Kettenverzweigung bei der Polymerisation von Vinylchloracetat und Vinylacetat

Zusammenfassung Bei niedrigen Umsätzen und einer Polymerisationstemperatur von 50°C erhaltene Polyvinylacetate sind unverzweigt; das gleiche gilt für Polyvinylchoracetate. Bei diesen wurde die bei höheren Umsätzen auftretende Verzweigung durch Verseifung und Acetylierung der Polymeren sowie durch Messung von []-, und Werten an den Polymeren bestimmt. Eine Selbstverzweigung der wachsenden Kette konnte nicht gefunden werden. *** DIRECT SUPPORT *** A3615144 00012

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Chain branching in vinyl chloroacetate and vinyl acetate polymerization

Polymerization of vinyl acetate and vinyl chloroacetate to low conversions at 50°C gave unbranced polymers. The branching of polyvinyl chloroacetates at higher conversions was determined by hydrolysis and acetylation of the polymers and by measuring [], and . No self-branching of the growing chains could be found.

     

An alternative way to analyze quasi-elastic light scattering data for broadly distributed samples

In Quasi-Elastic Light Scattering (QELS), an apparent average hydrodynamic radius can be calculated from the measuredz-average translational diffusion coefficient D _z by using the Stokes-Einstein equation: withk _B,T and being the Boltzmann constant, the absolute temperature and the solvent viscosity, respectively. It is known thatR _{h, app} is not the same as R _{h z} because , especially when a sample is broadly distributed. In order to obtain R _{h z} instead ofR _{h, app}, an alternative way to analyze QELS data is proposed: at first, we manipulate the measured correlation functionb ^1/2|g ⁽¹⁾(t)| into a new function ; and then, we can analyze this new function to obtain an apparent parameter D_app and an apparent distribution width . We have shown that no matter how broadly a sample is distributed, D_app can be easily reduced to R _{h z} , and is directly related to the distribution width. In this report, besides using a simulated time correlation function, we also used two measured correlation functions of a latex dispersion with a broad particle size distibution and a polystyrene standard with a broad molecular weight distribution to demonstrate this alternative way.     

Electronic spectrum of dibiphenylene-ethene radical anion

The electronic absorption spectrum for the dibiphenylene-ethene radical anion ( ), generated electrochemically in dimethylsulfoxide solutions, is reported. Based on calculations by the LCAO-MO method in theHückel approximation and on the analysis of the band positions it is suggested that in the molecule two planar fluorenylidene fragments are twisted (60°) about the central C=C bond.

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Das Elektronenabsorptionsspektrum des Dibiphenylen-Radikalanions (Kurze Mitteilung)

Zusammenfassung Das Dibiphenylenethen-Radikalanion ( ) wurde elektrochemisch hergestellt und das Elektronenabsorptionsspektrum aufgenommen. Auf Grund von LCAO-MO Berechnungen in derHückel-Annäherung und der Analyse der Bandenlagen wird nahegelegt, daß im -Molekül zwei planare Fluorenyliden-Fragmente ca. 60° um die zentrale C=C-Bindung verdrillt angeordnet sind.

     

Method for the selection of the signal vs. concentration formula in the standard addition method

Summary It is shown how the accuracy and precision of the standard addition method depend on the formula used in approximation of the analytical calibration function. A method of selection of the best formula has been proposed and applied to the determination of Na in the presence of K and Ca. In the examples presented the following approximation formula has been applied: , where denotes the estimation of the emission measured at =589 nm, B ₀, B ₁ are the regression coefficients, the standard addition and q an empirical parameter in function f. The linear, parabolic, exponential, hyperbolic and logarithmic functions f have been tested. The hyperbolic function f proved to be most appropriate.

