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71.
Lothar Metzger Günter G. Willems und Rolf Neeb 《Fresenius' Journal of Analytical Chemistry》1978,292(1):20-22
Zusammenfassung Die starke Temperaturabhängigkeit des polarographischen Zinn(II/0)-Signals in Lösungen des vierwertigen Zinns ermöglicht bei –32° C in methanolischer salzsaurer Grundlösung die Bestimmung des Bleis neben hohem Zinnüberschuß. Eine Anwendung des Verfahrens zur wechselstrompolarographischen Bestimmung des Bleis in Rohzinn wird beschrieben.
Investigations on the simultaneous electrochemical determination of lead and tinII. Polarographic determination of lead in the presence of tin at lower temperatures
Summary The strong temperature dependence of the polarographic tin(II/0) signal in solutions containing tin(IV) renders possible the determination of lead in the presence of a high excess of tin at working temperatures of –32° C in hydrochloric methanol as supporting electrolyte solution. An application of the procedure to the ac-polarographic determination of lead in crude tin is described.
Die vorliegende Arbeit wurde in dankenswerter Weise durch Mittel der Deutschen Forschungsgemeinschaft und des Verbandes der Chemischen Industrie ermöglicht. 相似文献
72.
Investigation of the complexing of Na+, K+, Ca2+ and Ba2+ with some uncharged ligands by 13C-chemical shift and spin-lattice relaxation time measurements The influence of Na+, K+, Ca2+ and Ba2+ ions on 13C chemical shifts and on spin-lattice relaxation times of some electrically neutral ion carriers was investigated. In the solvents CD3CN and CD3OD and in presence of an excess of metal ions ligand 4 (see the Scheme) forms complexes of 1:1 stoichiometry. All four oxygen atoms of the ligand as well as solvent molecules take part in the coordination. In CDCl3 as solvent, for all ions investigated except sodium, only 1:2 complexes (metal/ligand) were observed with 4 . Sodium ions form both 1:1 and 1:2 complexes in this solvent. In the 1:2 complexes of the investigated monovalent ions only one, in those of the divalent ions both amide carbonyl groups of ligand 4 take part in the coordination. 相似文献
73.
On the Reactions of CH3OCl, CF3OCl, CF3OF, and CF3OH with the Superacid System HF/MF5 (M = As, Sb). Preparation and Characterization of CH3OCl(H)+MF6? and CF3OCl(H)+MF6? The preparation of the chlorine oxoniumsalts CH3OCl(H)+MF6? and CF3OCl(H)+MF6? by protonation of CH3OCl and CF3OCl in the superacid solution of HF/MF5 (M = As, Sb) is described. However CF3OF and CF3OH have not been protonated under the same conditions. In the case of CF3OH the formation of F2CO · MF5 is observed. The novel compounds are characterized by nmr- and vibrational spectroscopy. 相似文献
74.
The linear dichroic absorption spectrum of 1,3,6,8-trans-15, 16-hexamethyl-dihydropyrene has been measured in stretched polyethylene at 77K, and CNDO-CI calculations with inclusion of singly and doubly excited configurations have been carried out on a series of alkyl bridged [14] annulenes with pyrene- and anthracene-shaped perimeters. Transitions to e3g → e4u type 1B states are well described, and the results indicate that additional low-energy excited states originate from e3g→ e5g and e2u → e4u type configurations interacting strongly with doubly excited configurations of the e3g, e3g → e4u, e4u type. The second excited singlet state responsible for the weak transition observed between the 1L bands may be assigned to one of these additional states, but it is probably of complex nature, similar to the ‘phantom’ state in linear polyenes. 相似文献
75.
The anomalous reactivity of the bicyclo [2.2.1] heptene double bond is interpreted in terms of hyperconjugative effects, leading to an exceptionally low endo out-of-plane deformation potential. 相似文献
76.
