Kautschuk

Ohne Zusammenfassung     

Zur Untersuchung von Drogen und daraus dargestellten Pr?paraten

Ohne Zusammenfassung     

Ueber die Depolymerisation und Umwandlung des Kautschuks

Ohne ZusammenfassungVorgetragen beim 8. internationalen Kongreß für angewandte Chemie.Uebersetzt von H. Brehm (Dresden).     

Laboratoriumspraxis

Ohne Zusammenfassung     

Detection of negative ions in glow discharge mass spectrometry for analysis of solid specimens

A new method is presented for elemental and molecular analysis of halogen-containing samples by glow discharge time-of-flight mass spectrometry, consisting of detection of negative ions from a pulsed RF glow discharge in argon. Analyte signals are mainly extracted from the afterglow regime of the discharge, where the cross section for electron attachment increases. The formation of negative ions from sputtering of metals and metal oxides is compared with that for positive ions. It is shown that the negative ion signals of F^? and TaO₂F^? are enhanced relative to positive ion signals and can be used to study the distribution of a tantalum fluoride layer within the anodized tantala layer. Further, comparison is made with data obtained using glow-discharge optical emission spectroscopy, where elemental fluorine can only be detected using a neon plasma. The ionization mechanisms responsible for the formation of negative ions in glow discharge time-of-flight mass spectrometry are briefly discussed.     

Exploring Diradical Chemistry: A Carbon‐Centered Radical May Act as either an Anion or Electrophile through an Orbital Isomer

Diradical intermediates, formed by thermolysis of alkynylcyclobutenones, can display radical, anion, or electrophilic character because of the existence of an orbital isomer with zwitterionic and cyclohexatrienone character. Our realization that water, alcohols, and certain substituents can induce the switch provides new opportunities in synthesis. For example, it can be used to shut down radical pathways and to give access to aryl carbonates and tetrasubstituted quinones.     

A convergent regiospecific synthesis of zirconium enolates

α-Lithiated phenylsulphonyloxiranes insert into alkenylzirconocene chlorides with loss of phenylsulphinate to give zirconyloxiranes which smoothly rearrange by either α- or β- C-O cleavage to afford regiodefined zirconium enolates which may be further elaborated.