G. Heublein

DONATOR ACCEPTOR BEHAVIOR OF AEROSIL IN SEVERAL ORGANIC LIQUIDS

Aerosil is studied with regards to its acceptor behavior by means of electrokinetic measurements and UV measurements in various organic liquids. Whereas the values of the general negativ zeta-potential only approximately correspond with the donor number of the liquids determined according to Gutmann, Marie and Gal, and Kravtzov et al., an excellent agreement between zeta-potential and the UV maximum of a dicyano-bis(1,10-phenanthrolin)-ferric [Fe(phen)2(CN)2] complex adsorbed at the solid-liquid interface was found. The fact that traces of water decrease the negative zeta-potential of aearosil in organic liquids is attributed to hydration of the aerosil surface.

Halbempirische berechnung der konformationsenergien von halogenäthanen

Zusammenfassung Mit Hilfe der halbempirischen Potentialfunktionsansatze nach Buckingham und nach Lennard-Jones werden die Potentialbarrieren und die Energiedilferenzen moglicher Konformationen von 26 halogensubstituierten Athanen berechnet. Es erfolgt em Vergleich mit experimentell bestimmten Werten.

Konformationsanalyse von erythro-1,2-diphenyläthanderivaten

Zusammenfassung Die Konformationsgleichgewichte von neun substituierten 1,2-Diphenylathanderivaten wurden mit Hilfe der H 1 -NMR-Spektren und der Dipolmoment-Messung ermittelt. Die Temperaturabhfingigkeit der Kopplungskonstanten erlaubt Aussagen uber die relative Stabilitat der Konformationen.

Synthesis and characterization of stationary phases on the basis of silicas modified with epoxidized polybutadienes. IV: Chromatographic experiments on a new amino-functionalized stationary phase for high-performance liquid chromatography

Abstract Amino-functionalized stationary phases derived from polybutadiene epoxide-coated silica possess a good stability in aqueous buffer solutions at different pH. Pressure stability of the highly polymer-loaded support, separation of carbohydrates, purines and pyrimidines, and the influence of the pH of the eluent mixture on the retention behaviour of ionisable samples, such as substituted benzoic acids, are demonstrated.

Selective Polymerization from Olefin Mixtures

Abstract For inorganic as well as for organic reactions the necessary raw materials in general are mixtures of different components. Different separation processes are needed before proceeding to the reactions resulting in the wished for transformation product. The development of new chemical procedures for obtaining energy or raw materials and their use without getting by-products or products without economical profit require new methods in chemical research.

Halbempirische berechnung der konformationsenergien von dihalogenbutan- und dihalogenhexanverbindungen

Zusammenfassung Auf der Grundlage halbempirischer Potentialfunktionsansatze werden die Energiedifferenzen moglicher Konformationen fur vicinale 2,3-Dihalogenbuta berechnet. Die relativen Konformationsstabilitaten werden diskutiert.

Cationic Polymerization in the Presence of π-Electron Acceptors

Abstract The cationic polymerization of various vinyl and cyclic monomers was studied in the presence of strong electron acceptors (EA) such as tetracyanoethylene, chloranil, and syn-trinitrobenzene, added in quantities commensurate with the initiator concentrations. In all cases studied, the presence of EA brings about an increase both in the overall polymerization rate and in the molecular weights of the polymers obtained without changing the kinetic scheme of the reaction. The EA added also affects the monomer reactivities in the copolymerization reaction, the insertion of less reactive monomer being favored. The effect of EA was explained in terms of complexation with the counter-ion which causes a shift of the ionic equilibrium in the system.

Stereochemische untersuchungen an substituierten vicinalen dihalogenäthanen

Zusammenfassung Aus den IR- und Raman-Spektren werden die konformationsabhangigen CCl- und CBr-Schwingungen von substituierten vicinalen Dihalogenalkanen bestimmt und Hinweise auf die Konformerenverteilung erhalten.

Direkter nachweis der ionaren zwischenstufe bei der elektrophilen bromaddition an olefine

Zusammenfassung Fur die elektrophile Bromaddition an Olefine konnten mit Hilfe der Hochfrequenztitration Leitfahigkeitseffekte in polaren Losungsmitteln und Losungsmittelgemischen nachgewiesen werden. Die Grosse der Leitwertanderungen zeigt eine Abhangigkeit vom Solvatationsvermogen der einzelnen Losungsmittel. Die Ergebnisse charakterisieren den Zwischenzustand der Reaktion als ein Gleichgewicht zwischen inneren Ionenpaaren und getrennt solvatisierten Ionen.

Cationic Interracial Polymerization of p-Methoxystyrene by Means of Triphenylmethylium Halide-Aerosil Initiation

Abstract Cationic polymerizations of p-methoxystyrene initiated by triphenylmethylium halides in conjunction with silica surfaces proceed via ion pair intermediates. The polymerization yields both aerosil-polymer composites and soluble polymers. The triphenylmethylium halides are active only on the surface of the solid, which is demonstrated by means of adsorption and zeta-potential measurements in 1,2-dichloroethane. The influence of the overall monomer concentration and initiator concentration on the MWD curves and composite formation is discussed in relation to the mechanism of cationic polymerization. Triphenylmethylium bromide-aerosil adsorbates yield soluble polymers with narrow MWD curves (M w/M n ≃ 1,2). This behavior approaches living conditions. The formation of composites mainly proceeds in the Stern layer of the ion pair layer which covers the aerosil particle while the generation of soluble polymers occurs in the diffuse layer. The behavior of interfacial polymerization is discussed in relati...