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51.
Kuśtrowski P Chmielarz L Dziembaj R Cool P Vansant EF 《The journal of physical chemistry. A》2005,109(2):330-336
The novel mesoporous templated silicas (MCM-48, SBA-15, MCF, and MSU) were used as supports for transition metal (Cu, Cr, or Fe) oxides. The catalysts were synthesized using the incipient wetness impregnation, and characterized by low-temperature N2 sorption, DRIFT, photoacoustic IR spectroscopy, UV-vis diffuse reflectance spectroscopy, and temperature-programmed desorption of ammonia. It was shown that the preparation method used results in different distributions and dimensions of the transition metal oxide clusters on the inert support surface. The prepared catalysts were tested in the reaction of oxidative dehydrogenation of ethylbenzene in the presence of nitrous oxide. The iron-containing catalysts showed the highest catalytic activity. The presence of isolated Fe3+ was found to be the most important factor influencing the ethylbenzene conversion. The undesirable effect of the increase in selectivity toward CO2 was observed for the samples with the highest concentrations of acidic surface sites. 相似文献
52.
The paper presents a new method for the generation of acetaldehyde in the amounts that allow to calibrate the measuring system. The method is based on thermal decomposition of surface compounds at the range 130-190 °C, in which an acetaldehyde as the decomposition product is released. The synthetic pathway leading to the desired surface compounds is described. Investigations demonstrated that the synthesis of the compounds on the surface of the support material (silica gel) was carried out homogeneously. The technique proposed was used for the generation of gaseous standard mixtures containing acetaldehyde for the calibration of a thermal desorber-gas chromatograph-flame ionization detector system. 相似文献
53.
The enantioselective addition of allylstannanes and allylsilanes to alkyl glyoxylates of type 1, catalyzed by chiral (salen)Cr(III) complexes 3, has been studied. We have found that the reaction proceeded smoothly for low loading (1-2 mol %) of (1R,2R)-(salen)Cr(III)BF43a or (1R,2R)-(salen)Cr(III)ClO43c, and allyltributyltin under simple, undemanding conditions, affording (R)-2-hydroxypent-4-enoic acid esters 2 in good yield (61-90%) and enantioselectivity (58-76% ee). 相似文献
54.
The synthesis of a novel class of functionalized benzophanes in which a (2′-hydroxy)ethoxy pendant arm is attached to the phenyl ring is reported. The reported approach, utilizes simple starting materials, and skillful organization of the synthetic steps allows for simultaneous transforms of the macrocyclic ring and the pendant arm. Binding studies of these systems with Pd2+ and Cd2+ cations is described. A chromatographic stationary phase containing the benzodiazacoronand moiety was also synthesized, and found to interact specifically with isomeric nitrobenzene derivatives. 相似文献
55.
In this paper we describe the stereoselective synthesis of functionalized lactam 7 via two enantiospecific piperidine-forming techniques and its employment in a general synthetic approach to Nuphar alkaloids. Specifically, the formation of piperidine 18 by formal [3 + 3] cycloaddition and stepwise annelation processes is described; the latter technique was found to be significantly more efficient than the Pd-catalyzed TMM addition process. Finally, exploitation of the exocyclic alkene installed in the piperidine-forming reaction in the transformation of 18 to (-)-deoxynupharidine ((-)-2), (-)-castoramine ((-)-3), and (-)-nupharolutine ((-)-4) via intermediate lactam 7 is delineated. 相似文献
56.
Gawroński J Grycz P Kwit M Rychlewska U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(18):4210-4215
The absolute configuration and the conformation of 9,10-trans-disubstituted 9,10-dihydrophenanthrenes, known chiral metabolites of phenanthrene-9,10-oxide, have been determined by circular dichroism. The absolute configuration assignment is based on the sign of the long-wavelength Cotton effect (A-band), which is conformation invariant and originates from benzylic chirality. This provides a new interpretation of the Mislow biphenyl-helicity rule for the case of the 9,10-dihydrophenanthrene chromophore. The sign of the B-band Cotton effect reflects the conformation of the biphenyl chromophore in 9,10-dihydrophenanthrenes. It is shown that the origin of chiroptical properties of 9,10-dihydrophenanthrenes is closely related to those of 5,6-trans-disubstituted 1,3-cyclohexadienes. 相似文献
57.
Chaudhuri RK Freed KF Hose G Piecuch P Kowalski K Włoch M Chattopadhyay S Mukherjee D Rolik Z Szabados A Tóth G Surján PR 《The Journal of chemical physics》2005,122(13):134105
Tests have been made to benchmark and assess the relative accuracies of low-order multireference perturbation theories as compared to coupled cluster (CC) and full configuration interaction (FCI) methods. Test calculations include the ground and some excited states of the Be, H(2), BeH(2), CH(2), and SiH(2) systems. Comparisons with FCI and CC calculations show that in most cases the effective valence shell Hamiltonian (H(v)) method is more accurate than other low-order multireference perturbation theories, although none of the perturbative methods is as accurate as the CC approximations. We also briefly discuss some of the basic differences among the multireference perturbation theories considered in this work. 相似文献
58.
Piotr Bugiel 《Probability Theory and Related Fields》1991,88(4):483-496
Summary For domainsIR
d
(bounded or not) the notion of a Markov map fromI into itself is developed. It is shown that under a condition of Rényi type and the assumption that the map is Markov, any probability density tends inL
1-norm to a unique invariant measure under the action of the Perron-Frobenius operatorP
. The smoothness and ergodic properties of that invariant measure are studied. The paper generalizes results of Lasota and Yorke from dimension one to higher dimension. 相似文献
59.
The effect of nonradiative reverse energy transport (NRET) in two donor-acceptor systems was studied experimentally. It was found that the NRET occurring in system I; rhodamine 6G (donor) and rhodamine B (acceptor), considerably lowers the emission anisotropy at medium and high concentrations. These results qualitatively confirm the predictions of the approximate theoretical approach of L. Kulak and C. Bojarski (see the preceding paper). In system II; rhodamine 6G (donor) and Nile Blue (acceptor), for which the NRET process does not occur, a good agreement with no-back-transport theory was obtained. 相似文献
60.
Piotr Bugiel 《Monatshefte für Mathematik》1992,113(4):255-263
A class of uniformly expanding, piecewiseC
2-diffeomorphisms from domainsIR
d
(bounded or not) into themselves is considered. It is shown that the number of the extreme points of Fix (P
)={gG:Pg=g} whereP
is the Frobenius-Perron operator associated with andG={gL
1: g0 g=1}, can be determined in an effective way. Moreover, it is shown that the sequence {P
j
g} is convergent inL
1 for anygG, and in the topology of uniform convergence for anygG(1). The limit is a linear projectionR inL
1 (defined by (3.1)) which mapsG onto Fix (P
) (see Th. 3.1).Dedicated to professor A. Lasota on the occasion of his 60th birthday 相似文献