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Verfahren zur Auswahl der Beziehung Signal/Konzentration bei der Standardzugabemethode

Zusammenfassung Es wird gezeigt, daß Genauigkeit und Präzision beim Standardzugabeverfahren von der Formel abhängig sind, die zur Näherung der analytischen Funktion benutzt wird. Ein Verfahren zur Auswahl der am besten geeigneten Formel wird vorgeschlagen und zur Bestimmung von Natrium in Gegenwart von Kalium und Calcium angewendet. In den gegebenen Beispielen wird die folgende Näherungsformel verwendet: , wobei die Abschätzung der bei =589 nm gemessenen Emission bedeutet, B ₀ und B ₁ die Regressionskoeffizienten, die Standardzugabe und q einen empirischen Parameter der Funktion f. Lineare, parabolische, exponentielle, hyperbolische und logarithmische Funktionen wurden getestet, wobei sich die hyperbolische Funktion als am geeignetsten erwies.

     

Reaction graphs and a construction of reaction networks

Summary A general definition of reaction graphs is presented. For a pair of isomeric molecular graphs and , related by a chemical transformation , the reaction graph is determined using a maximal common subgraph defined for vertex mapping . A binary operation defined for graphs constructed over the same vertex set enables us to decompose the reaction graph into the sum of prototype reaction graphs. A decomposition of an overall reaction graph can be advantageously used for the construction of a reaction network. An oriented path in this network beginning at and ending at corresponds to a breakdown of the transformation into a sequence of intermediates.     

Configuration and conformation of substituted 1,3,2-dioxaarsenanes

The configuration and conformations often 2-, 4-, and 5-substituted 1,3,2-dioxaarsenanes were studied from their PMR spectra. Inversion of the shielding constants of protons in the 4, 6, and 5 positions and of methyl groups in the 5 position was established, and the axial orientation of the As-Cl and As-OR bonds, the equatorial orientation of the 4-CH₃ group, and the chair conformation of the six-membered heteroring were proved. The anisotropies of the diamagnetic susceptibility were estimated for the first time: and (dipole approximation); and (nondipole approximation). The cyclic torsion angle (= 58°) as found for 2-chloro-1,3,2-dioxaarsenane by the R-factor method. Conclusions regardiwng the conformation of the ring and substituents were confirmed by a study of the specific effect of an aromatic solvent on the position of the resonance lines.Communication I from the series Investigation of the Stereochemistry of Organic Arsenic Compounds by NMR Spectroscopy.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 457–463, April, 1973.     

Die Korrektur der Sekund?rfluorescenz in der R?ntgenspektrometrie

Zusammenfassung Die unmittelbar aus der Theorie abgeleitete Gl. (3) enthält keine explizite Korrektur der Sekundärfluorescenz, wie sie mit Gl. (4) in [3] vorgeschlagen wurde. Es war daher von Interesse, die Wirksamkeit der Gl. (4) im Vergleich mit Gl. (3) zu überprüfen, wobei der durchschnittliche Analysenfehler unbekannter Proben als Prüfkriterium diente.Die Anwendung auf theoretisch berechnete und praktisch gemessene Fe-Cr-Ni-Proben und auf Gemische von Metalloxiden ergab eine sehr geringe Überlegenheit von Gl. (4) über Gl. (3). Da erstere jedoch rechentechnisch komplexer aufgebaut ist, erscheint Gl. (3) als für die Praxis geeigneter.

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The correction of secondary fluorescence in X-ray spectrometry

Summary The Eq. (3) was directly derived from the theory and does not contain the correction of secondary fluorescence proposed by the authors of [3] with their semi-empirical Eq. (4) Therefore, it was of interest to test the efficiency of Eq. (4) in comparison with Eq. (3), the average analysis error serving as test criterion.The application to theoretically calculated and empirically measured Fe-Cr-Ni-systems and to mixtures of metal oxides resulted in a very small superiority of Eq. (4) to Eq. (3). Since Eq. (4) is mathematically more complicated than Eq. (3) the latter seems to be more suitable for practice.

     

ZumHunsdiecker-Abbau von 2-Acylcyclopropancarbonsäuren

2-Acylcyclopropane carboxylic acids (1) are degraded by aHunsdiecker reaction using red HgO/Br₂ to mixtures oftrans- andcis-2-bromo-cyclopropyl alkanones, the former being the major component. The starting materials may be easily prepared by reaction of stabilised S-ylides with ,-unsaturated oxo compounds or -acylvinyltriphenylphosphonium bromides.     

