Zirconocene-mediated route to enantiopure 9-oxabicyclononanes functionalized on both carbon bridges

[reaction: see text] A zirconocene-mediated ring contraction of 4-vinylfuranosides generated either from d-arabinose or d-glucose is followed by sequential oxidation to the ketone and alkynyl Grignard addition. The resulting cis-cyclobutanediols are subjected in turn to thermal rearrangement and intramolecular oxymercuration-demercuration. The regiochemistry of the final ring closure is controlled by the nature of R.     

A mass spectral study of some symmetric and unsymmetric sulfides,disulfanes, and trisulfanes

The low-resolution mass spectra of 13 trifluoromethyl and/or methyl sulfur-containing compounds (CF₃S_nCF₃, CF₃S_nCH₃, CH₃S_nCH₃, CF₃S_mCl, and CH₃S_mCl; n = 1, 2, 3; m = 1, 2) are reported and discussed. There is a considerable similarity between the fragmentation pattern of compounds with the same terminal groups. However, with a fluorinated and a non-fluorinated methyl group, the major fragmentation products produced are similar to those for the dimethyl compounds.     

An ab-initio study of the molecular structure and properties of HPO

An ab-initio gaussian lobe function study of the structure and some molecular properties of the HPO molecule is reported. By a partial optimization of the geometrical structure the following equilibrium structure parameters are found: r_PO = 1.536 Å; r_PH = 1.475 Å; the bond angle is found to be close to 102° with a bending force constant of 0.58 mdyne/Å. The dipole moment, effective charges and quadrupole term components at various bond angles are reported. The wavefunction of the equilibrium geometry is available from the authors upon request.     

The key elements of traceability in chemical measurement: agreed or still under debate?

Talking about "traceability" means talking about a "property of the result of a measurement", about "the value of a standard", about "stated references" and about an "unbroken chain of comparisons". It describes by which comparison, and to which other value, the result of a measurement has been obtained, i.e. is "traceable to". It is about the underlying structure of the measurement process of the result of a measurement and therefore about the authority of the result. Since values carried by (certified) reference materials have also been obtained by measurement, the definition of traceability equally applies. Traceability in the context of reference materials is also about the authority of the values carried by the (certified) reference materials and is, therefore, of key importance for the authority of the reference materials themselves. Hence, values of results of measurements constitute part of the traceability chain and their uncertainties are an intrinsic accompanying phenomenon. Uncertainties need a traceability chain against which they can be evaluated, and a traceability chain is an a priori requirement for evaluating the uncertainty budget of a measurement result. An attempt has been made to exemplify "traceability" chains in some types of chemical measurement and to identify the degree of international agreement on the key elements of "traceability". It is concluded that there is less than universal agreement on this issue. The debate should continue in order to arrive at the international understanding and agreement needed, as "traceability" is now being incorporated in the International Organization for Standardization (ISO), the International Laboratory Accreditation Co-operation (ILAC) and in other "guiding" or regulatory documents. It is also the reason why the Institute for Reference Materials and Measurements (IRMM) has taken up the study of the concept in its core programme on Metrology in Chemistry, and why it sponsored the Workshop in Bratislava.     

Etude de la structure de l'iodatochromate de potassium par spectrographie d'absorption infrarouge entre 3 et 35μ

Résumé Dans le spectre d'absorption infrarouge de l'iodatochromate de potassium K[(CrO₃)(IO₃)], on peut identifier la présence de bandes de vibration de valence de ponts Cr-0-I à 508 et680 cm^–1.

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Summary The infrared absorption spectrum of potassium iodatochromate K(CrO₃)(IO₃) contains vibration bands of the valence bridges Cr-O-I at 508 and 680 cm^–1.

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Zusammenfassung Im Infrarot-Absorptionsspektrum des Kaliumjodatochromats lassen sich Banden der Valenzschwingungen der Atomgruppe Or-O-J bei 508 und 680 cm^–1 nachweisen.

