Ethylenic compounds reactivity: bromination—XLI: Relative reactivities of R1CMeCH2 and R1CHCMe2 series as a criterion for distinguishing between bridged and acyclic transition states. Degree of symmetry of the bromonium ion-like transition state

Reactivities of homogeneous series of ethylenic compounds R¹CHCH₂1, trans R¹CHCHMe 2, R¹MeCCH₂3 and R¹CHCMe₂4 have been measured in methanol at 25°C (R¹ Me, Et, n-Pr, -CH₂C₆H₅-CH₂OCOCH₃, -CH₂Cl). The criterion developed to decide between a bridged and a carbonium ion-like transition state is based on an internal comparison of the series and avoids resorting to external structural scales. Even in the case of alkenes 3 and 4 which are very dissymmetric with respect to polarity, the sensitivity to polar effects remains constant and the transition state behaves like a symmetric entity; only a slight secondary effect, attributed to hyperconjugation, is detectable.     

Improvement of the HPLC analysis of anthocyanins in red wines by use of recently developed columns

Comparison of the separation performance of five newly developed pH-stable HPLC columns is described for the analysis of anthocyanins in red wines. Separation of twenty anthocyanins in a single run is described using the most appropriate method.     

Schnelle Trennung von Rückstoßprodukten in der Gasphase

Experiments are described in which recoil products are separated fast and selectively. The aim of these investigations is an identification of short-lived nuclides, either for the study of nuclear reactions or for the study of decay properties of new products. The recoil products were provided by a Cf-252 source. The transportation zone and the identification zone could be heated to different temperatures. Using N₂ as carrier gas it was possible to separate Te selectively under certain experimental conditions. When Cl₂ was added, Sb, Tc, Nb, Mo, Zr, Ru and Sn were transported. Transport output was determined in dependence of temperature and composition of the gas.     

Der Verlauf der Umlagerung von Phenacylsulfenylmorpholid zu Phenylglyoxylsäurethionmorpholid in Gegenwart von Schwefel

Zusammenfassung Bei der Einwirkung von elementarem Schwefel auf Phenacyl-sulfenylmorpholid entsteht unter H₂S-Abspaltung Phenylglyoxyl-säurethionmorpholid. Durch Einsatz von radioaktivem Schwefel wurde festgestellt, daß diese Umlagerungsreaktion über die Stufe einergem. Dimercaptoverbindung verläuft.

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Reaction of elementary sulfur with phenacylsulfenylmorpholide gives phenylglyoxylic acid thionmorpholide while hydrogen sulfide is eliminated. The rearrangement proceeds, as was shown by use of radioactive sulfur, via agem. dimercaptocompound as intermediate.

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47. Mitt.:F. Asinger, W. Schäfer undA. Saus, Mh. Chem.96, 1265 (1965).

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Teil der DissertationA. Saus, Techn. Hochsch. Aachen, 1964.     

Free-electron attachment to coronene and corannulene in the gas phase

Electron attachment to the polyaromatic hydrocarbons coronene and corannulene is studied in the electron energy range of about 0-14 eV using a high-resolution crossed electron-neutral beam setup. The major anions observed are the parent anions peaking at about 0 eV with cross sections of 3.8 x 10(-20) and 1 x 10(-19) m(2), respectively. The only fragment anions formed in coronene and corannulene are the dehydrogenated coronene and corannulene anions. Other anions observed in the negative mass spectra at about 0 eV can be ascribed to impurities of the sample. High-level quantum-mechanical studies are carried out for the determination of electron affinities, hydrogen binding energies, and structures of both molecules. The behavior of coronene and corannulene upon electron attachment is compared with that of other polyaromatic hydrocarbons studied previously.     

Electrochemical formation and clevage of bis-imidazolyls

Bis-(2,4,5-triphenylimidazolyls) result from the dimerization of 2,4,5-triphenylimidazolyls and from the nucleophilic attack of 2,4,5-triphenylimidazole anions upon 2,4,5-triphenylimidazolylium cations. The isomeric bis-imidazolyls consist of imidazole and isoimidazole systems. Imidazoles undergo only anodic oxidation, isoimidazoles only cathodic reduction. Therefore the bis-imidazolyls may be analyzed from their electrochemical behaviour. Bis-(2,4,5-triphenylimidazolyl)-1,2′ and bis-(2,4,5-triphenylimidazolyl)-1,4′ undergo reductive bond cleavage in an ē.c?.ē. mechanism from which 2,4,5-triphenyl-imidazole anions result. The electrochemical properties of one of the bis-imidazolyls agree with that of 1,4,5-triphenyl-2-(2,4,5-triphenylisoimidazolyl-4)-imidazole and not with that of bis-(2,4,5-triphenylimidazolyl)-2,4′ as reported in literature.     

Additivity of inelastic gamma ray scattering in methanol—water and ethanol—water solutions

Compton profiles of water, methanol, ethanol and mixtures of methanol—water and ethanol—water have been measured using 60 keV gamma rays from a 5 Ci annular²⁴¹ Am source. The profile of each mixture has been compared with the profile of the sum of the components and at all concentrations a linear behaviour has been found.     

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Book reviews

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Notices bibliographiques

     

Scanning Kelvin Microscope: a new method for surface investigations

Based on the well known Kelvin probe for work function measurements a new microstructure analysis system - the Scanning Kelvin Microscope - has been developed. It allows to measure simultaneously with high lateral resolution the distribution of the contact potential difference (CPD) between a conductive sample and a reference probe together with the topographical structure of the sample surface. The measurement is contact free and non-destructive and can be carried out in natural environments. At present the lateral resolution of the measurement approaches 5 microm. The results can be displayed on a computer in three dimensional colour pictures.