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121.
N-Acyl-2-benzoxazolinones readily form trichlorotitanium enolates that react rapidly with aldehydes to provide crystalline syn-aldol adducts in high yield. The resulting products are simply converted to amides, esters, and thioesters. A simple, economical synthesis of 3-hydroxy-2-methylpentanoate N-propionylcysteamine thioesters based on these findings is presented. 相似文献
122.
We built up star-branched polymers, whose morphology is fully determined by diffusion, with p=1,3,6 and 12 branches with a total of 30,000 monomer units. We investigated their structural properties by calculating the monomer-monomer correlation functions. A detailed finite size scaling analysis of the radius of gyration was also performed to determine the exponent and the corrections to scaling. From these results we calculated the fractal dimension of the branched aggregates and obtained: df=1.222(7), for the linear chain, df=1.2305(8), df=1.247(8) and df=1.261(8) for the three, six and twelve branches polymer, respectively. 相似文献
123.
124.
Measurements were made to decide between two solutions of the title problem. In question was the limiting value of the stress-concentration factor at the edge of a large hole in a tensile strip as the hole diameter approached the strip width. The results indicate that the stress-concentration factor is near two and support one of the solutions with a minor qualification. 相似文献
125.
α-(Phenylthio)alkylboranes, which are easily prepared by two different homologation processes, are deboronated by N-chlorosuccinimide in mildly basic methanol to form monothioacetals or, with excess reagent, dimethyl acetals. Both boronic esters and trialkylboranes react, the latter considerably faster. The reaction is specific for the sulfur-substituted alkylborane group, suggesting that initial chlorination occurs at sulfur. Under free radical conditions, α-(phenylthio)alkaneboronic esters are cleaved to α-(phenylthio)alkyl chlorides by either N-chlorosuccinimide or sulfuryl chloride. Pinacol phenylthio(triphenylstannyl)methaneboronate with sulfuryl chloride yielded (phenylthio)dichloromethane, without any evidence of selectivity between carbontin and carbonboron bond cleavage. 相似文献
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Baragaña B Blackburn AG Breccia P Davis AP de Mendoza J Padrón-Carrillo JM Prados P Riedner J de Vries JG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(13):2931-2936
The cationic steroidal receptors 9 and 11 have been synthesized from cholic acid 3. Receptor 9 extracts N-acetyl-alpha-amino acids from aqueous media into chloroform with enantioselectivities (L:D) of 7-10:1. The lipophilic variant 11 has been employed for the enantioselective transport of N-acetylphenylalanine, a) through dichloromethane (DCM) and dichloroethane (DCE) bulk liquid membranes (U-tube apparatus), and b) through 2.5% (v/v) octanol/hexane via hollow fibre membrane contactors. Significant enantioselectivities and multiple turnovers were observed for both types of apparatus. 相似文献
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130.
M. P. D. Dobay A. Piera Alberola E. R. Mendoza J. O. R?dler 《Journal of nanoparticle research》2012,14(4):1-12
Intermolecular energy decomposition analysis (EDA) is reported for the binding of CO2 with zeolitic imidazole frameworks (ZIF) to provide a molecular level interpretation of the recent capacity and selectivity measurements of several ZIFs and to suggest a theoretical guideline to improve their performance further, using 1?nm size of organic linker fragment of the ZIFs as a target molecule. The EDA suggests that the local electronic interaction of CO2 and the substituent groups, mainly frozen density and polarization interactions with little charge transfer, is the primary binding interaction, but the electron correlation effects can be equally or more important depending on the binding geometry and functional groups. The present correlated calculations identify the preferred ZIF binding sites for various gases including CO2 to be mostly near the benzene substituent groups rather than the plane of imidazole rings. We predict that the NH2-substituted ZIF would have an enhanced capacity of CO2 as compared to the NO2-substituted ZIF that was recently synthesized and reported to be one of the materials with the best capacity results along with high gas selectivity. The present calculations may imply that the local functionality of the linking organics, rather than detailed framework structures, may be of primary importance in designing certain high capacity MOF or ZIF materials. 相似文献