An electron-diffraction study of the molecular structure of gaseous perbromyl fluoride and calculation of its force field and vibrational amplitudes

The molecular structure of FBrO₃ has been studied by gas-phase electron diffraction. Least-squares refinements of the molecular geometry using fixed spectroscopic amplitudes revealed two geometrical minima. Initially, the amplitudes employed were derived from diagonal force fields obtained by spectroscopic least-squares refinements to fit observed and calculated wave numbers; for each geometry there are two spectroscopic minima. In the lowest geometrical minimum the wave number agreement is poor, however, the introduction of the ∠OBrO/∠FBrO interaction force constant removed the discrepancies; the resulting force field is F(Br-O) = 6.92 ± 0.02 mdyn Å^?1F(Br-F) = 3.22 ± 0.03 mdyn Å^?1, F(∠OBrO) = 1.06 ± 0.02 mdyn Å, F(∠FBrO) = 0.81 ± 0.03 mdyn Å, F(∠OBrO/∠FBrO) = ?0.19 ± 0.02 mdyn Å. In the corresponding geometrical minimum r_g(Br-O) = 1.582 ± 0.001 Å, r_g(Br-F) = 1.708 ± 0.003 Å, r_α(∠OBrO) = 114.9 ± 0.3°, r_α(∠FBrO) = 103.3 ± 0.3°. Perpendicular amplitude correction coefficients, calculated for each force field employed, were used throughout to relate the interatomic distances through the r_α-structure. The geometries of the r_α^o- and r_e-structures are estimated.     

New (TMTSF)2X Derivatives: A Change in the Selenium Network Dimensionality Derived From the Molecular and Crystal Structures of (TMTSF)2(Fso3) [T=298K, 123K] and (TMTSF)2(Bro4) T=298K

Abstract

We report the first crystallographic analysis, as a function of temperature, of a TMTSF derivative. Both (TMTSF)₂(FSO₃) and (TMTSF)₂(BrO₄) are isostructural (triclinic, with space group PI) with superconducting (TMTSF)₂(ClO₄). (TMTSF)₂(FSO₃) undergoes a metal-to-insulator transition at 86-90K as observed by microwave conductivity, D.C. conductivity, and magnetic susceptibility. The crystal structure contains 2-dimensional sheets of short Se-Se contacts in the molecular stacking direction and perpendicular to the stacking direction. The temperature dependent variations in these contact distances appear to be of special importance in determining the conduction properties of these materials, and are observed to change in a surprising manner when (TMTSF)₂(FSO₃) is cooled (298 → 123K). The homoatomic Se separations within each TMTSF molecule appear to increase slightly, but not significantly. At the same time the entire 2-dimensional sheet of intermolecular (intra- and interstack) Se-Se contacts between TMTSF molecules contract quite anisotropically, which results in an increase in “dimensionality” of the Se-Se network. Hence, an increase in electrical conduction, in the absence of insulating phenomena, over the temperature range 298 → 123K is not surprising. The intermolecular Se-Se contact distances in (TMTSF)₂(BrO₄) are significantly longer than in (TMTSF)₂(FSO₃) which suggests that the room temperature electrical conductivity of the (BrO₄)^? salt may be diminished compared to the (FSO₃)^? analogue.     

Higher order symmetrizer and application to an unusual transport equation

We study a class of stationary transport equation with nonlocal low-order tems We obtain the existence and uniqueness of a solution in sobolev spaces     

求解复杂湍流的非线性涡黏性系数模型和代数应力模型

非线性涡黏性系数模型和代数应力模型联系了线性涡黏性系数湍流模型和完整的微分 雷诺应力模型.随着它们受到日益关注,其形式也越来越多样化.本篇综述的目的是对这些模 型加以总结并比较它们之间的共同点及不同之处,指出它们与完整微分雷诺应力模型之间的 关系,以及相对于线性涡黏性系数模型而言它们在预报流场上所具有的优势.     

Substitution and addition reactions of organic substrates with hypofluorous acid

The chemical reactions of hypofluorous acid with aromatic and olefinic substrates show considerable variety. Hypofluorous acid reacts with naphthalene to give 1-naphthol, 2-naphthol and 1,4-naphtho-quinone; with benzo[b]thiophen to give the 1,1-dioxide; with trans-stilbene to give threo-2-fluoro-1-hydroxy-1, 2-diphenylethane, benzophenone and diphenylacetaldehyde; and with cholesteryl acetate to give the two epoxides (α:β = 6.3:1) and two fluorohydrins (6β-fluoro-5β-o1 and 5α-fluoro-6β-o1).     

PegPhos: a monodentate phosphoramidite ligand for enantioselective rhodium-catalysed hydrogenation in water

A BICOL derived monodentate phosphoramidite ligand gives ee's up to 89% in the enantioselective Rh-catalysed hydrogenation of N-acyl dehydroalanine using water as the solvent.