The Brønsted acid-catalyzed direct aza-Darzens synthesis of N-alkyl cis-aziridines

A mild protocol for the synthesis of cis-aziridines is described that employs a catalytic amount of Br?nsted acid. Despite the potential for diazo compound decomposition via alkylation or homocoupling upon exposure to a proton source, these pathways are slow relative to [2 + 1] annulation in the presence of a Schiff base, leading to aziridine product. The process uses no metals or reagents that must be removed chromatographically, exhibits rapid turnover rates, and produces only atomic nitrogen as a coproduct. High levels of relative stereocontrol are also possible when forming the Schiff base from a chiral nonracemic aldehyde.     

Dynamics of magnetic defects in heavy fermion LiV2O4 from stretched exponential 7Li NMR relaxation

7Li NMR measurements on LiV2O4 from 0.5 to 4.2 K are reported. A small concentration of magnetic defects within the structure drastically changes the nuclear magnetization relaxation versus time from a pure exponential as in pure LiV2O4 to a stretched exponential, indicating glassy behavior of the magnetic defects. The stretched exponential function is described as arising from a distribution of 7Li nuclear spin-lattice relaxation rates and we present a model for the distribution in terms of the dynamics of the magnetic defects. Our results explain the origin of recent puzzling 7Li NMR literature data on LiV2O4 and our model is likely applicable to other glassy systems.     

The first synthetic studies on pestalotiopsin A. A stereocontrolled approach to the functionalised bicyclic core

Pestalotiopsin A is a structurally unique, caryophyllene-type sesquiterpene which has shown immunosuppressive activity and cytotoxicity in preliminary assays. A stereocontrolled approach to the functionalised 2-oxabicyclo[3.2.0]-heptane core of pestalotiopsin A is described. This constitutes the first synthetic studies on pestalotiopsin A. Our approach includes a samarium(II)-mediated 4-exo-trig cyclisation and a trans-lactonisation process triggered by the addition of alkylytterbium reagents to a cyclobutanone intermediate. Further manipulation provides access to advanced intermediates which are excellent precursors for the future construction of the final ring of the target.     

High resolution spectroscopy of the 12Lambda B hypernucleus produced by the (e,e'K+) reaction

High-energy, cw electron beams at new accelerator facilities allow electromagnetic production and precision study of hypernuclear structure, and we report here on the first experiment demonstrating the potential of the (e,e'K+) reaction for hypernuclear spectroscopy. This experiment is also the first to take advantage of the enhanced virtual photon flux available when electrons are scattered at approximately zero degrees. The observed energy resolution was found to be approximately 900 keV for the (12)(Lambda)B spectrum, and is substantially better than any previous hypernuclear experiment using magnetic spectrometers. The positions of the major excitations are found to be in agreement with a theoretical prediction and with a previous binding energy measurement, but additional structure is also observed in the core excited region, underlining the future promise of this technique.     

Setting Company Stock Levels

This paper addresses the problem of how much total stock is required at a stocking location, with reference to a small number of overall characteristics. A relationship defining stock cover to throughput, number of items, overall service level, lead time and re-order interval is derived. Its use is seen as a strategic tool, to investigate the costs and benefits of changing service levels or amalgamating stocking points etc. The restrictions on its applicability are given.     

A reassignment of the 13C-NMR spectrum of the alkaloid ajmaline through the use of two-dimensional nmr techniques

The reassignment of the ¹³C chemical nmr spectrum of the alkaloid, ajmaline, is reported. An earlier assignment based on analogy to other alkaloids and deductions from molecular orbital theory was found to be partially in error. The present study uses broadband decoupled (both dimensions) proton-carbon shift correlation and long-range proton-carbon chemical shift correlation techniques. These experiments, in conjunction with earlier work by others on the assignment of the proton spectra, suffice to now unequivocably assign the ¹³C nmr spectrum of the title compound.     

On the computation of inclusion regions for partitioned matrices

In this paper, we consider the problem of computing inclusion regions for the eigenvalues of a partitioned matrix. The algorithms derived are special cases of a generalization of a result of Feingold and Varga which, in turn, is a generalization to the partitioned case of the well-known Gerschgorin circle theorem.This research was sponsored in part by the National Research Council of Canada.     

