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Functionally substituted acrylates 8a,b obtained by direct lithiation of the corresponding acids, and cyclohexanone derivative 6 accessible in a five step sequence afforded spirotetronates 9a,b containing the carbon skeleton and the stereochemistry of the top half of chlorothricolide 1 (R = H). Subsequent direct lithiation of the tetronate moiety in a-position enabled the introduction of the required a-hydroxy group. 相似文献
976.
Rolf Weiel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):89-92
The paper describes the results obtained by an approach to simulating the time evolution of cluster fusion. Further calculations and measurements suggested by these results are also discussed. 相似文献
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Michael Reinke John Mantzaras Rolf Schaeren Rolf Bombach Andreas Inauen Sabine Schenker 《Proceedings of the Combustion Institute》2005,30(2):2519-2527
The homogeneous ignition of CH4/air, CH4/O2/H2O/N2, and CH4/O2/CO2/N2 mixtures over platinum was investigated experimentally and numerically at pressures 4 bar p 16 bar, temperatures 1120 K T 1420 K, and fuel-to-oxygen equivalence ratios 0.30 0.40. Experiments have been performed in an optically accessible catalytic channel-flow reactor and included planar laser induced fluorescence (LIF) of the OH radical for the determination of homogeneous (gas-phase) ignition and one-dimensional Raman measurements of major species concentrations across the reactor boundary layer for the assessment of the heterogeneous (catalytic) processes preceding homogeneous ignition. Numerical predictions were carried out with a 2D elliptic CFD code that included elementary heterogeneous and homogeneous chemical reaction schemes and detailed transport. The employed heterogeneous reaction scheme accurately captured the catalytic methane conversion upstream of the gaseous combustion zone. Two well-known gas-phase reaction mechanisms were tested for their capacity to reproduce measured homogeneous ignition characteristics. There were substantial differences in the performance of the two schemes, which were ascribed to their ability to correctly capture the p–T– parameter range of the self-inhibited ignition behavior of methane. Comparisons between measured and predicted homogeneous ignition distances have led to the validation of a gaseous reaction scheme at 6 bar p 16 bar, a pressure range of particular interest to gas-turbine catalytically stabilized combustion (CST) applications. The presence of heterogeneously produced water chemically promoted the onset of homogeneous ignition. Experiments and predictions with CH4/O2/H2O/N2 mixtures containing 57% per volume H2O have shown that the validated gaseous scheme was able to capture the chemical impact of water in the induction zone. Experiments with CO2 addition (30% per volume) were in good agreement with the numerical simulations and have indicated that CO2 had only a minor chemical impact on homogeneous ignition. 相似文献