Remarkable selectivity in addition of alcohols to epoxydienes of 5,7 bicyclic and 5,7,6 tricyclic systems

Acid-catalyzed addition of alcohols to tricyclic dienyl epoxides such as 4 or bicyclic vinyl oxiranes such as 17 exclusively occurred at the vinyl terminus of unsaturated system through a typical S(N)2' process affording 1,6- and 1,4-dioxygenated derivatives, respectively.     

Role du methyle 4β dans la formation des oxetanones en serie steroïde. Cas du cycle B.

The formation of oxetanones $\text{5}$ from bromoketonee $\text{2}$ requires the presence of a β-methyl group at C-4. The yield of the reaction $\text{2}$→$\text{5}$ is improved by addition of water to the medium.     

Catalysts for methane transformation in the absence of oxygen, II. Nature of active centers

The activity of supported manganese oxide catalysts doped with copper, chromium and iron oxides in methane to higher hydrocarbons transformation in non-oxidizing atmosphere has been studied. Chromium and iron oxides are more effective promoters than copper oxide. Redox centers of dehydrogenation ability are active in methane transformations.     

EAL interlaboratory comparison Wa1 – Testing of potable water

 The accreditation of laboratories has emphasized the use of interlaboratory comparisons as a tool to monitor the comparability and accuracy of results laboratories produce. An interlaboratory comparison for water laboratories was organized among European Cooperation for Accreditation (EA) member countries; 30 laboratories, 7 of which were not accredited, from 14 European countries participated in this intercomparison. All the laboratories were chosen by the appropriate national accreditation bodies, with the instruction to select as participants those laboratories which act as national reference laboratories in this field. About 90% of the data collected was considered satisfactory after statistical treatment. Non-accredited laboratories performed as well as accredited laboratories. The laboratories were asked to take corrective action and report the corrections to the accreditation bodies. A great variation in the reported uncertainties of the results was observed. There seems to be a need to organize EA interlaboratory comparisons for national reference laboratories analysing water. It is obvious that even reference laboratories need training in how to estimate the uncertainty of results. Received: 22 July 1998 · Accepted: 21 September 1998     

A videomicroscopic study of the effect of l-cis-diltiazem on the photobehavior of Stentor coeruleus

The protozoan ciliate Stentor coeruleus displays a step-up photophobic response to an increase in light intensity in its environment. The motile response consists of a delayed stop of ciliary beating and transient ciliary reversal period. Such light-avoiding behavior was significantly influenced by an incubation of cells with l-cis-diltiazem, a common blocker of cyclic guanosine monophosphate (cGMP)-gated ion channel conductance. The introduction of l-cis-diltiazem to the medium induced ciliary reversal in control cells, mimicking the step-up photophobic response. In light-stimulated ciliates, the presence of this inhibitor caused a substantial decrease of the latency of ciliary stop response, prolongation of the ciliary reversal duration and also an increase of cell photoresponsiveness in a dose- and time-dependent manner. The obtained behavioral results support the suggestion that the photosensitive ciliate S. coeruleus possesses cGMP-gated channels, which may be involved in the process of light signal transduction for the motile photophobic response.     

ORTHO-selective phenol methylation over iron-magnesium oxide catalysts

Alkylation of phenol to ORTHO-cresol and 2,6-xylenol with methanol in the presence of iron and iron-magnesium oxide catalysts was investigated. The catalysts displayed high activity and stability. Addition of magnesium oxide to the iron catalyst increases its selectivity towards C-alkylation in ortho-position. It was found that the active phase in the investigated catalysts is highly dispersed magnetite or mixed spinel of Fe(MgFe)O₄ type. It is noticed that if Fe⁺² ions are replaced by Mg⁺² ions in the spinel the basicity of the bifunctional catalyst is augmented, increasing ortho-selectivity of alkylation.     

Circular dichroism of olefins—IV: A semiquantitative prediction of the intensity of the cotton effect of allyl alcohols and ethers

A semi quantitative prediction of the intensity of the Cotton effect of a few allyl alcohols and ethers in the steroid and diterpene series has been derived. It relies on a calculation of the weight of the various conformations and on the allylic bond polarization model.     

Determination of the enantiomeric composition of carprofen by proton nuclear magnetic resonance spectroscopy with a chiral lanthanide-shift reagent

The enantiomeric composition of carprofen has been determined in a rapid and reliable manner by proton nuclear magnetic resonance spectroscopy with a chiral lanthanide-shift chelate. Carprofen was converted into a mixture of enantiomeric methyl ester derivatives which were then complexed with tris[3-(heptafluoropropylhydroxymethylene)-(+)-camphorato]europium(III) in CDCl(3). The concentration of substrate in the test sample was 0.15M and the chiral-shift reagent:substrate molar ratio was 0.453. Determination of the enantiomers was based on the relative intensities of the signals for the alpha-methyl protons. The mean recovery +/-SD for six determinations of S(+)-carprofen from synthetic enantiomeric mixtures was 99.3 +/- 1.7%.     

Autoassociates and tautomerism of 2-oxo-5-halogenopyrimidines: theoretical and experimental investigations

Theoretical calculations (on a semi-empirical level) of energy and geometry of the autoassociates of two tautomeric forms of 2-oxo-5X-pyrimidines (X = H, Cl, Br) are presented. On the basis of the calculated energies of autoassociates it is possible to explain the enol—keto tautomeric transition between the gas phase and condensed phases. We propose a double-proton transfer reaction as a possible mechanism for the tautomeric transition.

Infrared absorption spectra of 2-oxo-5X-pyrimidines in the v(NH …) and v(C=O) regions in solid phases and in low-temperature argon matrices are also presented and discussed. Comparison of IR spectra and results of the theoretical calculations with known crystallographic structures of 2-oxo-5X-pyrimidines (X = H, F, Cl) lead to the conclusion that the crystal structure of the 5-bromo derivative should be similar to that of the 5-chloro derivative.     

Ca5Sn2As6, das erste Inoarsenidostannat(IV)

Ca₅Sn₂As₆, The First Inoarsenidostannate(IV) The new compound Ca₅Sn₂As₆ crystallizes in the orthorhombic system (space group Pbam (No. 55)) with the lattice constants s. ?Inhaltsübersicht”?. In the structure SnAs₄-tetrahedra are connected by common corners to ?Einereinfach”? chains. The compound belongs to the “Zintlphases”.