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101.
tBuLi‐Mediated One‐Pot Direct Highly Selective Cross‐Coupling of Two Distinct Aryl Bromides 下载免费PDF全文
Dr. Carlos Vila Sara Cembellín Dr. Valentín Hornillos Massimo Giannerini Dr. Martín Fañanás‐Mastral Prof. Dr. Ben L. Feringa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15520-15524
A Pd‐catalyzed direct cross‐coupling of two distinct aryl bromides mediated by tBuLi is described. The use of [Pd‐PEPPSI‐IPr] or [Pd‐PEPPSI‐IPent] as catalyst allows for the efficient one‐pot synthesis of unsymmetrical biaryls at room temperature. The key for this selective cross‐coupling is the use of an ortho‐substituted bromide that undergoes lithium–halogen exchange preferentially. 相似文献
102.
The kinetics and mechanism of the reaction between nitrous acid and bromine are studied in dilute sulfuric acid medium, using both the stopped‐flow method and conventional spectrophotometry. The partial reaction order with respect to Br2 moderately differs from 1, showing a saturation at a higher concentration of bromine. The second order of the reaction towards nitrous acid has been observed. Hydrogen and bromide ions significantly suppress the rate of reaction. Despite the apparent simplicity, the mechanism is rather complex, with two reaction pathways proposed. The first one is represented by the reaction of bromine with the intermediate dinitrogen trioxide. A direct nucleophilic attack of NO2− ion towards the bromine molecule is suggested as the second pathway. The proposed mechanism accounts for the observed behavior; in almost all cases a satisfactory quantitative agreement with the experiments is obtained. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 279–285, 2000 相似文献
103.
Galliano Valent 《Letters in Mathematical Physics》2014,104(9):1121-1135
Matveev and Shevchishin have constructed a family of superintegrable models, involving a linear and a cubic integral. Their metrics, when defined on a closed manifold, have the remarkable property of being Zoll metrics. Using the explicit form of the metrics defined on \({\mathbb{S}^2}\) , which we obtained in a recent paper, we reduce them to a canonical form which displays their Zoll property. For the same class of models several metrics are defined on Tannery’s orbifold and we show, by the same procedure, that in this case we are led either to Zoll or to Tannery surfaces. 相似文献
104.
Ferreres F Gil-Izquierdo A Valentão P Andrade PB 《Rapid communications in mass spectrometry : RCM》2011,25(22):3441-3446
The metabolite profiling of Gomphrena globosa inflorescences was performed by high-performance liquid chromatography-diode array detection/electrospray ionization multi-stage mass spectrometry (HPLC-DAD/ESI-MS(n)). Based on the fragmentation patterns, 24 phenolic compounds were characterized. The identified phenolics include p-coumaric and ferulic acids, quercetin, kaempferol, isorhamnetin, and hydroxylated 6,7-methylenedioxyflavone derivatives, as well as their aglycones, none of them reported before in the species. This is also the first time that tetrahydroxy-methylenedioxyflavone derivatives and acetylglycosides are described in nature. Betacyanins were also found. This study significantly extends the knowledge of the G. globosa metabolome, by providing further insights into its phenolic composition. 相似文献
105.
Measurements of bubble growth rate, detachment diameter and heat-transfer are reported for nucleate boiling of binary mixtures in various concentrations on a horizontal heating surface. The growth rate, characterized by the Jakob-number exhibits maximum at 30% (mass) ethylalcohol in the liquid phase. At this concentration the smallest heat transfer coefficient was measured. For growth rate this proves an influence of mass transfer across the phase boundary besides hydrodynamic and thermal effects. 相似文献
106.
I. Novák A. Popelka M. Valentín I. Chodák M. Špírková A. Tóth 《International Journal of Polymer Analysis and Characterization》2014,19(1):31-38
Polyamide (PA) 6 was modified by diffuse coplanar surface barrier discharge (DCSBD) plasma in an atmosphere of nitrogen and oxygen. The surface roughness decrease of PA 6 was detected by AFM and nano-indentation after modification in DCSBD plasma. A significant increase in O/C and N/C ratios of plasma-modified PA 6 using XPS analysis was found. The results show the importance of introducing oxygenic polar functional groups on the polymeric surface in order to increase its surface energy during a short time of plasma activation. The modification of PA 6 by DCSBD oxygen plasma was more efficient than by nitrogen plasma. 相似文献
107.
We developed a sensitive and selective method for quantifying nitrate, thiocyanate, perchlorate and iodide in human urine using ion chromatography coupled with electrospray ionization tandem mass spectrometry. Analysis of proficiency testing materials and spiked urine indicates that the method is precise (coefficients of variation <5%) and accurate (relative percent differences <7.9%). Analytical response was linear across the physiologically relevant concentration range for the analytes, and adequately sensitive to quantify the analytes in >99% of urine samples tested. Measurement of these four toxicologically-related analytes in one assay will provide useful information for assessing potential linkage between exposure and health effects. 相似文献
108.
Meirinhos J Silva BM Valentão P Seabra RM Pereira JA Dias A Andrade PB Ferreres F 《Natural product research》2005,19(2):189-195
Twenty three samples of 18 Portuguese olive leaf cultivars were analysed by a reversed-phase HPLC/DAD procedure and eight flavonoidic compounds were identified and quantified (luteolin 7,4'-O-diglucoside, luteolin 7-O-glucoside, rutin, apigenin 7-O-rutinoside, luteolin 4'-O-glucoside, luteolin, apigenin and diosmetin). Luteolin 7,4'-O-diglucoside and luteolin 4'-O-glucoside were identified by HPLC/DAD/MS/MS - ESI. The studied olive leaf samples showed a common phenolic pattern, in which luteolin 4'-O-glucoside was almost always the major compound. 相似文献
109.
Valentí R Saha-Dasgupta T Alvarez JV Pozgajcic K Gros C 《Physical review letters》2001,86(23):5381-5384
We determine the electronic structure of the one-dimensional spin- 1 / 2 Heisenberg compound gamma-LiV2O5, which has two inequivalent vanadium ions, V(1) and V(2), via density-functional calculations. We find a relative V(1)-V(2) charge ordering of roughly 70:30. We discuss the influence of the charge ordering on the electronic structure and the magnetic behavior. We give estimates of the basic hopping matrix elements and compare with the most studied (alpha)'-NaV2O5. 相似文献
110.
An isocoumarin was isolated from the aerial parts of Centauriwn erythraea Rafn. (Gentianaceae). Its structure was established by spectroscopic means as 5-formyl-2,3-dihydroisocoumarin. 相似文献