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101.
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Selective formation - in intramolecular Wittig condensations - of the 2-oxocephem-4-carboxylate 8a and of the 2-acetylpenem-3-carboxylate 9 , respectively, was observed as a consequence of different carbonyl reactivities in two homologous α-oxoacylthio groupings. Free, racemic and 7-unsubstituted 2-oxocephem-4-carboxylic acid ( 10 ) was prepared from 8a for biological testing. Attempts to prepare the free 2-acetylpenem-3-carboxylic acid from 9 failed, probably due to the high lability of the β-lactam system. 相似文献
104.
Warren J. Grigsby Lyndsay Main Brian K. Nicholson 《Journal of organometallic chemistry》1997,540(1-2):185-187
Orthomanganated aryl ketones undergo NiBr2(PPh3)2-promoted reactions with activated alkenes to give indanol products with higher specificity than similar Pd(II)- or Me3NO-promoted reactions. 相似文献
105.
Kunikeev SD Atilgan E Taylor HS Kaledin AL Main J 《The Journal of chemical physics》2004,120(14):6478-6486
A singular value decomposition based harmonic inversion signal processing scheme is applied to the semiclassical initial value representation (IVR) calculation of molecular vibrational states. Relative to usual IVR procedure of Fourier analysis of a signal made from the Monte Carlo evaluation of the phase space integral in which many trajectories are needed, the new procedure obtains acceptable results with many fewer trajectories. Calculations are carried out for vibrational energy levels of H2O to illustrate the overall procedure. 相似文献
106.
Metal ions were determined chromatographically as their metal chelates after complexation with 2,6-diacetylpyridine bis(N-methylenepyridiniohydrazone). At a pH of 7 it was possible to separate and determine eight metal complexes, in a single run, under gradient conditions on a polyestyrene-divinylbenzene polymer-based column. Possible separation of rare earth complexes and ion-pairing behavior were also investigated. Linear calibration ranges and detection limits are presented for the metal complexes of Sn(II), Ti(IV), Mn(II), Co(II), Cd(II), Sb(III), Cu(II), Ni(II) and U(VI). Interferences due to the presence of other metal ions in solution were also investigated. 相似文献
107.
The evolution of sulphur dioxide and carbon dioxide during the reaction between concentrated sulphuric acid and low density polyethylene, isotactic polypropylene and atactic polypropylene at 100–125°C has been followed. Atactic polypropylene is the most susceptible, and isotactic the least susceptible, to acid attack, and this order of reactivity can be accounted for by both structural and morphological effects. It appears that acid attack is partially autocatalytic in nature. 相似文献
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109.
Thermal reaction of [H3Mn3(CO)12] with Ph2PC6H4NH2-2 gives good yields of [Mn2(CO)6(PPh2C6H4NH)2], an X-ray single crystal structure determination of which reveals a P,N-chelating ligand with each of the NH groups, formed by deprotonation of the amine groups, bridging the two metal atoms. 相似文献
110.
Hydrogenation of carbon dioxide catalyzed by ruthenium trimethylphosphine complexes: the accelerating effect of certain alcohols and amines 总被引:1,自引:0,他引:1
Munshi P Main AD Linehan JC Tai CC Jessop PG 《Journal of the American Chemical Society》2002,124(27):7963-7971
A trace amount of alcohol cocatalyst and a stoichiometric amount of base are required during the hydrogenation of CO(2) to formic acid catalyzed by ruthenium trimethylphosphine complexes. Variation of the choice of alcohol and base causes wide variation in the rate of reaction. Acidic, nonbulky alcohols and triflic acid increase the rate of hydrogenation an order of magnitude above that which can be obtained with traditionally used methanol or water. Similarly, use of DBU rather than NEt(3) increases the rate of reaction by an order of magnitude. Turnover frequencies up to 95,000 h(-1) have now been obtained, and even higher rates should be possible using the cocatalyst and amine combinations identified herein. Preliminary in situ NMR spectroscopic observations are described, and the possible roles of the alcohol and base are discussed. 相似文献