Untersuchungen der Absolutintensität der Röntgenkleinwinkelstreuung an Polyäthylenterephthalat in Abhängigkeit von den Kristallisationsbedingungen

Zusammenfassung Es wurden Messungen der Dichte sowie der absoluten Intensität der Röntgenkleinwinkelstreuung an teilkristallinem Polyäthylenterephthalat durchgeführt. Aus den erhaltenen Resultaten wurden der Volumenanteil der Kristallite, die Dichte der Kristallitek und die Dichte der nichtkristallinen Bereiche _a berechnet. Bei Proben, die bei tiefer Temperatur kristallisiert worden waren, lagk unterhalb von 1,455 g/cm³, dem Wert, der aus den Abmessungen der Elementarzelle einer möglichst gut kristallisierten Probe bestimmt wurde. _a war bei allen Proben kleiner als die Dichte des völlig amorphen Stoffes. lag jeweils über dem Wert, der allein aus der Dichte in konventioneller Weise bestimmt wurde.

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Summary Measurements of the density and the absolute intensity of small angle X-ray scattering of semicrystalline polyethylenterephthalate were performed. From the results obtained the crystalline volume fraction, the density of the crystalsk and the density of the noncrystalline regions _a were calculated. With samples crystallized at lower temperatures,k lies below 1,455 g/cm³, the value obtained from the crystal unit cell dimension on a material crystallized as well as possible. _a is generally smaller than the density of a completely amorphous sample. For higher temperatures of crystallization, is larger than the values obtained simply from the density by conventional methods.

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Vorgetragen auf der Arbeitssitzung des Fachausschusses Physik der Hochpolymeren in der Frühjahrstagung Berlin 1971 vom 9. bis 13. März des Regionalverbandes Physikalische Gesellschaft zu Berlin.

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Wir danken Herrn Prof. Dr.E. W. Fischer für zahlreiche wertvolle Diskussionen. Unser Dank gilt ferner der Deutschen Forschungsgemeinschaft für die finanzielle Unterstützung dieser Arbeit, sowie der Fa. Kalle A. G., Wiesbaden, für die Überlassung der Folien.     

Elastizitätsmodul und Dichte von kaltverstrecktem und druckbehandeltem Polyäthylen

Zusammenfassung Proben aus Polyäthylen hoher Dichte wurden bei Raumtemperatur mit verschiedenen Geschwindigkeitenv _ver auf einer Zugprüfmaschine verstreckt. Beiv _ver 10 mm/min beobachtet man eine fast isotherm verlaufende inhomogene Deformation, die zu Verstreckungsgraden=8–13 und mittleren Dichten = 0.80 g/cm³ in den verstreckten Probenbereichen führt. Die bei höherenv _ver bis zu 50 mm/min eintretende adiabatische Erwähnung ergibt höhere Verstreckungsgrade=13–18 und geringere Dichten = 0.64 g/cm³. Es existiert kein natürlicher Verstreckungsgrad. Der Dichteabfall mit zunehmendem kann durch eine Gerade repräsentiert werden; der ElastizitätsmodulE ergibt eine mit zunehmende Kurve.Nach einer Druckbehandlung der Proben mit 5600 bar bei Raumtemperatur erreichte ihre Dichte fast wieder den Anfangswert vor der Verstreckung, wobei keine Abhängigkeit von oder anderen Parametern zeigte. Der ModulE hatte zugenommen, aber nicht proportional zur Dichte. Der Vergleich von undE verstreckter Proben vor und nach der Druckbehandlung weist auf den Netzwerkcharakter von kaltverstrecktem Polyäthylen hin.Herrn Prof. Dr. K. Ueberreiter zum 70. Geburtstag gewidmet.     

