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1.
2.
The stereochemistry of the cyclobutanones 1-7, resulted from the reaction of t-butylcyanoketene with bicyclo[2.2.1]heptene, bicyclo[2.2.1]heptadiene, 1,4 - dihydro - 1,4 - methanonaphthalene, 1,4 - dihydro - 9 - (1 - methylethylidene) - 1,4 - methanonaphthalene, 1,4 - dihydro - 1,4 - epoxynaphthalene, l,4,4a,8b - tetrahydro - 1,4 - methanobiphenylene (l,4,4a,8b) and 1,4,4a,8b - tetrahydro - 1,4 - methanobiphenylene(1,4,4aβ,8bβ) was established as having the cyclobutanone ring exo and the t-Bu group in the configuration. These findings represent a stereochemical argument in favour of a π2s + π2a reaction mode of t-butylcyanoketene to the above mentioned bicyclo[2.2.1]heptene derivatives. Observations regarding preservation of the original configurations of alkenes as well as the geometrical distorsion of the cyclobutanones are shortly discussed. 相似文献
3.
Alexander Sandvoß Henning Maag Constantin G. Daniliuc Dieter Schollmeyer Johannes M. Wahl 《Chemical science》2022,13(21):6297
Identification of an electron poor trifluoroacetophenone allows the formation of uniquely stable hemiketals from prochiral oxetanols. When exposed to a cobalt(ii) catalyst, efficient ring-opening to densely functionalized dioxolanes is observed. Mechanistic studies suggest an unprecedented redox process between the cobalt(ii) catalyst and the hemiketal that initiates the oxetane-opening. Based on this observation, a dynamic kinetic resolution of the transient hemiketals is explored that uses a Katsuki-type ligand for stereoinduction (up to 99 : 1 dr and 96 : 4 er) and allows a variety of 1,3-dioxolanes to be accessed (20 examples up to 98% yield).Desymmetrization of prochiral oxetanols via an electron-deficient hemiketal intermediate is achieved. Key to this process is the catalyst''s chiral recognition of one of the two hemiketal enantiomers enabling an efficient dynamic kinetic resolution. 相似文献
4.
Petre Constantin 《Communications in Mathematical Physics》1986,104(2):311-326
One of the central problems in the mathematical theory of turbulence is that of breakdown of smooth (indefinitely differentiable) solutions to the equations of motion. In 1934 J. Leray advanced the idea that turbulence may be related to the spontaneous appearance of singularities in solutions of the 3—D incompressible Navier-Stokes equations. The problem is still open. We show in this report that breakdown of smooth solutions to the 3—D incompressible slightly viscous (i.e. corresponding to high Reynolds numbers, or highly turbulent) Navier-Stokes equations cannot occur without breakdown in the corresponding solution of the incompressible Euler (ideal fluid) equation. We prove then that solutions of distorted Euler equations, which are equations closely related to the Euler equations for short term intervals, do breakdown.Sponsored by the United States Army under Contract No. DAAG29-80-C-0041, and partially supported by the National Science Foundation under Grant No. MCS-82-01599 相似文献
5.
We have studied the enhanced ionic conductivity of thin films of LiI evaporated onto a planar sapphire surface carrying interdigital Au-electrodes. The interface conductivity parallel to the surface was measured in situ for increasing film thickness, up to 3,000 Å. The specific conductivity of LiI in the first 300 Å — adjacent to the sapphire — was found to exceed the bulk conductivity of LiI by nearly one order of magnitude. From our observations we conclude that the specific conductivity of LiI decreases exponentially with distance from the sapphire surface reaching the bulk LiI-value only at a distance of 3,000 Å. The conductivity of a 350 Å thick film varies with temperature (25°CT120°C) in accordance with an activation energy of 0.40±0.04 eV. This is in good agreement with the activation energy of bulk LiI in the extrinsic region. 相似文献
6.
The Lorentz-violating isotropic modified Maxwell theory minimally coupled to standard Dirac theory is characterized by a single real dimensionless parameter which is taken to vanish for the case of the standard (Lorentz-invariant) theory. A finite domain of positive and negative values of this Lorentz-violating parameter is determined, in which microcausality and unitarity hold. The main focus of this article is on isotropic modified Maxwell theory, but similar results for an anisotropic nonbirefringent case are presented in Appendix A. 相似文献
7.
系统研究了霍尔赫鲁特铝电解池中SnO2基惰性阳极 (96%SnO2+2%Sb2O3+2%CuO)的电流效率,腐蚀性以及结构变化. 评价了各种操作参数(温度、电流密度、阴阳两级的距离、冰晶石量比、Al2O3 浓度和电解质组成)对电流效率和腐蚀性的影响. 相似文献
8.
Constantin JG Fris AR Appignanesi G Carignano M Szleifer I Corti H 《The European physical journal. E, Soft matter》2011,34(11):126
The structure of water clusters (H2O)n (n = 40 -200) and bulk water were examined by molecular dynamics simulations using the TIP4P-ice water model. The analysis of
the low-temperature structures in terms of the local structure index (LSI) showed a bimodal distribution. This finding supports
the two-state picture derived from the analysis of the inherent dynamics of bulk SPC/E water. The water molecules at the outer
interface of the coldest clusters are more structured than those in the inner core. The geometrical constraint of the interface
forces the surface molecules to lose one neighbor and adopt a local angular distribution of hydrogen bonds resembling that
found in the basal plane of ice Ih. 相似文献
9.
Let Φ′ be the strong dual of a nuclear Fréchet space Φ. In this paper we present regularity properties, weak convergence, and convergence in probability and in mean square of Φ′-valued stochastic evolution equations and convolutions with respect to Φ′-valued cadlag martingales. 相似文献
10.
Peter Constantin E Weinan Edriss S. Titi 《Communications in Mathematical Physics》1994,165(1):207-209
We give a simple proof of a result conjectured by Onsager [1] on energy conservation for weak solutions of Euler's equation. 相似文献