     

A theorem on asymptotic expansion of Feynman amplitudes

For any Feynman amplitude, where any subset of invariants and/or squared masses is scaled by a real parameter going to zero or infinity, the existence of an expansion in powers of and ln is proved, and a method is given for determining such an expansion. This is shown quite generally in euclidean metric, whatever the external momenta (exceptional or not) and the internal masses (vanishing or not) may be, and for some simple cases in minkowskian metric, assuming only finiteness of the — eventually renormalized — amplitude before scaling. The method uses what is called Multiple Mellin representation, the validity of which is related to a generalized power-counting theorem.On leave of absence from University of Bahia (Brazil). Fellow of CAPES, Brazil     

Réactions de germylènes avec divers oxirannes et le thiiranne. Mise en évidence de germanones et germathiones intermédiaires. Communication préliminaire

Complexed dialkylgermylenes R₂GeNR₃ or R₂GePy react with oxiranes or thiirane and lead to dialkylgermanone and germathione via germaoxetanes or germathiacyclobutane. The formation of germadioxolanes or germadithiolane finally observed arises from condensation of dialkylgermanone (or germathione) on oxiranes (or thiirane).     

Coordination properties of a diarylaza crown ether appended with a luminescent [Ru(bipy)3]2+ unit

The [Ru(bipy)(2)(1)](PF(6))(2) (bipy refers to 2,2'-bipyridine) complex, comprising a ruthenium(II) tris(2,2'-bipyridine) luminophore covalently linked to a di[(o-triethyleneglycoxy)phenyl]amine crown ether 1, has been synthesized and fully characterized. The photophysical properties of this metal complex have been examined in solution at ambient temperature. Luminescence from the metal complex is enhanced significantly in the presence of various adventitious cations, including protons. In particular, Li(+) cations bind to the crown ether, as evidenced by (1)H NMR and luminescence spectroscopy. Cation binding serves to decrease the rate of reductive quenching of the triplet state of the metal complex, thereby increasing the extent of luminescence. The solution-phase conformation of [Ru(bipy)(2)(1)](PF(6))(2), with and without encapsulated Li(+), has been examined by 2-D NMR and by molecular dynamics simulations.     

The preparation of precisely defined lithium isotope mixtures

The need for accurate (< 0.06%) isotopic blends of ⁶Liand ⁷Li is explained and their preparation is discussed. It is shown that lithium must be determined at an accuracy level better than 0.035%. Four methods — acid-base titration with hydrochloric acid or benzoic acid, and weighing as sulphate or carbonate — were tested and improved for the precise and accurate analysis of lithium hydroxide solutions. The results of these four methods for a 0.1 M solution agreed within ± 0.02%. The preparation of pure isotopically enriched lithium hydroxide solutions, with specially purified cation- and anion-exchangers, is described. The prepared products contain as little as 100 μg of other alkali metals and 50 μg of alkaline-earth metals per gram of lithium, and are sufficiently free of anions to permit accurate chemical assay of lithium. No changes in the isotopic compositions of 99% ⁶Li or 99.99% ⁷Li were detected during the treatment.     

Analytical study of highly condensed non ionic surfactants. Separation on cation exchangers

Summary This study was aimed at optimizing the separation of non-ionic surfactants, resulting from the condensation of ethylene oxide with natural fatty alcohols in the C₁₆ and C₁₈ range (saturated and unsaturated), and presenting a high degree of condensation, i.e. 20 and 25 ethylene oxide units (Brij 99 and KM 25). The cation exchange stationary phase is a partially ionized silica, conditioned in different ways. We have studied the influence of the nature of cations on the separation selectivity. Cations studied included alkali metals (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺), alkaline earth metals (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), transition metals (Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Cu²⁺), and quaternary ammonium (NH ₄ ⁺ , NMe ₄ ⁺ ) ions as well as a proton (acetic acid). The influences of ionic strength, pH and addition of cosolvent were examined. A study of the influence of temperature on the system selectivity evidenced a strong interdependance of these two parameters. The optimized conditions [mobile phase: CH₃CN/H₂O (92/8), pH 7.4, sodium acetate 5.10^–3 M; temperature gradient between 25 and 50°C] allowed for the first time the distributions of Brij 99 and KM 25 to be obtained.