Cooperative effects in binuclear zirconocenes: Their synthesis and use as catalyst in propene polymerization 总被引:3,自引:0,他引:3
Stephan Jüngling Rolf MüllhauptHerbert Plenio 《Journal of organometallic chemistry》1993,460(2):191-195
The mono- and bis-cyclopentadienyl compounds 1-(Cp″)-4-(CH3)C6H4 (1) and 1, 4-(Cp″)2C6H4 (2) (Cp″ = 3,4-dimethylcyclopenta-1,3-diene-1-yl) have been synthesized. The reactions of the lithium salts of 1 and 2 with CpZrCl3 · dme (dme = dimethoxyethane) and Cp*ZrCl3(CP* = C5(CH3)5) yielded the mono- and bi-nuclear bridged zirconocenes 1-(Cp″ZrCpCl2)-4-(CH3)C6H4 (3), 1,4-(Cp″ZrCpCl2)2C6H4 (4) and 1,4-(Cp″ZrCp*Cl2)2C6H4 (5). When activated with methylaluminoxane (MAO), the mono- and bi-nuclear zirconocenes 3 and 4 catalyse the polymerization of propene. The influence of the catalyst composition on the polymerization kinetics and molecular weight is discussed. 相似文献
77.
(–)-Carbovir ((–)- 1 ) was synthesized via the cyclic carbonate 2 in four steps starting from enantiomerically enriched (–)-(S)-(cyclopent-2-enyl)methanol ((–)- 3 ). 相似文献
78.
The existence of two transitions with opposite MCD in the 38000–45000 cm?1 absorption of thiophene is demonstrated. The B-term for the lowest transition is negative, while it is positive for the higher one. Quantum mechanical calculations in the π-electron approximation resulted in energies, oscillator strengths and MCD terms in good agreement with the observed spectra. 相似文献
79.
Simultaneous determination of ondansetron and tropisetron in human plasma using HPLC with UV detection 总被引:4,自引:0,他引:4
Bauer S Störmer E Kaiser R Tremblay PB Brockmöller J Roots I 《Biomedical chromatography : BMC》2002,16(3):187-190
A rapid and sensitive HPLC method for the simultaneous quantitation of ondansetron and tropisetron, two serotonin (5-HT) receptor antagonists frequently used in treatment and prevention of nausea and emesis, is described. The procedure involves liquid-liquid extraction of human plasma with dichloromethane coupled with reversed-phase HPLC and UV detection. The lower limits of quantification (LOQ) were 0.62 ng/mL for ondansetron and 1.25 ng/mL or tropisetron. Intra- and inter-assay coefficients of variation ranged from 1.5 to 7.5% and 5.3 to 13.7%, respectively. The sensitivity and precision were sufficient for determination of plasma concentrations after therapeutic administration of both drugs and the method can be used for the estimation of pharmacokinetic parameters. 相似文献
80.
Stephan Jüngling Rolf Mülhaupt Udo Stehling Hans-Herbert Brintzinger David Fischer Franz Langhauser 《Journal of polymer science. Part A, Polymer chemistry》1995,33(8):1305-1317
Propene was polymerized at 40°C and 2-bar propene in toluene using methylalumoxane (MAO) activated rac-Me2Si(Benz[e]Indenyl)2ZrCl2 ( BI ) and rac-Me2Si(2-Me-Benz[e]Indenyl)2ZrCl2 ( MBI ). Catalyst BI /MAO polymerizes propene with high activity to afford low molecular weight polypropylene, whereas MBI /MAO is less active and produces high molecular weight polypropylene. Variation of reaction conditions such as propene concentration, temperature, concentration of catalyst components, and addition of hydrogen reveals that the lower molecular weight polypropylene produced with BI /MAO results from chain transfer to propene monomer following a 2,1-insertion. A large fraction of both metallocene catalyst systems is deactivated upon 2,1-insertion. Such dormant sites can be reactivated by H2-addition, which affords active metallocene hydrides. This effect of H2-addition is reflected by a decreasing content of head-to-head enchainment and the formation of polypropylene with n-butyl end groups. Both catalysts show a strong dependence of activity on propene concentration that indicates a formal reaction order of 1.7 with respect to propene. MBI /MAO shows a much higher dependence of the activity on temperature than BI /MAO. At elevated temperatures, MBI /MAO polymerizes propene faster than BI /MAO. © 1995 John Wiley & Sons, Inc. 相似文献