排序方式: 共有40条查询结果,搜索用时 31 毫秒
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Frank Hoffmann Lothar Jäger Carola Griehl 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):299-309
The reactions of diphenoxyphosphoryl chloride ((PhO) 2 P(O)Cl) and different chlorophosphonium salts ([R 3 PCl]X, R = (CH 3 ) 2 N, pyrrolidine, X = PF 6 m , BF 4 m ), respectively, with 7-aza-1-hydroxybenzotriazole (HOAt), 1-hydroxybenzotriazole (HOBt), hydroximinomalonitrile (HOxDCO), and ethyl hydroximinocyanoacetate (HOxO) are described. The structures of the new compounds, which are useful coupling reagents for epimerization-free peptide segment condensation, are discussed on the basis of their 1 H, 13 C, 31 P NMR, and IR spectra. The reactions of (PhO) 2 P(O)Cl lead to mixtures of O - and N -phosphorylated isomers of varying ratios. Contrary, reactions of chlorophosphonium salts yield exclusively one isomer. 相似文献
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火焰原子吸收光谱法测定钙盐试剂中的痕量镉 总被引:7,自引:1,他引:6
采用巯基棉分离富集钙盐试剂中的前量镉,用火焰原子吸收光谱法进行测定。方法简便、快速,结果满意。样品测定的相对标准偏差均小于4.81%。 相似文献
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Fractionation studies of mercury in soils and sediments: A review of the chemical reagents used for mercury extraction 总被引:3,自引:0,他引:3
Mercury in contaminated soils and sediments could be extracted by various chemical reagents in order to determine the different mercury species and partitions, providing useful information of toxicology, bioavailability and biogeochemical reactivity. Unfortunately, at present, neither specific extractants nor standard protocols exist for the isolation of particular mercury species. Although there has been considerable research focused on reagents for extracting mercury species, there is still little consensus. Thus, workers are advised to select the most appropriate reagent based on the nature of their sample, and to take all possible steps to validate the analyses performed. Therefore, the aim of this paper is to review the current reagents used for determining total mercury and its speciation as well as fractionation such as methylmercury, ethylmercury, elemental mercury, mercury sulphide and organically bound mercury by supposed selective (one reagent) and sequential (several reagents) extractions. The gathering information presented here bring to light the need for standard protocol for which the used chemical reagents should take into account the particular chemistry of mercury associated with specific properties of soil and sediment. Beside this required scheme, appropriate reference materials are also demanded. 相似文献
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《Analytical letters》2012,45(15):1783-1792
Abstract This report demonstrates that immobilized trimethylsilane is an appropriate reference standard for MASSCP-13C NMR studies of reagents immobilized on silica gel. An example is presented which shows that the immobilized trimethylsilane exhibits many of the advantages as a reference for these solid samples as does tetramethylsilane for liquid samples. It is further shown that pure solids may interact with an immobilized phase and produce significant spectral changes and thus are not appropriate as reference standards. 相似文献
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A novel rearrangement of bicyclic ketals was investigated by using AcCl-NaI and MgBr2-Ac2O. Mono- and diacetylated products were isolated from these catalyst systems. Details of the chemistry are discussed. 相似文献
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Derivatization of substances,separated on thin-layer plates,by means of an automatic spraying device
F. Kreuzig 《Chromatographia》1980,13(4):238-240
Summary An accurate and reproducible derivatization of substances, separated on TLC- and HPTLC-plates, can be achieved by mechanized spraying. The plate is moved horizontally to and fro, whilst the spraying vessel is driven up and down. The extent of movement and distance of the vessel from the plate are both adjustable. 相似文献
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The theoretical consideration of the sponteneous emission of γ-gravitons by excited nuclei lead us to the conclusion about the principle possibility of γ-graviton detection from cosmic and laboratory sources. The γ-graviton astronomy and geophysics can give new information about cosmic and geophysical processes. 相似文献
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P. Carmona 《光谱学快报》2013,46(8):645-653
Abstract Infrared spectra of whewellite (calcium oxalate monohydrate) have been recorded at 300 and 90°K in the 4000–2000 cm?1 range in order to investigate the factors determining the band breadth and structure. On the basis of the HOD and bending D2O fundamentals details of the whewellite crystal structure concerning the symmetry of water molecules and the strength and symmetry of the hydrogen bonds are also discussed. 相似文献
10.
Matthias Westerhausen Prof. Dr. 《无机化学与普通化学杂志》2009,635(1):13-32
The organocalcium chemistry developed vastly during the last decade. The preparation of the organocalcium compounds via direct synthesis (insertion of Ca into a C‐X bond of phenyl halides, Grignard reaction) affords skilful procedures due to the inertia of the calcium metal and the extreme reactivity of the organocalcium derivatives. Further suitable preparative methods include metathesis reactions of CaX2 with KR or LiR, metallation reactions of H‐acidic substrates, metal‐halogen exchange reactions, and transmetallation of heavy main group atoms in their compounds with calcium metal. Possibilities to stabilize organocalcium compounds include steric shielding by bulky ligands at the periphery and electronic reduction of the nucleophilicity of the calcium‐bound carbanions. Selected applications in catalysis such as hydrophosphination are also mentioned. Very recent developments and challenges in the preparation of alkaline earth metal(I) compounds are presented as well. Concepts to overcome the rather large atomization energies of the metals are discussed. 相似文献