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1.
本文对广义风险过程中的渐近方差作了非参数估计,得出并证明了两个定理,为广义风险过程中破产概率的区间估计作了理论准备. 相似文献
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8,8"-Biflavonoidsareantw0rtantclass0fbiflavonoids.Asasystematicresearchofthe8,8"-biflav0noids,wehavepreviouslyreportedthestudyonthereactionof2'-hydroxychaloneswithl2-H2SO4-DMSOsystem.'InthispaPer,thesynthesisof5,5",7,7',-tetTameth0xy-8,8"-biflavonela2,4,4",7,7"-tetramethoxy-8,8"-biflavone1b',4',4",,5,5,',7,7"-hexamethoxy-8,8"-biflav0ne1c4and4,4"-dibenZyl0xy-5,5",7,7"-tetramothoxy-8,8"-biflavoneldisreported.ThesyntheticmethodisshownintheSchemebelow.2-Hydroxyacet0phenonescondensedwithsubsti… 相似文献
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Jackson WG Dickie AJ McKeon JA Spiccia L Brudenell SJ Hockless DC Willis AC 《Inorganic chemistry》2005,44(2):401-409
The bis(pentadentate) ligand tmpdtne binds two Co(II) centers, and the entity is readily oxidized to the dicobalt(III) derivative [Co(2)(tmpdtne)Cl(2)](4+) which has been separated into two isomeric forms. NMR studies establish these as meso and rac isomers arising from the different or same absolute configurations for the asym configuration about each Co(III) center. Each dinuclear ion base hydrolyses to the dihydroxo derivative [Co(2)(tmpdtne)(OH)(2)](4+) with retained asym configurations about each metal ion and also retained rac or meso configurations. The kinetics for the stepwise loss of the two Cl(-) ligands is uniphasic, and data are presented to show that the loss of the first chloride is rate determining and is followed by very rapid intramolecular and loss of the second Cl(-) via a hydroxo-bridged species to yield the observed dihydroxo derivative. Meso and rac forms of the latter have been crystallized. The X-ray crystal structure of the rac-dihydroxo complex is reported, and it establishes the configurations of all the complexes reported. The (1)H NMR spectra for the hydroxo ions show very high field Co-OH resonances (ca. delta-0.5 ppm) not observed previously for such ions, and this result is discussed in the context of published (1)H NMR data for bridged Co-OH-Co species. The base hydrolysis kinetics for the dichloro ions are first order in [OH(-)], and deprotonation at an alpha-CH(2) center (alpha to a pyridyl) is identified as the source of the catalysis, since there is no NH center available for deprotonation on the ligand. These data further support the new pseudoaminate base hydrolysis mechanism first reported in 2003. The values of k(OH) for the second-order base-catalyzed reaction are ca. 4.0 M(-1) s(-1) for both the rac and meso isomers, and these results are discussed in terms of the increased acidities of these 4+ cations compared to their 2+ ion counterparts. 相似文献
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高效液相色谱氮杂冠醚键合固定相的合成及性能研究 总被引:2,自引:0,他引:2
我们曾用γ-氯丙基键合硅胶(CPS),在氢化钠(NaH)作用下合成了3-(氮杂-18-冠-6)丙基键合固定相(BCP)[1].该固定相对碱基、核苷酸、硝基苯酚等有较好的分离选择性,但由于NaH对硅胶基质腐蚀作用较大,导致BCP柱效及渗透性较低.本文采... 相似文献
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2,4,6-三硝基苯酚改性锆铝复合氧化物固定相分离富勒烯的色谱性能研究 总被引:1,自引:0,他引:1
制备了用于分离C60和C70的2,4,6-三硝基苯酚改性锆铝复合氧化物高效液相色谱固定相,考察了流动相中甲苯的含量、柱温及流速对C60和C70分离的影响,同时比较了酸腐蚀前后锆铝复合氧化物基质对分离的影响,结果表明,2,4,6-三硝基苯酚改性酸腐蚀后锆铝复合氧化物填料对富勒烯表现出较强的分离能力,具有作为富勒烯制备分离的潜力。 相似文献
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KANG Yong-Feng LIU Lei YAN Wen-Jin XU Zhao-Qing ZHOU Yi-Feng HAN Zhi-Jian NI Ming DA Chao-Shan WANG Rui 《有机化学》2004,24(Z1):163
Development of new or improved methods for the asymmetric preparation of chiral propargylic alcohols has gained considerable significance during the past years because they are useful building blocks for the synthesis of many biologically active compounds and natural products.[1] A series of chiral tridentate ligands were conveniently synthesized from amino acids with good yields (Scheme 1).[2] A preliminary study of the enantioselective alkynylation of benzaldehyde catalyzed by this chiral tridentate ligand was carried out and up to 83% ee of chiral propargyl alcohols was obtained (Table 1 ). A further investigation of the tridentate ligand is currently underway. 相似文献
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A novel [Co(pentaamine)Cl](2+) complex having all tertiary amine or pyridine donors has been synthesized (pentaamine = 1,4-bis(2'-pyridyl)-7-methyl-1,4,7-triazacyclononane). This asym-[Co(dmpmetacn)Cl](2+) species has been completely characterized through 1D and 2D NMR studies, and through the X-ray structure for the ZnCl(4)(2)(-) salt. Despite the lack of an activating NH center, remarkably its hydrolysis to [Co(pentaamine)OH](2+) is base catalyzed (k(OH) 0.70 M(-)(1) s(-)(1), 25 degrees C, I = 1.0 M, NaCl). Detailed NMR studies reveal that the base catalyzed substitution leads to the exchange of just one deuterium in one of the two -CH(2)- pyridyl arms, that is approximately trans to the leaving group, and this occurs during and not after base hydrolysis. Quenching experiments for the reaction of asym-[Co(dmpmetacn)Cl](2+) and control experiments on H/D exchange for the product asym-[Co(dmpmetacn)OD](2+) in OD(-) show that each act of deprotonation at the acidic methylene leads to loss of Cl(-). This is the first established case of base catalyzed substitution for a complex where the effective site of deprotonation is at a pyridyl group. A pronounced kinetic isotope effect is observed for the species perdeuterated at the pyridyl methylenes (k(H)/k(D) = 5.0), consistent with rate limiting deprotonation which is a rare event in Co(III) substitution chemistry. The activation afforded by the carbanion is discussed in terms of a new process coined the pseudo-aminate mechanism. 相似文献
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