Cs2(H3O)Pr(CH3COO)6 und Cs2Pr(CH3COO)5: Synthese,Kristallstrukturen und Thermolyse. Über die analogen Acetate mit Lanthan bis Terbium

Cs₂(H₃O)Pr(CH₃COO)₆ and Cs₂Pr(CH₃COO)₅: Synthesis, Crystal Structures and Thermolysis. Analogous Acetates with Lanthanum through Terbium Single crystals of Cs₂(H₃O)Pr(CH₃COO)₆ are obtained as green plates from an acetic acid solution (≈50%) of Cs₂CO₃ and Pr(CH₃COO)₃ · 1,5 H₂O. The crystal structure monoclinic, Cm, Z = 2, a = 1 540.4(4), b = 691.3(2), c = 1 221.5(4) pm, β = 104.60(5)°, V_m = 379.1(2) cm³/mol, R = 0.040, R_w = 0.035 was determined from four-circle-diffractometer data. The structure consists of monomeric Pr(CH₃COO)₃ units, in which Pr³⁺ is surrounded by nine oxygen atoms. These monomers are linked together to infinite layers parallel (001) by common acetate oxygen atoms with two ?molecules”? of Cs(CH₃COO). Together with an additional acetate ion coordinated to one of the Cs⁺ ions the composition of the layers is [Cs₂Pr(CH₃COO)₆]^?. Between these layers H₃O⁺ is located for electroneutrality. Thermal decomposition of Cs₂(H₃O)Pr(CH₃COO)₆ was examined with thermoanalytical methods (TG/DTA with coupled gas analysis), Guinier-Simon technique and IR spectroscopy: beginning at 70°C the compound looses water and acetic acid. It decomposes topotactically to Cs₂Pr(CH₃COO)₅. At 270°C this acetate decomposes to Cs₂CO₃ and Pr₂O₂CO₃ which emits CO₂ at 600°C form ing Pr₂O₃or PrO_2?x Single crystals of Cs₂Pr(CH₃COO)₅ were obtained from Pr(CH₃COO)₃, in molten Cs(CH₃COO) at about 200°C. The crystal structure tetragonal, P4₃, Z = 4, a = 1 174,5(2), c = 1 480,5(3) pm, V_m = pin,307,5(1) cm³/mol, R = 0,061, R_w= 0,031 again consists of Pr(CH₃COO)₃, monomers where Pr³⁺ has 9 oxygen ligands in its first coordination sphere. They are linked together by two ”molecules“ of cesium acetate to infinite chains along [00l] around the 4, screw axis. There are also acetate bridges between these chains. Isotypic compounds Cs₂(H₃O)M(CH₃COO)₆ and Cs₂M(CH₃COO)₅, and Cs₂M(CH₃COO)₅with M = La? Tb, were obtained from acetic acid solutions or thermal decomposition and were characterized by X-ray Guinier techniques.     

New facts concerning the reaction of K, K(15-crown-5)2 with phenyl glycidyl ether: unexpected formation of potassium cyclopropoxide

A new mechanism of the reaction of K⁻, K⁺(15-crown-5)₂ with phenyl glycidyl ether is presented. The linear ether bond is attacked only to a small extent, if at all. As the main reaction path the oxirane bond in the β-position is cleaved, followed by the γ-elimination of potassium phenoxide and the formation of potassium cyclopropoxide. Crown ether ring opening also occurs in reactions with organometallic intermediates.     

Markovnikov's Rule in History and Pedagogy

In 1870–75 Markovnikov enunciatedan empirical Rule which generalized theregiochemical outcome of addition reactions tounsymmetrical alkenes. This Rule remaineduseful for about 75 years, until suchreactions came to be better understood inmechanistic terms. Thereafter the Rule couldbe deduced from principles of relativecarbocation stabilization and ceased to servean independent purpose. Nevertheless, mostorganic textbooks continue to cite it (oftenin a historically inaccurate, anachronisticway), thereby distracting student attentionfrom the underlying principles. This paperadvocates doing away with the Rule in organicchemistry textbooks and classrooms.     

Unges?ttigte Polyester und Polyester-Kautschuk-Copolymerisate durch Olefin-Metathese

Ohne Zusammenfassung     

Characters of wreath products and some applications to representation theory and combinatorics

The salient point arising out of a consideration of some seemingly independent topics in representation theory, combinatorics and the theory of numerical polynomials turns out to be a result involving characters of representations of wreath products. The topics are: symmetrized inner products of representations, irreducible characters of wreath products, Frobenius' formula for the irreducible ordinary characters of symmetric groups, the Pólya-Redfield theory of enumeration under group action in combinatorics and results of Rudvalis and Snapper that certain polynomials arising from generalized cycleindices of permutation groups are numerical.     

Zur Theorie der diffusen Reflexion und Transmission beim Vorliegen elastischer Vielfachstreuung

In order to determine the diffuse reflectivity and transmittivity of multiply scattered particles, there is not necessarily the need of solving the complete differentiointegral equation of multiple scattering. It can be shown that the problem reduces to solving a set of two simultaneous differential equations of the first order, provided that the amount of sideward scattering may be neglected. The solutions of these equations furnish all data required, if the mechanism of single scattering is known.