Marginal electron density and density-difference functions

Summary For visual analysis of the density reorganization and distortion, the one-dimensional cut (x, y ₀,z ₀) and the two-dimensional cut (x, y, z ₀) of the three-dimensional electron density difference function (x, y, z) are frequently employed. However, these cut functions do not satisfy any sum rules in contrast to the original difference function (x, y, z). To avoid this difficulty, the use of the marginal electron density functions _x (x) and _xy (x, y) and their difference functions _x (x) and _xy (x, y) is proposed. The marginal densities are condensation of the three-dimensional density onto a particular plane or line of our interest, and they satisfy the sum rule (i.e., the conservation of the number of electrons) exactly. Some basic properties of the marginal electron density are clarified for typical diatomic molecular orbitals. An illustrative application is given for the bonding and antibonding processes in the H₂ system.     

Spin density calculations in semiempirical restricted and unrestricted SCF MO methods

In the present paper spin densities are calculated by ten methods on chosen radical systems. - interaction parameters for the individual methods are determined by McConnel's relation a _i =Q _i and by that of Colpa-Bolton a _i =(Q+K _i ) _i and the correlation between the results of the individual methods is studied.

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Zusammenfassung In der vorliegenden Arbeit werden Spindichten anhand von zehn Methoden an ausgewählten Radikalsystemen ermittelt. Die --Kopplungsparameter für die einzelnen Methoden werden nach den McConnell a _i =Q _i - und Colpa-Bolton a _i =(Q+K _i ) _i -Beziehungen bestimmt. Die zwischen den Ergebnissen der einzelnen Methoden bestehende Korrelation wird untersucht.

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Résumé Dans ce travail les densitées de spin sont calculées par dix méthodes sur un système des radicaux choisis. On détermine des parametres - d'interaction pour les méthodes individuelles dans la relation de McConnell a _i =Q _i et celle de Colpa-Bolton a _i =(Q+K _i ) _i et étudie la correlation entre les résultats des méthodes individuelles.

     

Molekülordnung und Kristallinität in Polyhexamethylenadipamid

Zusammenfassung Kalorimetrische, röntgenographische und IR-spektroskopische Untersuchungen und Dichtemessungen ergaben für PA 66 eine bei anderen Polymeren unbekannte Anomalie. Die Abhängigkeit der Röntgenkristallinitätw _c und der kristallinitätsproportionalen Größen (experimentelle Schmelzwärme H ^*, IR-Bandenintensität) vom spezifischen Volumen ändert sich mit den Kiistallisationsbedingungen. Dies ist die Folge eines konformationsbedingten Übergangs zwichen zwei triklinen Modifikationen unterschiedlicher Dichte. Für aus der Schmelze, dem Glaszustand und verdünnter Lösung kristallisierte Proben treten bei allen drei Meßmethoden hinsichtlich der Abhängigkeit vom spezifischen Volumen drei Bereiche auf. Bereich I: Die Proben enthalten 1-Kristalle mit _c ^I =1,22 =1,22 gcm-³,H _M ^I =235 Jg^–1 und=1,095 gcm _u–3. Bereich II: Die Proben enthalten _II -Kristalle mit _cII=1,165 gcm^–3.H _M ^II =185 Jg _u ^–1 1 und pa =1,095 gcm^–3. Bereich III: Übergangsbereich, in dem sich das spezifische Volumen stärker ändert als we und H ^*, weil die Kristalldichte zwischen _c ^I und ell variiert.Die _c -Wertr wurden außer durch Extrapolation über dem spezifischen Volumen auch aus der Invarianten der Röntgenkleinwinkelstreuung bestimmt. In allen Fällen ist eine .röntgenographische Kristallinitätsbestimmung bei PA 66 willkürfrei und reproduzierbar möglich. Aus Dichte oder Schmelzwärme kannw _c unter Verwendung der ermittelten _c- und H_M-Werte nur bestimmt werden, falls die Proben den Bereichen I oder II angehören. Mit den üblichen Verarbeitungsmethoden erhält man jedoch meist Proben im Bereich III.