The thermodynamics of dilution ofn-dodecyltrimethylammonium bromide micelles in aqueous solutions

Summary The relative partial molal thermodynamic functions ₁ and have been derived from reported experimental light scattering and calorimetric measurements on micellar solutions ofn-dodecyltrimethylammonium bromide. It is shown that the magnitudes of the thermodynamic functions are considerably larger than can be accounted for by the interaction of the electrical double layers surrounding the micelles. Possible enthalpy changes arising from a change in micelle shape, size and degree of dissociation on dilution are discussed.

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Zusammenfassung Die relativen molaren thermodynamischen Partialfunktionen , andS ₁wurden abgeleitet aus Literaturwerten von Lichtstreuungsmessungen und kalorimetrischen Untersuchungen an mizellaren Lösungen vonn-Dodecyltrimethylammoniumbromid. Es wird gezeigt, daß die Zahlenwerte der thermodynamischen Funktionen erheblich größer sind als von der Wechselwirkung der elektrischen Doppelschichten zu erwarten ist, die die Mizellen umgeben. Mögliche Enthalpieänderungen, die sich aus Änderungen von Größe, Gestalt und Dissoziationsgrad bei Verdünnung herleiten, werden diskutiert.

     

Einflu? der Herstellungsbedingungen auf die Eigenschaften eines Celluloseaustauschers mit Salicyls?ure als funktioneller Gruppe

Zusammenfassung Die Darstellung eines Celluloseaustauschers mit Salicylsäure als funktioneller Gruppe wurde variiert, um die optimalen Bedingungen sowohl hinsichtlich eines raschen Austausches als auch im Hinblick auf eine hohe Kapazität zu finden. Zwei Arten von Cellulose (vernetzt und mikrokristallin) und verschiedene Reaktionszeiten wurden verwendet. Die Eigenschaften der Reaktionsprodukte wurden mit Hilfe von Titrationskurven zur Bestimmung der Kapazität und durch Messung des nicht-isotopen Austauschs und des Isotopenaustausches als Funktion der Zeit untersucht. Optimale Bedingungen wurden mit mikrokristalliner Cellulose und einer Reaktionszeit von 15 min erhalten.

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Effect of the conditions of preparation on the properties of a cellulose exchanger containing salicylic acid as a functional group

The preparation of a cellulose derivative containing salicylic acid as functional group was varied in order to find optimal conditions with respect to fast exchange as well as high capacity. Two kinds of cellulose (cross-linked and microcrystalline) and different reaction times were used. The properties of the products were investigated by titration curves to determine the capacity and by measuring the non-isotopic exchange and the isotopic exchange as a function of time. Microcrystalline cellulose and a reaction time of 15 min gave optimal results.

     

Effect of solvent on the partial molal volumes and heat capacities of nonelectrolytes

Group contributions to in seven solvents and to in three solvents have been tabulated. The variation of group parameters is discussed in terms of the solvent compressibility coefficient, _T. The scaled particle theory (SPT) is used to calculate cavity contributions to and C _p2 ^o . Interaction contributions are obtained from the cavity terms and and values estimated through the additivity schemes. values are more sensitive to solute-solvent interactions than in water and less sensitive in methanol. The SPT results for heat capacities support the concept of structural promotion by hydrophobic solutes in water.     

Conductance and transport numbers of acidified sodium aluminate solutions and the zero point of charge of aluminium hydroxide

Summary Conductance measurements of acidified sodium aluminate solutions showed a gradual drop as the alumina content of the solution increases. This behaviour was explained by adsorption of H⁺ ions, as visualised from linear plots of ( ₀–) per mole of alumina against (where ₀ is the specific conductance of the corresponding (NaOH + HCl), is the specific conductance of (sodium aluminate + HCl) and is the amount of H⁺ ions adsorbed per mole of alumina). Transport number experiments showed that alumina behaves as a non-electrolyte and that the transport number of the Cl– ion increases with increase in alumina content. This behaviour was explained on the basis of aggregation of water molecules around alumina.The zero point of charge of colloidally dispersed aluminium hydroxide was determined from potentiometric and conductance measurements.

