Die Schwingungsspektren des Chlortrimethylammonium-chlorids und -hexachloroantimonats(V)

Inhaitsübersicht. Die Schwingungsspektren von (CH₃)₃NCI₂ (I) und (CH₃)₃NCl⁺SbCI₆^– (II) wurden aufgenommen und im Hinblick auf die N—Cl-Bindungsverhältnisse diskutiert. The Vibrational Spectra of Chlorotrimethylammonium Chloride and Hexachloroantimonate(V) Abstract. The vibrational spectra of (CH₃)₃NCl₂ (I) und (CH₃)₃NCl⁺SbCl₆^– (II) are measured and discussed in view of the N-Cl bonds. Die IR-Spektren der nach [9] dargestellten Verbindungen wurden als Verreibungen in Nujol bzw. Hostaflonöl mit einem linear in Wellenzahlen registrierenden IR-Spektrophotometer PE 457 (Perkin Elmer) aufgenommen. Die Raman-Spektren wurden mit einem Coderg-Laser-Gerät PHO vermessen. Zur Anregung wurde die 4880 Å-Linie eines Argon-Gaslasers verwendet.     

World-wide comparison on the quality of analytical determinations of PCDDs/PCDFs and dioxin-like PCBs in food

Interlaboratory comparsion exercises on the determination of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) and dioxin-like polychlorinated biphenyls (PCBs) in three natural foodstuffs have been performed annually since 2000 by the Norwegian Institute of Public Health. Up to 77 laboratories from 24 countries world-wide have reported results. The data have been statistically analysed in order to assess the comparability of both the reported individual congener concentrations and the calculated toxic equivalents (TEQ). Due to the low concentrations of PCDDs/PCDFs and dioxin-like PCBs in food, the treatment of congeners reported as “not detected” and the identification of outliers, influence the estimation of the consensus values considerably. Based on the experiences from the first two rounds, an approach for calculation of the consensus values was established, resulting in a non-skewed distribution of data. The relative standard deviation of consensus TEQs was 13–32% for PCDDs/PCDFs and 11–45% for PCBs. Z-scores were calculated for PCDD/PCDF-TEQs using a target value of ±20% for the deviation. For food samples with a PCDD/PCDF contamination of more than half of the EU maximum level, 63–87% of the participants achieved Z-scores ±1, while for low contaminated foodstuffs about 60% of the participants had Z-scores of ±2. After four rounds of interlaboratory comparisons it can be concluded that there is a good comparability of the analytical data for dioxins and dioxin-like PCBs in food at higher contamination levels. However, the laboratories need to improve their performance when determining levels in food with low contamination of dioxin-like compounds, due to the increasing demand for analyses of such food items. The importance of determining dioxin-like PCBs is demonstrated by their large contribution to the total TEQ, especially in food from the marine environment.     

Asymmetry of bremsstrahlung from polarized electrons

The triply differential cross section of unpolarized bremsstrahlung produced by polarized electrons in the Coulomb field of a nucleus is calculated with the aid of Sommerfeld-Maue wave functions. The photon asymmetry originating from transversely polarized electrons is calculated for various values of energies and angles, in particular for the parameters of recent experiments. As a function of the atomic number Z of the target nucleus, the asymmetry shows a distinct deviation from a linear dependence, in contrast to a previous calculation exact to lowest order in the Coulomb parameter Z/137. The cross-section formula is integrated numerically over the angles of the outgoing electrons to obtain the photon asymmetry observed in non-coincidence experiments.     

Direct carbocyclization of aldehydes with alkynes: combining gold catalysis with aminocatalysis

A combination of gold(I) complexes and amine bases catalyzes the 5-exo-dig cyclization of formyl alkynes. This direct alpha-functionalization of aldehydes with unactivated alkynes does not involve the use of preformed enol equivalents.     

