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151.
金属钨三键多核金属有机配合物高压拉曼及红外光谱研究 总被引:2,自引:0,他引:2
许振华 《光谱学与光谱分析》2001,21(5):596-598
研究了金属钨三键多核金属有机配合物 [Cl(CO) 2 (DPPE)WCC6 H4CCC6 H4NC]2 ReCl(CO) 3(DPPE =bis(diphenylphosphino)ethane,(Ph) 2 PCH2 CH2 P(Ph) 2 )不同压力下的拉曼和红外光谱 (最高压力约 5 0kbar)。配合物在 3 0kbar存在一压力诱导二级相变。金属钨三键伸缩振动ν(WC)压力相关 (dν/dp)在低压相区 ( 0 5 9cm-1·(kbar) -1)与高压相区 ( 0 0 4cm-1·(kbar) -1)差别很大 (约 15倍 )。在高压下 ,从基团Cl(CO) 2 (DPPE)WC中的金属钨W向COπ 轨道的π 反馈明显增强 ,WC的键强度减弱 ,力常数减小和ν(WC)降低 ;此效应与压力缩短WC键 ,增大力常数和增加ν(WC)的效应互相竞争。 相似文献
152.
Ralf Mayr‐Stein Michael Bolte 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(1):e19-e20
The crystal and molecular structure of 4‐dimethylaminopyridinium bromide, C7H11N2+.Br?, (I), is built up by hydrogen‐bonded dimers of crystallographic 222 symmetry and four short C—H...halogen contacts. It is remarkable that (I) and 4‐dimethylaminopyridinium chloride are not isostructural. 相似文献
153.
Caroline Joannesse Craig P. Johnston Louis C. Morrill Philip A. Woods Madeleine Kieffer Dipl.‐Chem. Tobias A. Nigst Prof. Herbert Mayr Dr. Tomas Lebl Prof. Douglas Philp Dr. Ryan A. Bragg Dr. Andrew D. Smith 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(8):2398-2408
The structural motif within a series of tetrahydropyrimidine‐based isothioureas necessary for generating high asymmetric induction in the asymmetric Steglich rearrangement of oxazolyl carbonates is fully explored, with crossover and dynamic 19F NMR experiments used to develop a mechanistic understanding of this transformation. 相似文献
154.
155.
Zhibin Huang Kevin A. Yuh Simon S. Lo John C. Grecula Steffen Sammet Christina L. Sammet Guang Jia Michael V. Knopp Qiang Wu Norman J. Beauchamp III William T.C. Yuh Roy Wang Nina A. Mayr 《Magnetic resonance imaging》2014
Purpose
To classify tumor imaging voxels at-risk for treatment failure within the heterogeneous cervical cancer using DCE MRI and determine optimal voxel's DCE threshold values at different treatment time points for early prediction of treatment failure.Material and Method
DCE-MRI from 102 patients with stage IB2–IVB cervical cancer was obtained at 3 different treatment time points: before (MRI 1) and during treatment (MRI 2 at 2–2.5 weeks and MRI 3 at 4–5 weeks). For each tumor voxel, the plateau signal intensity (SI) was derived from its time-SI curve from the DCE MRI. The optimal SI thresholds to classify the at-risk tumor voxels was determined by the maximal area under the curve using ROC analysis when varies SI value from 1.0 to 3.0 and correlates with treatment outcome.Results
The optimal SI thresholds for MRI 1, 2 and 3 were 2.2, 2.2 and 2.1 for significant differentiation between local recurrence/control, respectively, and 1.8, 2.1 and 2.2 for death/survival, respectively.Conclusion
Optimal SI thresholds are clinically validated to quantify at-risk tumor voxels which vary with time. A single universal threshold (SI = 1.9) was identified for all 3 treatment time points and remained significant for the early prediction of treatment failure. 相似文献156.
Industry as well as the private domain show an increasing interest to the field of mobile robotics. With a higher number of applications, the complexity of the required tasks rises, and therefore the community tends to use robots with many degrees of freedom (DOF). The present paper takes this topic up and focuses on challenges of the kinematical modeling of redundant, non-holonomic mobile robots by considering a 12 DOF platform. To reach an omnidirectional behaviour, the actuated wheels are diagonally mounted on the chassis. Well known problems resulting from this set-up are parametric singularities which unnecessarily restrict the motion of the mathematical model. As it turns out, this problem can be avoided by the use of a non-minimal parametrized model. An additional challenge results from the inverse kinematic (IK) problem on velocity level. The corresponding equations are highly underdetermined and, due to the non-holonomic wheels, not directly affected by the steering angle velocities. This problem is solved by performing a local optimization on acceleration level. Finally, simulation results are presented. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
157.
