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71.
The regio- and stereoselectivity of the reactions of carbanions, generated from alkanals, carboxylates of the type XYCHCOOEt (X = EtOOC, CN, Ac; Y = H, Br), or derivatives of 3-methyl-4-phosphono-2-butenoic acid using PTC techniques, with aldehydes of various types (alkanals, ,-enals, cross-conjugated enedials, benzaldehydes,etc.) are reviewed. The factors affecting the outcome of these reactions are discussed. The carbanion analogs, triphenylphosphorus ylides, are shown to attack selectively at one of the aldehyde groups of aromatic dialdehydes. The regularities found for the title reactions were used in the syntheses of some biologically active isoprenoids.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1867–1885, October, 1995. 相似文献
72.
M. Slemrod 《Journal of statistical physics》1996,83(5-6):1067-1108
A discrete-velocity Boltzmann model is introduced. It is based on two principles: (i) clusters of particles move in 3 with seven fixed momenta; (ii) clusters may gain or lose particles according to the rules of Becker-Döring cluster equations. The model provides a kinetic representation of evaporation and condensation. The model is used to obtain macroscopic fluid equations which are valid into the metastable fluid regime,
, where is any positive number, is the inelastic Knudsen number, and
s
is the saturation density. 相似文献
73.
Experimental studies of the coil-to-globule transitions exhibited in better than -solvents by interfacial copolymers ofN-isopropylacrylamide and acrylamide imply that a lower bound for the value of n in then-clusters of poly(N-isopropylacrylamide) (PNIPAM) is 3. The corresponding upper bound is therefore likely to be 5 or 6. Statistical copolymers of PNIPAM containing upwards of 0.75 mole fraction of acrylamide (whose homopolymer does not itself displayn-clustering) exhibited this transition, which disappeared at higher mole fractions of acrylamide. Interfacial homopolymers ofN-ethylacrylamide and its statistical copolymers withN-isopropylacrylamide exhibitedn-clustering at all compositions. 相似文献
74.
Jerzy Jeczalik 《Journal of polymer science. Part A, Polymer chemistry》1993,31(5):1161-1164
The title reaction catalyzed by NaOH in aqueous media was studied. The oligomeric products formed are characterized in terms of their yield, structure, etc. The effects of reaction parameters and media are also discussed. The reaction mechanism is proposed. © 1993 John Wiley & Sons, Inc. 相似文献
75.
N-Methylmorpholinium 4-aryl-5-cyano-2-oxo-2-oxo-1,2,3,4-tetrahydropyridine-6-thiolates were obtained by the condensation of
aromatic aldehydes, cyanothioacetamide, and Meldrum's acid in the presence ofN-methylmorpholine. They were then used in the syntheses of substituted 6-alkylthio-3,4-dihydropyridin-2(1H)-ones and 4,5-dihydrothieno[2,3-b]pyridin-6(7H)-ones.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1852–1856, October, 1997. 相似文献
76.
Kaishuo Yang Ehsan Sadeghi Pouya Libin Liu Dr. Ming Li Dr. Xiaoxian Yang Dr. Neil Robinson Prof. Eric F. May Prof. Michael L. Johns 《Chemphyschem》2022,23(4):e202100794
Understanding the behaviour of short-chain hydrocarbons confined to porous solids informs the targeted extraction of natural resources from geological features, and underpins rational developments in separation, storage and catalytic conversion processes. Herein, we report the application of low-field (12.7 MHz) 1H nuclear magnetic resonance (NMR) relaxation measurements to characterise ethane dynamics within mesoporous silica materials exhibiting mean pore diameters between 6 and 50 nm. Our measurements provide NMR-based adsorption isotherms within the range 25–50 bar and at ambient temperature, incorporating the ethane condensation point (40.7 bar at our experimental temperature of 23.6 °C). The quantitative nature of the acquired data is validated via a direct comparison of NMR-derived excess adsorption capacities with ex situ gravimetric ethane adsorption measurements, which are demonstrated to agree to within 0.2 mmol g−1 of the observed ethane capacity. NMR relaxation time distributions are further demonstrated as a means to decouple interparticle and mesopore dominated adsorption phenomena, with unexpectedly rapid relaxation rates associated with interparticle ethane gas confirmed via a direct comparison with NMR self-diffusion analysis. 相似文献
77.
A. A. Balandina V. A. Mamedov E. A. Khafizova Sh. K. Latypov 《Russian Chemical Bulletin》2006,55(12):2256-2264
The combined use of 2D NMR correlation methods and ab initio chemical shift calculations is efficient and, in some cases, virtually the only way to determine the structures of new organic
compounds. This approach enabled us to establish the structure of the major unusual product of the three-component reaction
of imidazo[1,5-a]quinoxalin-4-one, bis(2-chloroethyl)amine hydrochloride, and potassium carbonate in DMF.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2172–2179, December, 2006.
Dedicated to Professor A. V. Il’yasov on the occasion of his 70th birthday. 相似文献
78.
A one-step pathway has been adopted to fabricate biodegradable polylactide (PLA) hollow spheres by interfacial polymerization
in an oil-in-water emulsion system. The mechanism of sphere formation is suggested with respect to interfacial cross-linking
polymerization and subsequent precipitation of the unreacted PLA macromonomers onto the preformed shells. Their hollow nature
and morphology were verified by transmission electron microscopy and scanning electron microscope characterizations. 相似文献
79.
碱金属沸石上乙醇双分子缩合反应及其机理 总被引:1,自引:0,他引:1
首次发现在碱金属X沸石上乙醇能够发生以正丁醇为主产物的双分子缩合反应,在所研究的催化剂中,含Rb的LiX沸石表现出较高的反应活性和选择性。反应机理的研究表明,反应不经过aldol缩合步骤。在此基础上,对反应机理提出了新建议:在碱性沸石作用下,乙醇的β-位C-H键被活化,双分子脱水导致缩合。碳链的增长按此模式进行。 相似文献
80.
Fluorescence decay and quenching of pyrene labels on copolymers of 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and N,N-dimethylacrylamide were observed in dilute salt-free aqueous solutions as a function of the mole fraction FAMPS of AMPS from 0 to 0.896. Monoexponential decay was found for the samples of FAMPS<0.35 and biexponential decay for the samples of FAMPS>0.35. The fast decay component is 80%, and the averaged lifetime 〈τ〉 and lifetime τ1 of the fast decay is decreased with increasing FAMPS. Quenching efficiency of Cu2+, I−, CH3NO2, and dinitrobenzene to the pyrene label was investigated in the framework of Stern-Volmer plot. With increasing FAMPS the quenching efficiency of Cu2+ is increased while that of I− decreased. For the neutral quenchers, the quenching rate constant kq increases when FAMPS<0.449 then decreases, showing a decline of accessibility to the pyrene label. These results were interpreted consistently with the counterion condensation concept, where condensed counterions caused the polyelectrolyte chains to aggregate. The existence of less-polar “temporal aggregated domain” in highly charged polyelectrolytes appears to lead to the slower decay and lower accessibility of the pyrene labels. 相似文献