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Zusammenfassung Leitfähigkeitsmessung von angesäuerten Natrium-Aluminat-Lösungen zeigen einen Abfall, wenn der Aluminat-Gehalt der Lösungen wächst. Dieses Verhalten wird durch Adsorption von Wasserstoff-Ionen erklärt, erkennbar aus der linearen Auftragung von ( ₀–) pro Mol/Aluminat gegen Dabei ist ₀ die spezifische Leitfähigkeit der entsprechenden (NaOH + HCl)-Lösung, die spezifische Leitfähigkeit vom Gemisch Natriumaluminat + HCl und der Betrag an Wasserstoffionen, adsorbiert pro Mol/Aluminat. überführungszahl-Experimente zeigen, daß Alumina sich nicht als Elektrolyt verhält und daß die überführungszahl für Cl^–-Ionen mit dem Alumina-Anteil wächst. Dieses Verhalten wird erklärt auf Grund einer Aggregation von Wassermolekülen um das Alumina.Der Neutralpunkt für Ladung von kolloidal dispergiertem Alumiumhydroxid wurde aus potentiometrischen und Leitfähigkeitsmessungen bestimmt.

     

Two Algorithms for Computing the Randles–Sevcik Function from Electrochemistry

We derive two expansions of the Randles–Sevcik function : an asymptotic expansion of for x and its Taylor expansion at any x ₀ . These expansions are accompanied by error bounds for the remainder at any order of the approximation.     

Semi-empirical molecular orbital calculations the electronic structure and the spin-orbit coupling in azabenzenes

Electronic structures of pyridine, pyrazine, pyrimidine and pyridazine are studied by a semiempirical SCF method for valence electron systems previously proposed by the present authors. The charge distributions, transition energies and oscillator strengths of these compounds are calculated. The calculated results show fairly good agreement with the observed ones. Using these results, we have further calculated the oscillator strengths of singlet-triplet transitions and the life times of the triplet states (). In this treatment, we have considered the mixing of various singlets with T ₁ and triplets with S ₀, and the effect of -electrons is studied.

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Zusammenfassung Es werden nach einer von den Autoren dieser Arbeit vorgeschlagenen Methode die Elektronenstrukturen von Pyridin, Pyrazin, Pyrimidin und Pyridazin studiert. Die halbempirische SCF-Methode für Valenzelektronensysteme gestattet die Berechnung der Ladungsverteilungen, Übergangsenergien und Oszillatorstärken, die in recht guter Übereinstimmung mit der Beobachtung stehen. Ferner werden die Oszillatorstärken von Singulett-Triplett-Übergängen und die Lebensdauer von Triplett-Zuständen () berechnet.

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Résumé Les structures électroniques de la pyridine, de la pyrazine, de la pyrimidine et de la pyridazine sont étudiées par une méthode SCF semiempirique pour les électrons de valence proposée précédemment par les auteurs. Les distributions de charge, les énergies de transition et les forces oscillatrices de ces composés sont calculées, donnant des résultats en bon accord avec l'expérience. De plus nous avons calculé les forces oscillatrices des transitions singulet-triplet et les durées de vie des états triplets (). Dans ce calcul nous avons inclus l'interaction de configuration et l'étude de l'effet des électrons .

     

The graphical representation of equilibrium for the isothermal and isobaric reactions of ideal gases

The equilibrium for the isothermal and isobaric reactions of ideal gases is investigated in virtue of the intuitionistic figure. The curve is similar to the curve of tangential function which has one inflection and two vertical asymptotes. The equation only has one root ξ _e and it is suitable to find ξ _e by dichotomy. For non-inert substance, when or x_i^0 $$" align="middle" border="0"> , to increase substance i will make an equilibrium shift in the direction to deplete substance i; when {\nu_i} \mathord{\left/ {\vphantom {{\nu_i} {\sum_i {\nu _i}}}} \right. \kern-\nulldelimiterspace} {\sum _i {\nu _i}}> 0$$" align="middle" border="0"> , to increase substance i will make an equilibrium shift in the direction to produce more substance i.     

