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[reaction: see text] A reversal of diastereoselectivity was observed for novel 5-(trimethylsilyl)adamantan-2-ylidene (1c) with regard to 5-hydroxyadamantan-2-ylidene (1a). Ostensibly in intermolecular reactions, 5-substituted 2-adamantanylidenes (1) are sterically unbiased. However, inductive effects originating from the pendant group bend the divalent carbon bridge of 1 either toward (ERG's, e.g., -Si(CH(3))(3)) or away from (EWG's, e.g., -OH) the gamma-position. Hence, the more exposed side is more susceptible to intermolecular reaction and the other side concomitantly undergoes intramolecular 1,3-CH insertions more readily. 相似文献
33.
Properties of target species can be estimated by various means including interpolations in periodic charts. Interpolation is equivalent to numerical solution of the Laplace equation. A test of this equivalence, within some confidence level, for any N-atomic molecule surrounded by 4N nearest neighbors: the sum of the second differences of the data in all directions must be zero. Since very few molecules have 4N neighbors with known data, the test becomes: the sum of the averages of the second differences must be zero. The validity of these tests is explored. For radii of main-group atoms, and for internuclear separations of their diatomic combinations, the averages are different from zero and the sums of the averages are zero to within one if second-nearest neighbors are used. Dissociation potentials pass the tests but with larger scatter. Predictions for dissociation potentials, using iterative interpolation within boundaries on which there are known data, are reviewed. 相似文献
34.
Schmidt E Knoll L Welsch DG Zielonka M Konig F Sizmann A 《Physical review letters》2000,85(18):3801-3804
Quantum effects in N-bound solitons can be drastically enhanced compared to the fundamental soliton. In particular, the spectral photon-number correlations are much stronger. The formation of spectral domains of almost perfect positive and negative correlations is predicted. Criteria that are based on the Cauchy-Schwarz inequality are used for studying nonclassical correlations. Interferences between different soliton components of the N-bound solution being responsible for the strong changes in the coherent amplitude may also be a mechanism for the strong correlations. The results offer novel possibilities of producing light with highly nonclassical properties. 相似文献
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K. Knoll J. Schneider D. Buchholz G. Huttner 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4)
Abstract RP groups are useful cluster constituents: They warrant a detailed analysis of cluster reactions even in those cases where metal-metal bonds break and where, without these linking groups, the clusters would desintegrate. 相似文献
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Helmut Knoll 《国际化学动力学杂志》2008,40(2):59-65
Rate constants of the thermal cis → trans isomerization of azo dyes have been studied in aqueous P85 and F88 triblock copolymer solutions by means of microsecond flash photolysis. Inflection points or maxima of the nonlinear Arrhenius plots indicate microstructure changes around the “kinetic” probe molecules. Unidirectional interactions of micelle formation on reactivity are reflected by discontinuous change of rate constants at temperatures near the critical micellization temperatures (cmT) determined by means of probe‐free methods. Mutual interactions have been identified by means of significant differences between cmT and temperatures, where rate constants change discontinuously. The type of interactions depends on the properties of probe molecules and amphiphiles. Systems as studied in this work might be models of more complex biological reaction systems with temperature‐dependent microstructure changes. © 2007 Wiley Periodicals, Inc. 40: 59–65, 2007 相似文献
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Michael Sawodny Albert Schmidt Manfred Stamm Wolfgang Knoll Claus Urban Helmut Ringsdorf 《先进技术聚合物》1991,2(3):127-136
Stable monomolecular layers of a liquid-crystalline homopolymer bearing azobenzene chromophores in the mesogenic side groups could be prepared at the water–air interface by slow compression at room temperature. From the area per monomer unit of A0≈0.25 nm2 a structural model with tightly packed azobenzene groups oriented nearly parallel to the surface normal was deduced. After transfer to a solid support in a Y-type mode the obtained Langmuir–Blodgett–Kuhn (LBK) multilayer assemblies of varying thicknesses (from a double layer to a thick film of d = 238 nm, capable of guiding optical modes) were prepared and analyzed by X-ray reflection and optical evanescent wave techniques. A monolayer thickness of d0 = 2.52 nm, as well as the anisotropic index of refraction of these layers, could thus be evaluated. Photo-isomerization by UV-irradiation (at λ = (360±30)nm) was examined by UV-VIS absorption spectroscopy. X-ray reflectivity data of samples illuminated for 30 min showed a complete loss of the layered structure of the LBK samples. As a result strongly light-scattering films were obtained. Surface plasmon microscopy was used to demonstrate the usefulness of this photo-induced order–disorder transition for optical information storage. 相似文献