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排序方式: 共有128条查询结果,搜索用时 15 毫秒
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P.H.M. Budzelaar H.J. Alberts-Jansen K. Mollema J. Boersma G.J.M. van der Kerk A.L. Spek A.J.M. Duisenberg 《Journal of organometallic chemistry》1983,243(2):137-148
The stabilities of simple and internally coordinated organozinc-transition metal compounds towards disproportionation have been investigated by the microwave titration technique. Simple alkyl- and aryl-derivatives disproportionate to such an extent as to preclude isolation. Internal coordination was found to stabilize the asymmetric compounds, and several derivatives containing the dimethylaminopropyl group were isolated. The crystal structure of one of them, Me2N(CH2)3-ZnW(Cp)(CO)3, was determined by a single-crystal X-ray study. The crystals are orthorhombic, space group P212121, with four molecular units in a cell with parameters a 8.406(1), b 12.179(2) and c 16.642(2) Å. The structure was solved by standard Patterson and Fourier techniques. The refinement, with anisotropic temperature factors for the two heavy atoms, converged at RF = 0.092 (RwF = 0.089) for 1536 observed reflections with I>2.5σ(I). The molecule consists of a central tungsten atom, surrounded in a tetragonal pyramidal fashion by a cyclopentadienyl group in the apical position and three carbon monoxyde molecules and a zinc atom occupying the basal positions. The zinc atom is three-coordinate, being surrounded by the tungsten atom and the chelating dimethylaminopropyl group; there is, however, a short intermolecular contact between zinc and a carbonyl oxygen atom at 2.61(3) Å. 相似文献
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Paramagnetic species are formed when LiBipy is treated with various alkylzinc halides at ?100°C and the ESR spectra are discussed. The observation that the half-life times of the radical species appear to depend only on the nature of the alkyl group bound to zinc proves that monoalkylzinc-2,2′-bipyridine complexes are formed. The nature of the bonding between zinc and 2,2′-bipyridine is discussed. 相似文献
5.
An enantioselective gas chromatography (GC) method has been developed and validated for determination of the enantiomers of citronellol in kinetic resolution experiments. S-(-)-beta-Citronellol is a precursor of rose oxide. After solid-phase extraction (SPE) with ethyl acetate, the enantiomers of R-(+)-beta-citronellol and S-(-)-beta-citronellol and their corresponding acetate- and butyrate esters were separated through enantioselective GC respectively. The method was validated and found to be reproducible, specific, accurate, and precise. Analyte recoveries and detection limits were also determined. The applicability of this method was shown in a kinetic resolution experiment using lipase A of Bacillus subtilis. 相似文献
6.
H.K. Hofstee J. Boersma G.J.M. Van Der Kerk 《Journal of organometallic chemistry》1978,144(2):255-261
The reaction of diarylzinc compounds with copper(I) salts is an excellent way of preparing stable arylcopper compounds in quantitative yields. These compounds have been characterized by IR, and by 1H and 13C NMR spectroscopy. Cryoscopic molecular weight determinations show phenylcopper to be polymeric and 2-methylphenylcopper and 2,6-dimethylphenylcopper to be tetrameric in benzene. The compounds are believed to contain aryl groups bridging two copper atoms. Evidence is presented for rotation of these aryl groups around the C(1)—C(4) axis. 相似文献
7.
Chládková K Escudero P Boersma P 《The Journal of the Acoustical Society of America》2011,130(1):416-428
This paper examines four acoustic properties (duration F0, F1, and F2) of the monophthongal vowels of Iberian Spanish (IS) from Madrid and Peruvian Spanish (PS) from Lima in various consonantal contexts (/s/, /f/, /t/, /p/, and /k/) and in various phrasal contexts (in isolated words and sentence-internally). Acoustic measurements on 39 speakers, balanced by dialect and gender, can be generalized to the following differences between the two dialects. The vowel /a/ has a lower first formant in PS than in IS by 6.3%. The vowels /e/ and /o/ have more peripheral second-formant (F2) values in PS than in IS by about 4%. The consonant /s/ causes more centralization of the F2 of neighboring vowels in IS than in PS. No dialectal differences are found for the effect of phrasal context. Next to the between-dialect differences in the vowels, the present study finds that /s/ has a higher spectral center of gravity in PS than in IS by about 10%, that PS speakers speak slower than IS speakers by about 9%, and that Spanish-speaking women speak slower than Spanish-speaking men by about 5% (irrespective of dialect). 相似文献
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High speed PIV applied to aerodynamic noise investigation 总被引:1,自引:0,他引:1
V. Koschatzky P. D. Moore J. Westerweel F. Scarano B. J. Boersma 《Experiments in fluids》2011,50(4):863-876
In this paper, we study the acoustic emissions of the flow over a rectangular cavity. Especially, we investigate the possibility
of estimating the acoustic emission by analysis of PIV data. Such a possibility is appealing, since it would allow to directly
relate the flow behavior to the aerodynamic noise production. This will help considerably in understanding the noise production
mechanisms and to investigate the possible ways of reducing it. In this study, we consider an open cavity with an aspect ratio
between its length and depth of 2 at a Reynolds number of 2.4 × 104 and 3.0 × 104 based on the cavity length. The study is carried out combining high speed two-dimensional PIV, wall pressure measurements
and sound measurements. The pressure field is computed from the PIV data. Curle’s analogy is applied to obtain the acoustic
pressure field. The pressure measurements on the wall of the cavity and the sound measurements are then used to validate the
results obtained from PIV and check the range of validity of this approach. This study demonstrated that the technique is
able to quantify the acoustic emissions from the cavity and is promising especially for capturing the tonal components on
the sound emission. 相似文献
10.
We present a unified treatment of theslicing (3+1) andthreading (1+3) decompositions of spacetime in terms of foliations. It is well-known how to decompose the metric and connection in the slicing picture; this is at the heart of any initial-value problem in general relativity. We describe here the analogous problem in the threading picture, recovering the recent results of Perjés onparametric manifolds. 相似文献