Thermal properties of tetrahydroperparine derivatives

The thermal behaviour of tetrahydroperparine (THP) and its derivatives with various acids has been investigated. The acid is liberated from the formate derivative basically in two steps, while the other aliphatic acids are released quantitatively before the thermal decomposition of the THP molecule. The thermoanalytical curves, electrical conductivity data measured in the molten phase, and infrared spectra prove that while part of the formic acid is hydrogen-bonded the other part is bound ionically in the molecule. It may be assumed that the marked biological activity of the compound can be explained by this difference in the nature of the bonds.     

Novel electroanalytical techniques for pollution analysis

Summary Two new analytical techniques are described. The so-called injection technique operates on evaluating a dynamic concentration signal as a result of following the concentration change in a certain part of a flow-through channel after injecting a sample or reagent at a small volume into the current of an appropriate solution flowing at a constant rate.The second technique, the programmed coulometric titration technique, also uses the flow-through channel principle; that means this novel technique allows the more precise titrimetric way of analysis in flowing solutions. In the case of both techniques potentiometric and voltammetric detectors were involved. Several examples proved the multifold advantages of these techniques for environmental analysis.

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Neue elektroanalytische Verfahren für die Umweltanalyse

Zusammenfassung Zwei neue Methoden werden beschrieben. Die sog. Injektionstechnik wertet ein dynamisches Konzentrationssignal aus, das sich aus der Änderung in einem Durchflußkanal ergibt, wenn Probe oder Reagens in kleinen Volumina in einen konstant fließenden Flüssigstrom injiziert werden. Das zweite Verfahren, die programmierte coulometrische Titration, erlaubt die Anwendung der genaueren titrimetrischen Technik auf fließende Lösungen. Bei beiden Methoden werden potentiometrische und voltammetrische Detektoren verwendet. Mehrere Beispiele zeigen die vielfachen Vorteile dieser Verfahren bei der Anwendung auf die Analyse von Umweltmaterial.

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

Thermogravimetrische Untersuchung an den Kristallhydraten der Acetate einiger Zweiwertiger Metalle

Journal of Thermal Analysis and Calorimetry - Die Acetate Mg(OCOCH3)2 · 4H2O, Ca(OCOCH3)2 · H2O, Mn(OCOCH3)2 · 4H2O, Co(OCOCH3)2 · 4H2O, Ni(OCOCH3)2 · 4H2O,...     

Spectrophotometric determination of the protolytic dissociation constants of the new chromogenic reagent "palladiazo"-I Investigations with sodium hydroxide, perchloric acid and different aqueous buffer solutions

The "palladiazo" reagent has been subjected to a detailed spectrophotometric investigation in concentrated perchloric acid, different aqueous buffers and concentrated sodium hydroxide solutions. K(1)-K(10) and (1)-(10) values corresponding to the instability constants of the protolytic equilibria involved and to the molar absorptivities at 540 and 630 run of the different proton complex species of the system have been calculated by a number of analytical and graphical spectrophotometric methods. Special attention has been paid to the study of the complicated phenomena implied by the interaction of the reagent with perchloric acid, which has been shown to give rise to alteration of the initial isomeric composition of the reagent and to the formation of addition and/or oxidation products derived from side-reactions undergone by the reagent with the medium. All the instability constants and molar absorptivities, which have been determined by several methods, are tabulated for comparison.     

Influence de la temperature de polymerisation sur le taux de branchement de divers polybenzofurannes obtenus par amorçage cationique

Several polybenzofuranes, obtained by cationic initiation at various temperatures, have been fractionated by preparative G.P.C. The fractions have been studied by various physical methods, mainly osmometry, light scattering, viscometry and G.P.C. These determinations have been made in benzene and the Mark-Houwink relations have been obtained. From the differences observed between these various relations, the gyration radii and the determination of branching indexes, we have found very numerous branches in the samples obtained at the highest temperatures. These branches very probably result from a Friedel-Crafts attack on benzene rings by the carbocations of growing chains. Quantum chemistry determinations are in agreement with this view.     

Influence of a silyl group on an allylic position. A theoretical approach

Allylsilanes show in certain cases a behaviour towards electrophiles which is opposite to that of its carbon homologues. Theoretical calculations using Dewar's MINDO/3 method performed on 3-methyl 3-butenyl trimethylsilane and 2-methyl 2-butene show that geometrical optimization leads to a silicon-allylic carbon bond nearly parallel to the double bond π cloud, and both net atomic charges and HOMO coefficients indicate an inversion between these two substrates.     

Excess molar enthalpy of binary mixtures of hexane+ethyl benzene, <Emphasis Type="Italic">o</Emphasis>-xylene, <Emphasis Type="Italic">m</Emphasis>-xylene and <Emphasis Type="Italic">p</Emphasis>-xylene at 298.15 K

Summary This paper reports excess molar enthalpies of the binary systems hexane+ethyl benzene, hexane+o-xylene, hexane+m-xylene and hexane+p-xylene at 298.15 K and atmospheric pressure, over the whole composition range. The data was measured directly using a Calvet microcalorimeter. The excess magnitude was correlated to a Redlich-Kister type equation for each mixture. Also, we will discuss the results for the four mixtures studied here and by comparison with the same binary systems but containing propyl propanoate as first component. Finally, we will correlate our results with the Nitta-Chao and the three UNIFAC theoretical approximations.     

Ein Dreikomponenten-Zweiphasensystem für die schnelle Flüssigkeits-Chromatographie

Zusammenfassung Für die Hochdruck-Flüssigkeits-Chromatographie wird ein Dreikomponenten-Zweiphasensystem beschrieben. Die Mischungslücke besteht zwischen dem wenig polaren Methylenchlorid und dem stark polaren Wasser und kann durch Zugabe von Äthanol als Lösungsvermittler geschlossen werden. Durch den Anteil der stark polaren Komponente in den jeweils koexistenten Phasen ist die Polarität von stationärer und mobiler Phase als stationäre gebunden und aus der mobilen immer wieder regeneriert. Durch Verteilungs-Chromatographie in der Mischungslücke ist eine Vielzahl von Stoffklassen der Trennung zugänglich, so z.B. Corticosteroide, Östrogene, Phenole, Phenolcarbonsäuren usw.

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A three-component two-phase system for high speed liquid chromatography

Summary High pressure liquid chromatography with a three-component two-phase system is described. For the less polar methylenechloride and the highly polar water a wide range of incomplete miscibility exists which can be decreased with ethanol. The water content of the coexistent phases determines the polarity of the stationary and the mobile phases. The more polar phase is adsorbed on silicagel as the column support material and serves as the stationary phase. Numerous compounds can be separated by partition chromatography between the coexistent phases, for instance; corticosteroids, estrogens, phenols, phenol-carboxylic acids and so on

     

Calculation of molecular geometries by SCF perturbation theory

An SCF perturbation method for investigating the effects of an arbitrary change in nuclear configuration on the electronic structure of a molecule is reported. Illustrative calculations for CO₂ and CH₃OH are presented. It is found that, when taken to second order, the error in the calculated change in energy which results from a change in nuclear configuration is typically in the range of 0.1 to 7%.     

Conformation et spectres de vibration des dérivés halogénés du cyclopentane à basse température

A conformational study by vibrational analysis of cyclopentane and halogenocyclopentanes is performed on the basis of the Raman spectra at a very low temperature and the infrared spectra of these molecules trapped in a rigid matrix.