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Cem B. Yildiz Kinga I. Leszczyska Sandra Gonzlez‐Gallardo Michael Zimmer Akin Azizoglu Till Biskup Christopher W. M. Kay Volker Huch Henry S. Rzepa David Scheschkewitz 《Angewandte Chemie (International ed. in English)》2020,59(35):15087-15092
Main group analogues of cyclobutane‐1,3‐diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all‐silicon 1,3‐cyclobutanediyls as stable closed‐shell singlet species from the reversible reactions of cyclotrisilene c‐Si3Tip4 (Tip=2,4,6‐triisopropylphenyl) with the N‐heterocyclic silylenes c‐[(CR2CH2)(NtBu)2]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N‐heterocyclic silylene c‐(CH)2(NtBu)2Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3‐cyclobutanediyl intermediate. 相似文献
23.
Motivated by a recent paper of Liu and Ma, we describe a number of general WP-Bailey chains. We show that many of the existing
WP-Bailey chains (or branches of the WP-Bailey tree), including chains found by Andrews, Warnaar and Liu and Ma, arise as
special cases of these general WP-Bailey chains. We exhibit three new branches of the WP-Bailey tree, branches which also
follow as special cases of these general WP-Bailey chains. Finally, we describe a number of new transformation formulae for
basic hypergeometric series which arise as consequences of these new WP-Bailey chains. 相似文献
24.
Let be a lattice in a noncompact simple Lie Group G, where . Suppose acts analytically and ergodically on a compact manifold M preserving a unimodular rigid geometric structure (e.g. a connection and a volume). We show that either the action is isometric or there exists a "large image" linear representation of . Under an additional assumption on the dynamics of the action, we associate to a virtual arithmetic quotient of full entropy.
Received: December 14, 2000 相似文献
25.
L. Monz R. Hohmann H.-J. Kluge S. Kunze J. Lantzsch E.W. Otten G. Passler P. Senne J. Stenner K. Stratmann K. Swendt K. Zimmer G. Herrmann N. Trautmann K. Walter 《Spectrochimica Acta Part B: Atomic Spectroscopy》1993,48(14):1655-1671
Environmental assessment in the wake of a nuclear accident requires the rapid determination of the radiotoxic isotopes 89Sr and 90Sr. Useful measurements must be able to detect 108 atoms in the presence of about 1018 atoms of the stable, naturally occurring isotopes. This paper describes a new approach to this problem using resonance ionization spectroscopy in collinear geometry, combined with classical mass separation. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an isotopic selectivity of about 106. The ions are then neutralized by charge exchange and the resulting fast strontium atoms are selectively excited into high-lying atomic Rydberg states by narrow-band cw laser light in collinear geometry. The Rydberg atoms are then field-ionized and detected. Thus far, a total isotopic selectivity of S > 1010 and an overall efficiency of ξ = 5 × 10−6 have been achieved. The desired detection limit of 108 atoms 90Sr has been demonstrated with synthetic samples. 相似文献
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Using an a.c. arc and visible spectral lines a spectrographic method for the rapid determination of traces of Co, Cr, Ga.In, Pb and V in synthetic coal ashes has been worked out, in which the samples are burned in Al electrodes thus avoiding perturbation by cyanogen bands. With the help of intensity-time studies an exposure time of 10 sec was found giving optimum power of detection as well as optimum reproducibility. By a suitable choice of experimental conditions the background density was adjusted to a value which permitted making accurate background corrections and using the background as reference radiation at the same time. Variation of the method included the application of intermediate diaphragms and the use of Fe-lines as well as of the background as reference signals with and without background correction. The standard deviations as well as the tested concentration ranges are reported. 相似文献
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The thermolysis and/or photolysis of 3-(2-azidophenylmethylene)-4,5-dihydro-2-(3H)furanone offers a preparatively useful way towards the synthesis of indoles and quinolines. This method is superior over previously published methods which afforded these heterocycles in poor yields by the deoxygenative cyclization of 3-(2-nitrophenyImethylene)-4,5-dihydro-2-(3H)furanones. J. Heterocyclic Chem., 15 , 703 (1978) 相似文献
30.
Extensive LEED intensity-energy data have been collected for a Si{100}(1 × 1)H surface and dynamical theory LEED calculations have been performed using an ideal unreconstructed Si(100) surface to model this structure. Agreement between experiment and theory is good indicating that the probable structure for this surface does involve (weakly scattering) H atoms on the “dangling bonds” of an unreconstructed Si(100) surface, and that difficulties in achieving good agreement between experiment and theory for the clean Si{100}(2 × 1) surface is more probably due to deficiencies in the model structure than to deficiencies in the non-structural aspects of the LEED theory. 相似文献