Dialkylzinc-assisted alkynylation of nitrones

[reaction: see text]. Reaction of nitrones with terminal alkynes takes place readily in the presence of a substoichiometric amount of diethylzinc in toluene, affording N-propargyl-hydroxylamines in excellent yields and purity.     

Air-dispersion measurement by second-harmonic heterodyne interferometry

Interferometers with long optical paths in air usually require knowledge and control of air dispersion. In addition, the measurements at several wavelengths and the dispersion properties of air allow errors caused by air turbulence to be compensated for. An innovative technique for air-dispersion measurement is described for long-baseline ground-based stellar interferometers. The technique combines second-harmonic interferometry and heterodyne detection to permit high-resolution measurement even for low optical powers. Experimental results show measurements of air dispersion in good agreement with the values predicted from the Edlén equation.     

Reaction of lithium dimethylcuprate with conformationally biased β-acyloxy enol esters - regio and stereocontrolled access to functionalized six-carbon chiral synthons

Alkyl 2-acyloxy α-D-erythro-hex-2-enopyranoside diesters, readily available from D-hexoses, are versatile intermediates fro the expeditious preparation of six-carbon chiral synthons containing alternating and/or consecutive C-methyl and hydroxyl groups.     

Autocorrelation d'un diffuseur depolarisant

The autocorrelation of a depolarizing diffuser illuminated successively by two linearly polarized beams of light is proportional to the cosine of the angle between the directions of polarization. The speckle pattern exhibits the same properties of correlation.     

The synthesis of a leukotriene with SRS-like activity

The synthesis and biological characteristics of an SRS-like leukotriene are described.     

A theoretical study of the difference in the behavior ofl- andd-alanine toward the two inverse forms of kaolinite

The adsorption ofl- andd-alanine on kaolinite is studied by means of the self-consistent field method, the field created by the crystal being simulated by that of 230 point charges, corresponding to two layers. The absolute structure we have adopted for kaolinite is that for whichthe ( ) trihedron is direct. Indeed, it has been shown that, owing to the nuclear weak interactions, this structure is more stable than the inverse structure. On the adopted structure, the l forms of the positive ion and of the zwitterion are more easily adsorbed than the d forms. The difference between the adsorption energies of thel andd forms are 0.14 and 0.04 kJ mol^–1 for the positive ion and the zwitterion, respectively. These differences are considerably larger than those arising from the weak interactions (ca. 10^–17 kJ mol^–1) so that the asymmetrical adsorption on kaolinite seems to be one of the causes of thel homochirality observed for the amino acids of proteins.     

Synthesis, reactivity, and ligand properties of a stable alkyl carbene

Stable tert-butyl diisopropylamino carbene is more nucleophilic but also more electrophilic than diamino carbenes; it undergoes cyclopropanation reactions and easily binds to metal fragments.     

Crystal structure of RbOsO3N: A new CsReO4-type compound

Crystals of RbOsO₃N are orthorhombic, space group Pnma, with z = 4, a = 5.571(1), b = 5.794(1), c = 13.735(3), Å. Intensities for 556 independent reflections collected on a four-circle diffractometer were used in the structure determination and the structure was refined to a final R value = 0.046 (R_w = 0.056). The structure consists of OsO₃N discrete tetrahedra linked together by 8-coordinated Rb ions. The oxygen and nitrogen atoms are distributed randomly. RbOsO₃N is the first compound belonging to the CsReO₄-type family for which the complete structure has been determined. This structure can be related to scheelite type but appreciable differences occur in tetrahedra arrangement.     

Mechanical forces acting within non-polar fluid dielectrics

We compare Kelvin's polarization theory with Helmholtz's energy method for calculating forces in non-polar fluid dielectrics and show that in general they give different results and that only Helmholtz's method stands on firm foundations. We also discuss these results in connection with experiments and conclude that further experiments are needed to clarify the situation.     

High-frequency driven capillary flows speed up the gas-liquid phase transition in zero-gravity conditions

Under weightlessness conditions, the phase transition of fluids is driven only by slow capillary flows. We investigate the effect of high-frequency vibrations to reproduce some features of gravity effects and show that such vibrations can greatly modify the phase transition kinetics. The investigation is performed in H2 near its critical point (critical temperature 33 K) where critical slowing down enables the phase transition process to be carefully studied. Gravity effects are compensated in a strong magnetic field gradient.