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991.
Storsberg J Yao ML Ocal N de Meijere A Adam AE Kaufmann DE 《Chemical communications (Cambridge, England)》2005,(45):5665-5666
The first example of a pi,sigma domino-Heck reaction under concomitant rearrangement of the tetracyclic allylcyclopropane endo,exo-bishomobarrelene (5) is reported; the stereoselective reaction proceeds via an intramolecular insertion of a primarily-formed carbopalladation intermediate into a strained cyclopropane C-C sigma-bond, giving 9. 相似文献
992.
Montserrat Barquín María J. Gonzlez Garmendia Liher Larrínaga Elena Pinilla María R. Torres 《无机化学与普通化学杂志》2005,631(11):2210-2214
The complexes of copper formato with pyrazine and dimethylpyrazines: Cu(HCOO)2(pyrz) ( 1 ), Cu2(HCOO)4(pyrz) ( 2 ), Cu2(HCOO)4(2,3‐Me2pyrz) ( 3 ), Cu2(HCOO)4(2,5‐Me2pyrz) ( 4 ), and Cu2(HCOO)4(2,6‐Me2pyrz)2 ( 5 ) have been synthesized and characterized by chemical analysis and IR and electronic spectro scopies. The three‐dimensional structure of compound 1 consists of –Cu–pyrz–Cu–pyrz– chains joined by bridging formate groups coordinated, in configuration syn‐anti, to two copper atoms. The coordination around the copper atom is orthorhombic with two Cu–O distances of 2.374(1) Å, two Cu–O of 1.952 Å and two Cu–N of 2.080 Å. Compound 5 is formed by molecular dimers with the [Cu2(μ‐HCOO)4] unit, two copper atoms and four syn‐syn fomate groups, and two ligands coordinated to the copper atoms in the axial positions. In compounds 2 and 3 chains of [Cu2(μ‐HCOO)4] dimers with pyrz or 2,3‐Me2pyrz as bridging ligands are formed. The EPR signal of 1 is orthorhombic (g = 2.23, 2.20 and 2.06). In the EPR spectra of 2 – 5 compounds the triplet (S = 1) signals are observed. The g?, g∥ and D values are been calculated. 相似文献
993.
S. Küppers 《Accreditation and quality assurance》1997,2(1):30-35
Any analytical data is used to provide information about a sample. The "possible error" of the measurement can be of extreme
importance in order to have complete information. The measurement uncertainty concept is a way to achieve quantitative information
about this "possible error" using an estimation procedure. On the basis of the analytical result, the chemist makes a decision
on the next step of the development process. If the uncertainty is unknown, the information is not complete; therefore this
decision might be impossible. The major problem for the in-process control (IPC) procedure is that not only the repeatability
but also the intermediate precision (which expresses the variations within laboratories related to different days, different
analysts, different equipment, etc.) has to be good enough to make a decision. Unfortunately, the statistical information
achieved from one single analytical run only gives information about the repeatability. This paper shows that the estimation
of the measurement uncertainty for IPC is a way to solve the problem and gives the necessary information about the quality
of the procedure. An example demonstrates that an estimate of uncertainty based on the standard deviations of an analytical
method gives a value similar to one based on the standard deviations obtained from a control chart. Therefore, the estimation
is both a very useful and also a very cost-effective tool. Though measurement uncertainty cannot replace validation in general,
it is a viable alternative to validation for all methods that will never be used routinely.
Received: 24 May 1996 Accepted: 10 August 1996 相似文献
994.
Strübing A Wittstock G Szargan R Werner G 《Analytical and bioanalytical chemistry》1996,356(3-4):274-278
Bismuth modified platinum electrodes are used for constant-potential amperometric determination of carbohydrates in flow systems. The monitored response is stable and reproducible over more than two days. An attempt is made to gain more detailed information about the characteristics of the modified layer by electrochemical methods and X-ray photoelectron spectroscopy. The response proved to be linear over the investigated concentration range (1.1–1200 mol/L) and detection limits for glucose and fructose were found to be 1.1 mol/L. 相似文献
995.