Trennung des Strontiums von Yttrium (90Sr/90Y) mit Anionenaustauscher-Sulfaten

Zusammenfassung Die selektive Fällungssorption von Strontium an Dowex-I-Sulfat im Säulenverfahren als SrSO₄ aus 50%ig methanolischer Lösung erlaubt die rasche Gewinnung von fremdstrahlungsfreiem Yttrium-90 aus dem Zerfallsprozeß . Die Kontrolle des Trenneffektes erfolgt durch Bestimmung der Halbwertszeit des ⁹⁰Y. Je nach Länge der Austauscherschicht kann unter Beachtung der Bildungsschnelligkeit von ⁹⁰Y dieses mehrfach entnommen werden.

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Summary Selective precipitating Sorption of strontium as SrSO₄ on Dowex-I-sulphate in a column operation, using aqueous methanol solution (11), permits the isolation of pure ⁹⁰Y, produced by the decay process . The effect of separation may be controlled by determination of the half-life of ⁹⁰Y. Taking into account the velocity of formation ⁹⁰Y can be obtained several times according to the length of the ion-exchanger column.

     

Critical evaluation of the effective resonance energy concept and the epithermal neutron spectrum shape-factorα for reactor NAA purposes

The epithermal reactor neutron spectrum shape-factor, and the associated effective resonance energy for a given nuclide, are examined theoretically in great detail. First the necessity, meaning and importance of the choice of a reference neutron energy in a non-ideal spectrum (0) are explained. Next, the definition and practical calculation of are discussed, showing that the relation between the reasonance integrals in ideal and non-ideal spectra cannot be described adequately by two independent parameters and . The exact meaning of the logarithmic expression defining an independent of is clarified, its limits of validity are established as a function of and, as a result, it follows that relatively large systematic errors on can be introduced by its use. It is shown that is dominated by the first lowest resonance energies for a given nuclide, making its vulnerability to literature updates of resonance parameters almost equal to those of individual resonances. The effect, on the epithermal and total activation of specific nuclides, of large systematic and statistical errors on and, is calculated for a series of nuclides (different I₀/₀ and ) and irradiation facilities (different and _the), and represented graphically.Finally, the effect of important errors on and is calculated for final NAA results in terms of concentrations, botained by a comparator technique based on the¹⁹⁷Au reference nuclide. Conclusions are drawn concerning the impact of the foregoing on the usefulness of comparator type reactor NAA as an alternative to classical NAA using multi-element standards.     

Catalytic Mechanism of the “Noncatalytic” Autooxidation of Sulfite

Iron ions are shown to play a special role among transition metal ions in the oxidation of sulfite by oxygen. The thermodynamically favorable formation of chain carriers S : FeOH²⁺+ HSO₃ ^– Fe²⁺+ H₂O + , H _{r 298} ⁰ –250 kJ/mol accompanied by the regeneration of the active Fe(III) form in the reactions of Fe(II) with and HSO₅ ^–provides the efficient catalytic mechanism for sulfite consumption even at [Fe]₀ 10^–8mol/l. Any aqueous solution contains iron ions in this amounts. Thus, the noncatalytic oxidation of sulfite is in fact the catalytic reaction involving unavoidable microadmixtures of iron ions. Other transition metal ions (Mn²⁺, Co²⁺, etc.) can only enhance the catalytic effect of iron admixture.     

On the Pressure and Electric Field Dependencies of the Relative Permittivity of Liquids

The dependencies of the relative permittivity of over 50 liquids on the pressure P, as , and of some 40 liquids on the (square of the) electric field E at ambient conditions, as were obtained from literature data. The function was fitted to a simple expression in and the compressibility, _T. These data were used to obtain the limiting slope for the partial molar volumes and the electrostriction of electrolytes in various solvents.     

Kinetics and Equilibria for Complex Formation between Palladium(II) and Chloroacetate

Kinetics and equilibria for the formation of a 1:1 complex between palladium(II) and chloroacetate were studied by spectrophotometric measurements in 1.00 mol HClO₄ at 298.2 K. The equilibrium constant, K, of the reaction