Vergleichbare Kraftfelder vieratomiger Formylverbindungen

Comparable force fields for HCOO^–, HFCO, HClCO and HDCO have been calculated on the basis of internal coordinates. Linear relations between (i) the carbonyl bond order and the carbonyl stretching force constant, (ii) the sum of the three in-plane bending force constants and the hydrogen out-of-plane force constantf , (iii) a combination of orbital electronegativities andf , have been obtained. The observed in-plane vibrational frequencies have been calculated with an average error of 6.3 cm^–1 or 0.4%.

     

Separable single-particle Hamiltonian and its local equivalent

By using a method developed by Coz, Arnold and MacKellar the local equivalent of a single-particle potential discussed in a previous work is constructed and analyzed. The accuracy of the method is checked in the present case. The numerical examples refer to the low-energy elastic scattering of neutrons from nuclei described by a hole in a closed shell. The single-particle bound states are approximately described by harmonic oscillator wave functions. The results are similar to those derived by Coz, Arnold and MacKellar from non-local Hartree-Fock potentials.     

Über Reaktionen mit Betain, 6. Mitt.: Zur Chemie einiger Malonester-enolbetaine

Zusammenfassung IR-spektroskopische Untersuchungen an den Malonesterbetainen1–7 geben Hinweise auf die Schwerpunkte der Ladungsverteilung. Während die Lage der CO-Banden der Betaine1 und2 mit rein aliphatischer Esterkomponente auf vollständige Resonanz zwischen den Estercarbonylen hinweist, ist bei jenen mit aromatischen Estergruppen (4, 5 und7) eine CO-Funktion zu beobachten, die schon auf einen gewissen Ylidanteil schließen läßt. Damit im Einklang stehen auch ihre chemischen Eigenschaften. Z. B. zersetzt sich das Bisphenoxycarbonylbetain4 beim Schmelzpunkt vollständig. Die Thermolyse von1 und2 führt dagegen sowohl zu Picolin- als auch zu Kohlensäureestern. Der Reaktionsmechanismus wird diskutiert.

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Reactions with betain, VI: The chemistry of several malonate betaines

An IR-spectroscopic investigation concerning the malonate betaines1–7 gives an insight in the charge density distribution. The position of the C=O frequencies of the betaines1 and2 with alkyl ester groups shows complete resonance between the ester carbonyls, while with the phenolic esters4,5 and7 and C=O absorption is observed which shows a considerable ylid participation. the chemical properties of the betaines agree with this; e.g. the bis-phenoxycarbonylbetaine4 is decomposed totally at its melting point. However, the thermolysis of1 and2 gives picolinic acid esters and carbonic acid esters. The mechanism of these reactions is discussed.

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Herrn Direktor Dr. techn., Dr. rer. nat. h. c., Dr. phil. h. c.W. G. Stoll, Basel, mit besten Wünschen zum 60. Geburtstag gewidmet.     

Ein Algorithmus zur Berechnung der Vielfachheiten von Gewichten

Zusammenfassung Es wird ein Algorithmus zur Berechnung der Vielfachheiten der Gewichte von Darstellungen halbeinfacher Lie-Gruppen angegeben, der auf der Division des Weyl'schen Quotienten für den Charakter beruht. Dabei wird diese Division im Stiefel-Diagramm geometrisch interpretiert.

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This paper is concerned with the multiplicities of the weights of representations of semisimple Lie groups. an algorithm for the calculation of these multiplicities using the division of Weyl's quotient for the character is given. By means of the Stiefel diagram this division is geometrically interpreted.

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Meinem verehrten Lehrer, Professor E. Stiefel gewidmet     

Upper critical fields of Nb∼3Au,Nb3Au0.7Pt0.3 and Nb3Pt

Upper critical field measurements of the A15 type compounds Nb_～3Au,Nb₃Au_0.7Pt_0.3 and Nb₃Pt having T_c values of 10.7, 13.0 and 8.7K, respectively, show H_c2(0) values of 235, 295 and 125 kG, respectively. The data for the compounds containing Au fit closely calculations for a dirty type II superconductor with no paramagnetic limiting, but data for Nb₃Pt are slightly above these calculations.     

Observation of the decay τ → πv

The decay of the heavy lepton τ into πv has been established using the magnetic detector PLUTO. The branching ratio is determined to be BR(τ→πv)=(9.0 ± 2.9)% with an additional systematic uncertainty of 2.5%. This value is in good agreement with the theoretical prediction.     

Analytical applications of organized assemblies for on-line spectrometric determinations: present and future

An amphiphile (surfactant) spread on water can lead to the formation of different aggregates: vesicles, miscelles, emulsions or microemulsions; depending on its concentration; its molecular structure and/or the experimental conditions. Such aggregates, (a) may concentrate products, reactants or analytes and so improve the analytical sensitivity and (b) may solubilize such substances and so favorably change the analytical selectivity. Bilayer membrane vesicles for instance, apart from their wide applications in cosmetic and pharmaceutical industries, have a great analytical potential due to their ability to (i) reversibly sequester metal ions avoiding matrix interference and (ii) improve cold vapor (Hg and Cd) and hydride (As, Se, Pb) chemical generation. Micellar solutions have also found wide applications in different areas of analytical chemistry, showing their capacity to concentrate and separate a significant variety of analytes. Among the numerous micelle-based separation techniques, cloud point extraction offers an excellent enrichment factor for metal ions, allowing their quantification at microgram/litre levels. Also agitating a mixture of water, oil and one or more surfactants under controlled experimental conditions, a cloudy mixture (emulsion) or a transparent solution (microemulsion) can be formed. Adequate formulation is necessary in order to obtain a stable organized media. To fulfill this requirement, a major effort is necessary in order to shorten the gap between the current knowledge on this topic and the promising field of applications that await development. Recent publications show that self-assembly structures from highly viscous samples can be accomplished on-line with the advantages of drastically reducing the time of analysis and assuring the absolute control over the stability of the aggregate. Flow systems allow effective mixing of samples with added surfactant and provide continuous pumping of the resulting mixture to sensitive detectors for the on-line determination of different analytes in complex samples.     

Lanthanide transport in stabilized zirconias: interrelation between ionic radius and diffusion coefficient

The diffusion of all stable lanthanides was measured both in calcia stabilized zirconia (CSZ) and in yttria stabilized zirconia (YSZ) in the temperature range between 1,286 and 1,600 degrees C. The lanthanide diffusion coefficients obtained increase with increasing ionic radius. The experimental activation enthalpy of diffusion is near 6 eV for CSZ and between 4 and 5 eV for YSZ and is not strongly affected by the type of lanthanide. The results were correlated with defect energy calculations of the lanthanide diffusion enthalpy using the Mott-Littleton approach. An association enthalpy of cation vacancies with oxygen vacancies of about 1 eV (96 kJ/mol) was deduced in the case of CSZ, while there is no association in the case of YSZ. Furthermore, the change in diffusion coefficients can be correlated to the interaction parameter for the interaction between the lanthanide oxide with zirconia: The higher the interaction parameter, the higher the lanthanide diffusion coefficient.     

Efficient synthesis of B-alkylated oxazaborolidines derived from ephedrine and norephedrine

[reaction: see text] Representative B-butyl- and B-methyl-1,3,2-oxazaborolidines derived from ephedrine and norephedrine were prepared in good yield and excellent purity by one-pot treatment of B-H oxazaborolidines with the corresponding organolithium reagent and subsequent hydrolysis of the cyclic borohydride intermediate with anhydrous ammonium chloride.