The course of the reaction of alkalide K−, K+(15-crown-5)21 with selected alcohols depends on the kind of alcohol and the mode of substrate delivery. In the case of methanol, potassium methoxide formed initially undergoes destruction at the excess of 1. It results in potassium oxide and methylpotassium. The latter opens the crown ether ring giving potassium tetraethylene glycoxide vinyl ether and methane. A similar course of the process is observed for propanol. Potassium glycidoxide is the main product formed in the reaction of 1 with glycidol. Its oxirane ring is opened at the excess of 1. Organopotassium alkoxides, i.e., potassium potassiomethoxide and dipotassium potassiopropane-1,2-dioxide are intermediate products of this reaction. They react then with the crown ether. Potassium methoxide, potassium enolate of acetaldehyde, dipotassium propane-1,2-dioxide and potassium tetraethylene glycoxide vinyl ether are the final products of this process. 相似文献
Although , (Fp η-C5H5Fe(CO)2) (I) is stable and characterizable, the lower homologue FpCH2CH(CO2CH3)2 (II) is not; this we attribute to a facile elimination reaction resulting from the relatively acidic β-hydrogen of II. Formation of I from Fp? and XCH2CE2CH3 (X Br, Cl; E CO2CH2CH3) and cleavage of its FeC bonds (using H+, Br2, CeIV and HgII) occur without major amounts of ester group migrations, even though ·CH2CE2CH3 radicals are involved in some of these reactions. 相似文献
This paper is dedicated to the problem of optimizing the transmission properties of a Pulse Amplitude Modulation (PAM) system. The system is disturbed by a random timing jitter in the sampling device which periodically evaluates the continuous output signal at discrete times. Mathematically the timing jitter is a random variable with unknown probability distribution. So, our optimization problem turns out to be actually a minimax problem, for which mathematical game theory with its powerful concepts becomes the suitable frame for our analysis.In the first part [4] we have established a general existence theorem for the minimax problem, and we have worked out some properties of solutions in the case that the feasible impulse responses form a space of infinite dimension.This part summarizes results which we obtain, if we allow only for impulse responses lying in a certainn-dimensional subspace of the original space (see [2, 3]). By general results from semi-infinite optimization (see [1]) we know that, writing the minimax problem as a semi-infinite optimization problem, we can reduce the number of restrictions from infinity to a numbersn+1. On the basis of our special model we present a theory of uniformly singular quadratic forms, which has been developed (see [3]) in order to get additional statements abouts.In this way we supplement the work of Krabs [6], who was the first to present such a finite dimensional model, arguing that it is impossible for an engineer to construct a system in a way that an arbitrary impulse response is realized, unless this impulse response has a simple structure (for instance a low pass filter).The first two paragraphs have been taken almost literally from part I in order to render the lecture more comfortable. The interesting parts, however, are the following ones, where the results specific for the finite dimensional case are worked out. 相似文献
Three new psychollatine-derived monoterpene indole alkaloids were obtained from Psychotria umbellata Thonn.: 3,4-Dehydro-18,19-β-epoxy-psychollatine (2), N4-[1-((R)-2-hydroxypropyl)]-psychollatine (3), and N4-[1-((S)-2-hydroxypropyl)]-psychollatine (4). Their structures were determined by 1H and 13C NMR spectra, 2D correlations (COSY, HMQC, and HMBC), and mass and UV spectra. Compounds 3 and 4 were synthesized for structural confirmation and for the determination of the stereochemistry of the hydroxyl group. 相似文献
Aluminum pigments were coated with Fe2O3 and CuO by solution-based thermal decomposition of the urea nitrate compounds hexakisureairon(III)nitrate and tetrakisureacopper(II)nitrate. The deposition process was optimized to obtain homogeneously coated aluminum pigments. The growth of the surface coatings was controlled by investigation with scanning electron microscopy, energy dispersive X-ray spectroscopy and static light scattering as well as infrared, X-ray diffraction and thermogravimetric analysis. The iron precursor showed an incomplete decomposition in solution, incorporating traces of urea molecules inside the coatings while the copper precursor showed complete dissociation accompanied by in situ formation of amine complexes. The amount of organic residues resulting from ligand fragments in the final oxide coatings could be reduced to 22 % for the iron oxide and 12 % for the copper oxide by further temperature treatment in solution (259 °C). Colorimetric investigations of the obtained pigments revealed an excellent hiding power, outperforming the pigments used in current state-of-the-art formulations. 相似文献