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Summary From the results of calorimetric, X-ray and infrared spectroscopic investigations and density measurements an anomaly is found for polyamide 66 which is not known for other polymers. The dependence of X-ray crystallinityw _c and other properties proportional to crystallinity (experimental heat of fusion H ^*, intensity of IR-absorptions) on the specific volume varies with the conditions of crystallization. This is due to a conformational transition between two triclinic modifications with different densities.Samples of polyamide 66 were isothermally crystallized from the melt, from dilute solution and from the glassy state at different crystallization temperatures. The results of each of the three experimental methods, when plotted versus specific volume, exhibit three sections Section I: The samples contain _I -crystals with _c =1.22 gcm^–3, H _M ^I = 235 Jg^–1 and _a =1.095 gcm^–3 Section II: The samples contain air-crystals with _c ^I =1.165 gcm-3, H _M ^II =185 Jg^–1 and ppa =1.095 gcm^–s; Section III: Transition range, where the change in the specific volume is greater than that inw _c and H ^*, because the crystal density varies continuously between _c ^I and _c ^II The crystal densities have been determined not only by specific volume extrapolations, but also from the mean square electron density fluctuation of the small angle X-ray scattering. In all cases it is possible to determine the crystallinity of polyamide 66 from X-ray measurements in an unequivocal and reproducible way. The calculation of crystallinity from density or heat of fusion is only possible, if the samples belong to section I or II. The usual processing methods, however, produce samples which belong to section III.

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Mit 15 Abbildungen und 2 Tabellen

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Herrn Professor Dr. Horst Pommer zum 60. Ge burtstag gewidmet.     

The relation of directly bonded C-H coupling constants to s-characters revisited

Summary Following earlier theoretical studies of orbital delocalization effects on one-bond ¹³C-H coupling constants (¹ J _CH) an approximate proportionality of (¹ J _CH) to ^3/2, where is the s-character of the carbon hybrid orbital appropriate to the construction of the best localized molecular orbitals, is predicted and verified by using published data. It is proposed that this proportionality should replace the previous linear correlations of (¹ J _CH) with , which involve large additive constants.     

Augmentation of the Generalised n×n Eigenvalue Equation to a Generalised (n+1)×(n+1) Eigenvalue Equation

Generalised n×n eigenvalue equation B| _i = _i S ^b | _i (i=1,...,n) where B and S ^b are n×n Hermitian matrices while S ^b is in addition positive definite is considered. This equation is augmented to a generalised (n+1)(n+1) eigenvalue equation H| _k = _k S| _k (k=1,...,n+1) where Hermitian matrices H and S represent matrices B and S ^b , respectively, augmented by one additional row and one additional column. It is shown how the eigenvalues _k and the eigenvectors | _k of the augmented eigenvalue equation can be expressed in terms of the eigenvalues _i and the eigenvectors | _i of the original eigenvalue equation. Operation count to obtain by this method all augmented eigenvalues and eigenvectors is of the order O(n ²). Unless matrices involved are of some special kind such as sparse matrices or alike, this operation count is one order of magnitude smaller than operation count required by other presently known methods. In many practical cases operation count to obtain a single selected eigenvalue and/or eigenvector by this method is of the order O(n). In the case of the generalised eigenvalue equation, all other methods usually require again O(n ³) operations, even if only a single eigenvalue and/or eigenvector is required. Thus in many cases of interest operation count to obtain a selected eigenvalue and/or eigenvector by this method is two orders of magnitude smaller than operation count required by other methods.     

Comparison Between a Generalized Electronic Diabatic Approach and the Born–Oppenheimer Separation Scheme in Inertial Frames

We discuss a generalized electronic diabatic (GED) approach to diagonalize the exact Hamiltonian of an n-electron system which embeds an external background of positive charges. This Hamiltonian, denoted by _e(q,), is defined in an inertial frame, and it contains a quantum part (the electrons with coordinates q) and a classical part (the external charges in a three-dimensional configuration ). We derive a GED basis set { _k (q)} using an operator _e(q,⁰) for a single configuration ⁰, and then show that these are also eigenfunctions for any other _e(q,); only the ordering of eigenvalues may depend on (i.e., k=k()). The GED functions can also be used to represent the eigenstates of a fully quantum-mechanical system of electrons and nuclei. We discuss briefly the differences between the present procedure and the standard Born–Oppenheimer (BO) technique in the clamped-nuclei approximation. As illustration, we show how chemical changes emerge as transitions among diabatic states mediated by an electromagnetic field.     

