Gold-catalyzed direct oxidative coupling reactions of non-activated arenes

A general gold-catalyzed oxidative homo- and hetero-coupling of arenes in mild conditions is described. This reaction gives moderate to excellent yield using PhI(OAc)₂ as an oxidant. The effects of temperature, solvent, oxidant and concentration of substrate in this process have also been studied in detail. The product identity and distribution as well as the substrate limitation give us insights into this type of gold catalysts. Depending upon the reaction conditions, the gold catalyst behaves as a simple Lewis acid, which produces amines from arenes using DIAD as an aminating reagent.     

Entanglement in a periodic quench

We consider a chain of free electrons with periodically switched dimerization and study the entanglement entropy of a segment with the remainder of the system. We show that it evolves in a stepwise manner towards a value proportional to the length of the segment and displays in general slow oscillations. For particular quench periods and full dimerization an explicit solution is given. Relations to equilibrium lattice models are pointed out.     

Problems of standard qualities and standards in environmental analysis

Summary Various problems arising with standards in environmental analysis are described and discussed. Every actual analytical result is only meaningful in correlation to the standard qualities of the system in consideration. Need, purpose, evailability and use of standards are discussed and several examples are presented.

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Problematik der Standards und ihrer Qualität in der Analyse von Umweltmaterial

Zusammenfassung Die zahlreichen Probleme, die sich bei der Suche nach Standards für die Analyse von Umweltmaterial ergeben, werden aufgezeigt und diskutiert. Ein analytisches Resultat hat nur Bedeutung, wenn es in Beziehung zu den Standardqualitäten des betreffenden Systems gesehen wird. Notwendigkeit, Zweck, Verfügbarkeit und Anwendung des Standards werden erörtert und mit Beispielen erläutert.

Presented at the 6th Annual Symposium on Recent Advances in the Analytical Chemistry of Pollutants, April 21–23, 1976; Vienna, Austria.     

Transient and stationary nutations in chemically induced dynamic nuclear polarization

Transient nutations are observed in nuclear magnetic resonance during continuous generation of magnetization at and near resonance in reactions leading to chemically induced dynamic nuclear polarization. Modulation of the reaction with the nutation frequency leads to stationary nutations. The phase-sensitive detection of the nutation signals is used to discriminate effects of chemically induced polarization from steady state resonance signals. For single line spectra the effects are quantitatively explained by Bloch-type equations containing magnetization production terms. Experimental results obtained during photochemical reactions of di-tert-butyl ketone demonstrate general applications of the method.     

Ring contraction in 2,2,6,6-tetramethylpiperidin-4-one with dichlorocarbene under phase transfer conditions

The preparation of a 5-membered lactam via a postulated dichlorooxirane intermediate is described.