Dynamics of Articulated Structures. Part I. Theory

ABSTRACT

A finite element based method is developed for geometrically nonlinear dynamic analysis of spatial articulated structures; i.e., structures in which kinematic connections permit large relative displacement between components that undergo small elastic deformation. Vibration and static correction modes are used to account for linear elastic deformation of components. Kinematic constraints between components are used to define boundary conditions for vibration analysis and loads for static correction mode analysis. Constraint equations between flexible bodies are derived in a systematic way and a Lagrange multiplier formulation is used to generate the coupled large displacement-small deformation equations of motion. A lumped mass finite element structural analysis formulation is used to generate deformation modes. An intermediate-processor is used to calculate time-independent terms in the equations of motion and to generate input data for a large-scale dynamic analysis code that includes coupled effects of geometric nonlinearity and elastic deformation. Examples are presented and the effects of deformation mode selection on dynamic prediction are analyzed in Part II of the paper.     

Exchange interaction effects in the crossing of spin-polarized Landau levels in a silicon-germanium heterostructure: transition into a ferromagnetic state

The crossing of spin-split Landau levels in a Si/SiGe heterostructure is investigated by means of magneto-transport experiments in tilted magnetic fields. We observe a transition from a paramagnetic into a fully spin polarized state. During the transition strongly enhanced maxima in the transverse resistivity ρ_xx appear when the parallel field component is oriented along the Hall bar. We assign this effect to an energy level structure strongly modified by exchange interaction effects between different Landau levels. Surprisingly the maximum in ρ_xx totally disappears when the parallel field component is perpendicular to the Hall bar.     

Photoinduced C(sp3)–H sulfination empowers the direct and chemoselective introduction of the sulfonyl group

Direct installation of the sulfinate group by the functionalization of unreactive aliphatic C–H bonds can provide access to most classes of organosulfur compounds, because of the central position of sulfinates as sulfonyl group linchpins. Despite the importance of the sulfonyl group in synthesis, medicine, and materials science, a direct C(sp³)–H sulfination reaction that can convert abundant aliphatic C–H bonds to sulfinates has remained elusive, due to the reactivity of sulfinates that are incompatible with typical oxidation-driven C–H functionalization approaches. We report herein a photoinduced C(sp³)–H sulfination reaction that is mediated by sodium metabisulfite and enables access to a variety of sulfinates. The reaction proceeds with high chemoselectivity and moderate to good regioselectivity, affording only monosulfination products and can be used for a solvent-controlled regiodivergent distal C(sp³)–H functionalization.

The photoinduced C–H sulfination of abundant aliphatic C–H bonds provides direct access to all major classes of organosulfur compounds via the intermediacy of synthetically versatile sulfinate salts.     

Synthese und Struktur von [Re(NH)Cl2(PMe2Ph)3][TaCl6] und [(Me2PhP)3Cl2Re≡N]2VOCl2

Synthesis and Structure of [Re(NH)Cl₂(PMe₂Ph)₃][TaCl₆] and [(Me₂PhP)₃Cl₂Re≡N]₂VOCl₂ The products of the reaction of ReNCl₂(PMe₂Ph)₃ with TaCl₅ are dependent on the solvent. In CH₂Cl₂ the solvent protonates the nitrido ligand to yield [Re(NH)Cl₂(PMe₂Ph)₃][TaCl₆] as air-stable, reddish brown needles with the space group P2₁/n and a = 1213.8(3), b = 1358.0(2), c = 2165.9(4) pm, β = 92.88(1)°, Z = 4. The Re atom of the cation exhibits an octahedral coordination with the phosphine ligands in meridional arrangement. The imido ligand is in trans-position to a Cl atom with a distance Re–N = 170.4(4) pm. When the reaction is carried out in toluene the dinuclear nitrido complex [Re(NTaCl₅)Cl₂(PMe₂Ph)₃] is obtained instead. The reaction of ReNCl₂(PMe₂Ph)₃ with VCl₃(THF)₃ in toluene affords the threenuclear complex [Re₂N₂Cl₄(PMe₂Ph)₅]VCl₃, which upon crystallization at air gives air-stable, reddish-brown crystals of [(Me₂PhP)₃Cl₂ReN]₂VOCl₂. They crystallize in the monoclinic space group P2₁ with a = 1519.2(5), b = 1257.1(1), c = 1564.3(6) pm, β = 102.86(2)°, and Z = 2. The threenuclear complex shows an almost linear arrangement Re≡N–V–N≡Re with distances Re–N 171(2) pm and V–N of 209(2) pm.