Dr. Johannes Ammer Dr. Christoph Nolte Prof. Dr. Konstantin Karaghiosoff Sebastian Thallmair Dr. Peter Mayer Prof. Dr. Regina de Vivie‐Riedle Prof. Dr. Herbert Mayr 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(43):14612-14630
The 1H NMR chemical shifts of the C(α)? H protons of arylmethyl triphenylphosphonium ions in CD2Cl2 solution strongly depend on the counteranions X?. The values for the benzhydryl derivatives Ph2CH? PPh3+ X?, for example, range from δH=8.25 (X?=Cl?) over 6.23 (X?=BF4?) to 5.72 ppm (X?=BPh4?). Similar, albeit weaker, counterion‐induced shifts are observed for the ortho‐protons of all aryl groups. Concentration‐dependent NMR studies show that the large shifts result from the deshielding of the protons by the anions, which decreases in the order Cl? > Br? ? BF4? > SbF6?. For the less bulky derivatives PhCH2? PPh3+ X?, we also find C? H???Ph interactions between C(α)? H and a phenyl group of the BPh4? anion, which result in upfield NMR chemical shifts of the C(α)? H protons. These interactions could also be observed in crystals of (p‐CF3‐C6H4)CH2? PPh3+ BPh4?. However, the dominant effects causing the counterion‐induced shifts in the NMR spectra are the C? H???X? hydrogen bonds between the phosphonium ion and anions, in particular Cl? or Br?. This observation contradicts earlier interpretations which assigned these shifts predominantly to the ring current of the BPh4? anions. The concentration dependence of the 1H NMR chemical shifts allowed us to determine the dissociation constants of the phosphonium salts in CD2Cl2 solution. The cation–anion interactions increase with the acidity of the C(α)? H protons and the basicity of the anion. The existence of C? H???X? hydrogen bonds between the cations and anions is confirmed by quantum chemical calculations of the ion pair structures, as well as by X‐ray analyses of the crystals. The IR spectra of the Cl? and Br? salts in CD2Cl2 solution show strong red‐shifts of the C? H stretch bands. The C? H stretch bands of the tetrafluoroborate salt PhCH2? PPh3+ BF4? in CD2Cl2, however, show a blue‐shift compared to the corresponding BPh4? salt. 相似文献
158.
Bernhard Lamprecht Elke Kraker Martin Sagmeister Stefan Köstler Nicole Galler Harald Ditlbacher Birgit Ungerböck Tobias Abel Torsten Mayr 《固体物理学:研究快报》2011,5(9):344-346
We present a novel optical sensor platform, combining monolithically integrated ring‐like sensor waveguides together with ring‐shaped thin‐film organic photodiodes (OPDs) on one substrate. The OPDs serve as integrated light detectors, simplifying the detection system by minimizing the number of required optical components. The waveguide structures, including a means of coupling light in and out of the waveguides, serve as sensing elements. The functionality of the concept is demonstrated by an integrated carbon dioxide sensor, utilizing absorbance as sensing principle. The integrated optical sensor platform is suitable for the parallel detection of multiple parameters in a single sensor chip using sensor arrays. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
159.
Jingjing Zhang Quan Chen Robert J. Mayer Jin‐Dong Yang Armin R. Ofial Jin‐Pei Cheng Herbert Mayr 《Angewandte Chemie (International ed. in English)》2020,59(30):12527-12533
The kinetics and stereochemistry of the reactions of iminium ions derived from cinnamaldehydes and MacMillan's imidazolidinones with diphenyldiazomethane and aryldiazomethanes were investigated experimentally and with DFT calculations. The reactions of diphenyldiazomethane with iminium ions derived from MacMillan's second‐generation catalysts gave 3‐aryl‐2,2‐diphenylcyclopropanecarbaldehydes with yields >90 % and enantiomeric ratios of ≥90:10. Predominantly 2:1 products were obtained from the corresponding reactions with monoaryldiazomethanes. The measured rate constants are in good agreement with the rate constants derived from the one‐center nucleophilicity parameters N and sN of diazomethanes and the one‐center electrophilicity parameters E of iminium ions as well as with quantum chemically calculated activation energies. 相似文献
160.
New In Situ Trapping Metalations of Functionalized Arenes and Heteroarenes with TMPLi in the Presence of ZnCl2 and Other Metal Salts
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M. Sc. Annette Frischmuth Dr. Maitane Fernández M. Sc. Nadja M. Barl M. Sc. Florian Achrainer Prof. Dr. Hendrik Zipse Dr. Guillaume Berionni Prof. Dr. Herbert Mayr Prof. Dr. Konstantin Karaghiosoff Prof. Dr. Paul Knochel 《Angewandte Chemie (International ed. in English)》2014,53(30):7928-7932
The addition of TMPLi to a mixture of an aromatic or heteroaromatic substrate with a metal salt such as MgCl2, ZnCl2, or CuCN at ?78 °C first leads to lithiation of the arene followed by transmetalation with the metal salt to afford functionalized organometallic compounds of Mg, Zn, or Cu. This in situ trapping method allows an expedited metalation (?78 °C, 5 min) of a range of sensitive pyridines (bearing a nitro, ester, or cyano group) and allows the preparation of kinetic regioisomers of functionalized aromatic compounds or heterocycles not otherwise available by standard metalating agents, such as TMPMgCl?LiCl or TMPZnCl?LiCl. 相似文献