ÜBER STERISCH SPERRIGE ORGANOPHOSPHORVERBINDUNGEN: ISOPROPYL-SUBSTITUIERTE THIOPHOSPHORYLBROMIDE

Abstract

Durch selektive Grignardierungsreaktionen werden Verbindungen des Typs R(i-C₃H₇)PBr erhalten und in R(i-C₃H₇)P(S)Br überführt. Die chemische Verschiebung δ p in RR'P(S)Br (R,R' = CH₃, C₂H₅, i-C₃H₇, t-C₄H₉) wächst linear mit der Zahl der ß-ständigen Methylgruppen in R und R'. AB₃C₃X-Spektren der i-C₃H₇P-Struktur-elemente werden berechnet.

Selective Grignard-type reactions lead to R(i-C₃H₇)PBr which are converted to R(i-C₃H₇)P(S)Br. Chemical shift values δ p in RR'P(S)Br (R,R' = CH₃, C₂H₅, i-C₃H₇, t-C₄H₉) increase linearly with the number of ß-methyl groups in R and R'. AB₃C₃X-spectra are calculated for i-C₃H₇P-moieties.     

Synthese und Kristallstrukturen von (PPh4)2[TeS3] · 2 CH3CN und (PPh4)2[Te(S5)2]

Synthesis and Crystal Structures of (PPh₄)₂[TeS₃] · 2 CH₃CN and (PPh₄)₂[Te(S₅)₂] (PPh₄)₂[TeS₃] · 2 CH₃CN was obtained by the reaction of PPh₄Cl, Na₂S₄ and Te in acetonitrile. With sulfur it reacts yielding (PPh₄)₂[Te(S₅)₂]. The crystal structures of both products were determined by X-ray diffraction. (PPh₄)₂[TeS₃] · 2 CH₃CN: triclinic, space group P1 , Z = 2, R = 0.041 for 4 629 reflexions; it contains trigonal-pyramidal [TeS₃]^2? ions with an average Te? S bond length of 233 pm. (PPh₃)₂[Te(S₅)₂]: monoclinic, P2₁/n, Z = 2, R = 0.037 for 2 341 reflexions. In the [Te(S₅)₂]^2? ion the tellurium atom has a nearly square coordination by four S atoms. Along with the Te atoms each of the two S₅ groups forms a ring with chair conformation.     

Stereochemical analysis of constituents of essential oils and flavor compounds by enantioselective capillary gas chromatography

Modified cyclodextrins interact enantioselectively with a great variety of volatile chiral constituents of essential oils by forming diastereomeric inclusion complexes. Capillary gas chromatography is used for resolving the enantiomers of terpenoid hydrocarbons (camphene, α-pinene, limonene, α-phellandrene), carbonyl compounds (carvone, fenchone, menthone, isomenthone, piperitone, camphor, myrtenal), and alcohols (trifluoroacetylated β-citronellol, myrtenol, trans-pinocarveol, 1-octen-3-ol, and underivatized linalool). The enantiomeric composition of some of these compounds in a variety of essential oils is investigated.     

A Cautionary Note on Likelihood Ratio Tests in Mixture Models

We show that iterative methods for maximizing the likelihood in a mixture of exponentials model depend strongly on their particular implementation. Different starting strategies and stopping rules yield completely different estimators of the parameters. This is demonstrated for the likelihood ratio test of homogeneity against two-component exponential mixtures, when the test statistic is calculated by the EM algorithm.     

On the effect of cell irregularity on the effective behavior of solid foams

The present study provides an analytical probabilistic approach for the homogenization of hyperelastic solid foams with irregular microstructure. The scheme is based on the multiple analysis of a randomized representative volume element in conjunction with a stochastic evaluation of the results in terms of the stress mean values and the corresponding standard deviations defining the scatter band widths. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Finitary Treatment of Operator Controlled Derivations

By combining the methods of two former papers of ours ([6] and [7]) we develop a finitary ordinal analysis of the axiom system KPi of Kripke‐P atek set theory with an inaccessible universe. As a main result we obtain an upper bound (in the fast‐growing hierarchy) for the provably recursive functions of KPi.     

Molecular Weight Influence on Gelatin Gels: Structure,Enthalpy and Rheology

Summary: This paper deals with the gelation properties of gelatins with various molecular weights. The samples are 4 different extracts from limed bones. We investigated firstly the structural properties: the helix amounts by optical rotation measurements and the enthalpy of helix formation and melting, with the same thermal protocols and for various concentrations. Comparison between the two methods allowed deriving the enthalpy of helix-coil transition and melting. Rheology was performed under the same conditions with a stress controlled rheometer working with a fixed, very small, strain during gel formation, maturation and melting. Correlation between all the measurements confirms the existence of the master curve for storage modulus versus gelatin concentration for all samples investigated.