C. Sánchez-Pedreño M.Hernández Córdoba P.Viñas López-Pelegrín 《Microchemical Journal》1985,32(2):242-248
A kinetic method for the silver determination based on the catalytic effect of Ag(I) on the oxidation of o-dianisidine by persulfate at pH = 4.5 in the presence of 1,10-phenanthroline is proposed. Ag(I) can be determined by measuring the absorbance of the reaction product at 450 nm, using the fixed time method. Co(II) does not have a catalytic effect in the reaction, but in the simultaneous presence of silver and cobalt the reaction shows an induction period the length of which is related to the Ag/Co molar ratio. As a consequence, two new methods for the determination of cobalt and silver using the induction period method are proposed. The two methods for silver are applied to the determination of silver in lead. 相似文献
996.
As the first part of our studies on counter-current chromatography, the methodology for selecting suitable solvent systems was established based on detailed investigations of solubility and partition coefficients (log K) of macrolide antibiotic analogues. The solubility of two important macrolides, ascomycin and FK-506, was measured in a series of common solvents, where their polarities were ranked with dielectric constants. The partition coefficients of the two macrolides were compared in various binary, ternary, quaternary solvent systems. Hexane-tert.-butyl methyl ether-methanol-water system was selected based on suitable log K of solutes and hydrogen-bonding properties of solvents. In the further optimisation of composition proportions in the multicomponent solvent system, hexane-tert.-butyl methyl ether-methanol-water (1:3:6:5) showed the best solvent selectivity by giving the most prominent difference of partition coefficient (delta log K) between ascomycin and FK-506. With this solvent system, a baseline preparative separation of these two very closely related 23-membered macrolide antibiotics was successfully achieved by employing the newly introduced Quattro counter-current chromatograph. 相似文献
997.
N. Batbaryar D. Batsurén A. A. Semenov M. N. Sultankhodzhaev 《Chemistry of Natural Compounds》1993,29(5):658-661
In the course of a further study of the alkaloids of the epigeal part of Aconitum turczaninowiia new alkaloid has been isolated, which has been named turpelline. A structure for turpelline has been proposed on the basis of a study of its IR, mass, PMR, 13 C NMR, and 2D COSY spectra. 相似文献
998.
Mathias Höfler Jürgen Scheuren Detlef Spilker 《Journal of organometallic chemistry》1975,102(2):205-211
The complexes CpFe(CO)2SiBr3, CpFe(CO)2SiI3, CpFe(CO)2SiBr2(OMe), and CpFe(CO)2SiI(NH-cyclo-C6H11)2 are prepared by the reaction of CpFe(CO)2SiR3 (R = OMe, NH-cyclo-C6H11) with HBr, HI and CH3I. Treating CpFe(CO)2SiCl3 with a large excess of NaN3, KOCN or KSCN yields the first tri-pseudohalogensilyl—transition-metal-complexes. The compounds are characterized by IR and mass spectra. A new method of preparation of the already known complex CpFe(CO)2SiH3 is described starting from CpFe(CO)2SiCl3 and LiAlH4. 相似文献
999.
Szabó KJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(21):5268-5275
The synthetic scope of the allyl-palladium chemistry can be extended to involve electrophilic reagents. The greatest challenge in these reactions is the catalytic generation of an allyl-palladium intermediate incorporating a nucleophilic allyl moiety. A vast majority of the published reactions that involve palladium-catalyzed allylation of electrophiles proceed via bis(allyl)palladium intermediates. The eta(1)-moiety of the bis(allyl)palladium intermediates reacts with electrophiles, including aldehydes, imines, or Michael acceptors. Recently, catalytic electrophilic allylations via mono-allylpalladium complexes were also presented by employment of so-called "pincer complex" catalysts. 相似文献
1000.
Structural and biosynthetic studies of the metabolites isolated from various Colletotrichum species are reviewed. These fungi are destructive post-harvest pathogens on a wide range of plants including cereals, legumes and fruits. The review includes a detailed study of the biological activity of these metabolites and their role in the development of plant diseases. The literature in this field to the present is reviewed and 60 references are cited. 相似文献