Synthesis of diastereo- and enantiomerically pure α-amino-γ-oxo acid esters by reaction of acyliminoacetates with enamines derived from 6-membered ketones

A new efficient diastereo- and enantioselective synthesis of α-amino-γ-oxo acid esters by reaction of acyliminoacetates with enamines is described. By employing the concept of double stereodifferentiation, complete asymmetric induction (de ≧99.9%) for the C-C bond formation is obtained. Desulphurization of a sulphur containing product leads to the corresponding acyclic amino acid derivatives. The virtually complete anti -diastereo- and enantioselectivities are interpreted by a Diels-Alder like transition state.     

Kristallographische,elektronische und magnetische Eigenschaften des Spinells Li[Mn2]O4

The formation of the spinel Li[Mn₂]O₄ (2) from Li₂CO₃ and Mn₃O₄ by solid state reaction was examined as a function of temperature. The lattice parameter, the oxygen parameter and the infrared spectrum as well as the temperature dependence of the resistivity, the Seebeck coefficient, the magnetic properties and neutron diffraction have been studied.     

Allene nu9 and nu10: Low-Temperature Measurements of Line Intensity

We report laboratory intensity measurements for the weak nu9 (998.8 cm-1) and intense nu10 (841.1 cm-1) bands of allene. Allene is predicted to be a constituent of Titan's atmosphere, and measurements of its abundance would yield important information about the atmospheric chemistry of that body. Spectra were obtained at a temperature of 200 K (approximating Titan conditions) using the high-resolution FTS instrument at Kitt-Peak National Observatory's McMath-Pierce observatory. A total of 505 nu9 and 687 nu10 line intensities were fit using a least-squares method to accurately determine two sets of transition dipole moments. Integrated band intensities computed utilizing the fitted parameters were found to be 36 +/- 4% cm-2 atm-1 and 301 +/- 4% cm-2 atm-1 for nu9 and nu10, respectively, at 200 K. Copyright 1999 Academic Press.     

On the dimension of the cartesian product of relations and orders

It is known that for incidence structures and , max , wheref dim stands for Ferrers relation. We shall show that under additional assumptions on and , both bounds can be improved. Especially it will be shown that the square of a three-dimensional ordered set is at least four-dimensional.     

Rb3LnCl6 · 2 H2O (Ln = La?Nd): Darstellung,Kristallstruktur und thermisches Verhalten

Rb₃LnCl₆ · 2 H₂O (Ln = La? Nd): Preparation, Crystal Structure, and Thermal Behaviour The compounds Rb₃LnCl₆ · 2 H₂O (Ln = La? Nd) were prepared from acetic acid as powders. The preparation from aqueous solutions does not yield the pure products because RbCl precipitates as first compound. The structure of Rb₃LaCl₆ · 2 H₂O was determined by X-ray analysis of a single crystal obtained from aqueous solution. The compounds with Ln = La? Nd are isotypic. They crystallize hexagonally in the space group P6₃/m (Rb₃LaCl₆ · 2 H₂O: a = 1 220.4(2) pm, c = 1 688.6(3) (pm) with Z = 6. Anionic trimeric units [Ln₃Cl₁₂(H₂O)₆]^3? are stacked along the c-axis over the corners of the unit cell. In the stacking frequency the units are rotated by 60° with respect to each other around the c-axis. The coordination number (C. N.) of Ln³⁺ is 8, which is satisfied by four bridging and two terminal chloride ions and two water molecules. The coordination spheres of the three rubidium ions in the different atomic positions are composed differently, their C.N. are 9, 8(+1) and 6(+6). The thermal dehydration of the compounds occurs in one step. The hydrates decompose at ca. 100°C to form the anhydrous compounds Rb₂LnCl₅ und RbCl since the anhydrous chlorides Rb₃LnCl₆ are thermodynamically stable above ca. 400°C only.     

Hydrate des Cer(III)-chlorids

Hydrates of Cerium(III) Chloride The thermal dehydration of CeCl₃ · 7 H₂O to CeCl₃ gives four definite intermediates: CeCl₃ · 6 H₂O, CeCl₃ · 3 H₂O, CeCl₃ · 2 H₂O, CeCl₃ · H₂O. In the hexahydrate monomeric [CeCl₂(H₂O)₆]⁺ units exist. A structure analysis of CeCl₃ · 3 H₂O gave an orthorhombic unit cell (S.G. Pnma; Z = 4) with a = 1 242.7(4) pm; b = 881.8(8) pm, c = 693.4(5) pm. The structure consists of [CeCl_4/2Cl(H₂O)₃] chains, where two Ce³⁺ ions are connected via two chloride ions, forming bent chains in the [010] direction. The trihydrates LnCl₃ · 3 H₂O (Ln = Pr? Tb) are isotypic, also one modification of LaCl₃ · 3 H₂O. The structures of the di- and mono-hydrate are not yet known. Molar volumina and solution enthalpies in water vary linearly with the number of H₂O molecules per formula unit.