized by the probe scan curve technique between the LiCoO2 substrate with 4.0 V and the probe with 1.8 V, which is applied to analyze the Li+ ion transport at the interface of the LiCoO2 electrode. Moreover, the LiCoO2 substrate, which has a flat surface, is imaged to the nonuniform surface electrochemically by the SECM. We infer that these
experimental techniques will help analyze transporting Li+ ions at the interface and the electrochemical uniformity of the electrode. 相似文献
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Lee SJ Terrazas MS Pippel DJ Beak P 《Journal of the American Chemical Society》2003,125(24):7307-7312
An endocyclic restriction test for acid-catalyzed transfer of chlorine from a protonated chloroamine to an aromatic ring provides data that are consistent with a transition structure with a large bond angle between the entering and leaving groups around chlorine. These results rule out a dissociative mechanism or a mechanism that has an oblique angle between the entering and leaving groups. 相似文献
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Johnson TA Jang DO Slafer BW Curtis MD Beak P 《Journal of the American Chemical Society》2002,124(39):11689-11698
(-)-Sparteine mediated lithiations of N-Boc-allylic and benzylic amines provide configurationally stable intermediates which on conjugate additions to nitroalkenes provide highly enantioenriched enecarbamate products in good yields, and with high diastereoselectivities. Straightforward transformations of these adducts offer general routes to substituted 3,4-substituted piperidines, 3,4-substituted pyrrolidines, and 4,5-substituted pyrimidinones. Diastereoselective substitutions of intermediate lactams followed by reduction provide 3,4,5-substituted piperidines and 3,4-trisubstituted pyrrolidines. Lithiation adjacent to nitrogen of 3,4-substituted piperidines and pyrrolidines followed by diastereoselective substitution opens a route to 2,4,5- and 2,4,5,6-substituted piperidines as well as 2,3,4- and 2,3,4,5-substituted pyrrolidines. The enantiomers of the enecarbamate and 3,4-substituted piperidine products may be accessed by stannylation/transmetalation sequences as well as by further manipulation of 4-substituted piperidones. The methodology is used to synthesize both enantiomers of an aspartic peptidase inhibitor intermediate, 3-hydroxy-4-phenylpiperidine, as well as the antidepressant (+)-femoxetine. 相似文献
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Bailey WF Beak P Kerrick ST Ma S Wiberg KB 《Journal of the American Chemical Society》2002,124(9):1889-1896
The asymmetric deprotonation of N-Boc-piperidine (3) by the 1:1 complex of a sec-alkyllithium and (-)-sparteine has been investigated both experimentally and computationally. The lithiation of 3 with sec-BuL-(-)-sparteine at -78 degrees C, which is a much slower process than is the analogous deprotonation of N-Boc-pyrrolidine (1) and a minor reaction relative to the competing addition of sec-BuLi to the carbamate, proceeds with a moderate degree of selectivity (er = 87:13) for removal of the pro-S hydrogen of 3. The related deprotonation of N-Boc-4-tosyloxypiperidine (6) with two molar equiv of sec-BuL-(-)-sparteine also involves preferential transfer of the pro-S hydrogen. The computational study of the deprotonation of (3) by i-PrL-(-)-sparteine found that the proton that is preferentially transferred within three-component intermediate complex is the thermodynamically least acidic alpha-hydrogen of 3. The asymmetric deprotonation of 3 is calculated to proceed with poor enantioselectivity and to have an activation energy considerably higher than that calculated for deprotonation of N-Boc-pyrrolidine (1). The experimental and computational results are in good agreement. 相似文献
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D J Pippel G A Weisenburger N C Faibish P Beak 《Journal of the American Chemical Society》2001,123(21):4919-4927
The (-)-sparteine-mediated asymmetric lithiation-substitution of (E)-N-Boc-N-(p-methoxyphenyl)-3-cyclohexylallylamine ((E)-5) to afford gamma-substituted enantiomerically enriched products 6 is reported. The solution structure for the lithiated intermediate 8.1 in these reactions was determined by heteronuclear NMR to be a configurationally stable, alpha-lithio, eta(1)-coordinated monomer. This intermediate is proposed to exist as two rotamers that are rapidly equilibrating on the NMR time scale; competitive electrophilic substitution of each conformation results in the formation of Z or E products. Kinetic measurements of the lithiation by in situ infrared spectroscopy provide pseudo-first-order rate constants for reactions with a variety of concentrations of amine, (-)-sparteine, and n-BuLi. The reaction is first order in amine and zero order in 1:1 base--ligand complex. When the concentration of n-BuLi is varied independently of (-)-sparteine concentration, the reaction rate exhibits an inverse dependence on n-BuLi concentration. The deuterium isotope effect for the reaction was determined to be 86 at -75 degrees C, a result consistent with C--H bond breaking in the rate-determining step and indicative of tunneling. A reaction pathway involving a prelithiation complex is supported by kinetic simulations. 相似文献