Analysis of corrosion and oxidation on metals by spectroscopic means

Summary This paper addresses three aspects of the surface analytical experiment which are felt to be particularly crucial in characterizing corrosion mechanisms: chemical speciation, microscopic analysis and improved control of experimental conditions. X-ray Photoelectron Spectroscopy (XPS or ESCA) has been particularly effective in differentiating chemical species. The major chemical use of XPS is limited however to the outer surface of the film. Depth profiling by ion bombardment frequently degrades the chemical information available in the film interior and at the metal-oxide interface, and this is often where corrosion mechanisms are established. Mechanical methods of film penetration are thus encouraged to use XPS to its maximum capability. Microscopic analysis of corrosion surfaces using Scanning Auger Microscopy (SAM) or Secondary Ion Mass Spectrometry can reveal effects such as grain boundary segregation and oxide nucleation. Another important aspect of corrosion film analysis is the preparation of the metal surface itself. The oxidized surface can be strongly influenced by preparation artefacts such as cold work or impurities. Three different studies are used to illustrate these aspects: (i) the analysis of a molybdenum inhibitor layer on a steel surface; (ii) the study of corrosion product release from 304-stainless steel; and (iii) the effects of H⁺ ion bombardment to anneal mechanical work on Ni-Cr alloy surfaces, prior to oxidation.

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Untersuchung der Korrosion und Oxidation an Metallen mit Hilfe spektroskopischer Methoden

Zusammenfassung Diese Arbeit betont drei Gesichtspunkte oberflächenanalytischer Untersuchung, die für die Charakterisierung von Korrosionsmechanismen als besonders wesentlich erachtet werden: die chemische Bindung, die mikroskopische Analyse und die verbesserte Steuerung experimenteller Bedingungen. Die Röntgen-Photoelektronenspektroskopie (XPS oder ESCA) ist für die Unterscheidung chemischer Spezies besonders erfolgreich gewesen. Die Anwendung von XPS beschränkt sich jedoch im wesentlichen auf die äußere Oberfläche einer Schicht. Die Aufnahme von Tiefenprofilen mit Hilfe von Ionenbeschuß vermindert häufig die chemische Information, die vom Schichtinnern und vom Metall-Oxid-Interface erhältlich wäre; und hier spielen sich oft die Korrosionsvorgänge ab. Mechanische Methoden des Dünnschichtabtrags sind somit aufgefordert, XPS bis an die Leistungsgrenze zu bringen. Mikroskopische Untersuchungen von Korrosionsschichten mittels Raster-Auger-Mikroskopie (SAM) oder Sekundärionen-Massenspektrometrie können Effekte wie die Korngrenzensegregation und die Oxidbildung aufdecken. Ein weiterer bedeutender Gesichtspunkt der Analyse von Korrosionsschichten ist die Behandlung der Metalloberflächen selbst. Die oxidierte Oberfläche kann durch Behandlungsfehler wie z.B. Kaltbearbeitung oder Verunreinigung stark beeinflußt werden. An Hand von drei verschiedenen Beispielen werden diese Aspekte illustriert: (i) die Analyse einer Molybdän-Schutzschicht auf Stahl; (ii) die Untersuchung von Korrosionsprodukten auf 304-Edelstahl; und (iii) die Effekte des H⁺-Ionenbeschusses zum Ausheilen mechanischer Schäden auf der Oberfläche von Ni-CrLegierungen, vor der Oxidation.

     

Separation of the alkali group by thin-layer chromatography using a binary solvent mixture

Summary The use of a binary solvent mixture (nitromethane/benzene) is shown to result in an improved separation of the polyiodides of the entire alkali group on thin-layers of air-most silica gel.

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Zusammenfassung Die Verwendung eines binären Lösungsmittelgemisches (Nitromethan-Benzol) führt zu einer verbesserten Trennung der Polyjodide der ganzen Alkaligruppe auf luftfeuchten Silikagel-Dünnschichten.

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Undergraduate Research Participant, State University of New York at Binghamton, 1966.