Röntgenuntersuchungen zur Kristallstruktur von Polybutylenterephthalat (PBT)

Zusammenfassung Polybutylenterephthalat (PBT) gewinnt als Spritzgußmaterial und als Faserrohstoff zunehmend an Bedeutung. Die thermischen und mechanischen Eigenschaften des PBT sind von denen des Polyäthylenterephthalates (PET) erheblich abweichend. Die vorliegende Arbeit soll einen Beitrag liefern, die abweichenden Ergebnisse deuten zu können.Deswegen wurden die Gitterzelle und die Kettenanordnung im Kristallverband des PBT untersucht. Aus Röntgenmessungen ergaben sich die folgenden Gitterzellenparameter:a=4,83 Å,b=6,05 Å,c=11,45 Å,=100,5°,=117°,=110,8°.Damit ergibt sich eine Kristalldichte von=1,433 g/cm³ im Vergleich zu=1,515 g/cm³ beim PET.Mit der Annahme einer abgewinkelten Kettenkonformation kann in befriedigender Weise die verkürzte Faseridentitätsperiode und die gegenüber dem PET verlängerte Zellenkante a des PBT erklärt werden.

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Summary Polybutylenterephthalate (PBT) is a new molding and fibre spinning material for industrial applications. The thermal and mechanical properties of PBT are quite different from those of polyethyleneterephthalate (PET).The unit cell of PBT was found by X-ray diffraction studies to be triclinic, similar to that of PET, but having the parameters:a=4.83 A,b=6.05 Å,c=11.45 Å,a=100.5°=117°,=110.8°. This gives a crystalline density of=1,433 g/cm³ compared with=1.515 g/cm³ for PET.Since a completely extended PBT chain would theoretical have a repeat length of 13.25 Å the above unit cell requires a kinked chain conformation. The increaseda axis dimension, in comparison to PET would be in agreement with this conclusion.

     

Die Bedeutung der mittleren Probendichte für die quantitative Interpretation der Röntgenkleinwinkelstreuung teilkristalliner Polymerer

Zusammenfassung Die Bestimmung von überstrukturdaten polymerer Lamellenclustersysteme kann über Modellrechnungen der Röntgenkleinwinkelstreukurven erfolgen. Es wird gezeigt, daß in vielen Fällen die Modulation der Streukurve nicht allein durch die innere Struktur der Cluster bestimmt ist, vielmehr muß die mittlere Elektronendichte der Umgebung der Cluster mitberücksichtigt werden. An den Systemen HDPE, PP und iPS/PPO wird gezeigt, daß die Verwendung eines einfacheren Modells, in dem die kristalline Dichte _c = 1 und die amorphe Dichte _a = 0 gesetzt wird (schwarzweiß-Modell), für kleine Lamellenzahlen pro Cluster zu einer Scheinanpassung führt. Die BerÜcksichtigung der mittleren Probendichte fÜhrt zu abweichenden Anpassungsparametern bei der Berechnung der experimentellen Streukurve und damit zu anderen Über-rstrukturdaten. Der Einfluß der Umgebungsdichte wird vernachlässigbar klein, wenn die Zahl der lagekorrelierten Lamellen pro Cluster größer als 10 wird.

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Summary Superstructural parameters of polymeric material composed of clusters of lamella-shaped crystals can be obtained by model-calculations of their small-angle x-ray scattering curves. In this paper it has been demonstrated, that in many cases the modulation of the scattering curve is determined not only by the inner structure of the cluster but also dependent on the average (electron) density of the cluster environment, the mean sample density. Discussing the SAXS of the systems HDPE, PP and iPS/PPO it has been shown, that the use of a simpler ,black-white model, in which the crystalline density has been set _c = 1 and the amorphous density _a = 0, leads to a phony fit. The incorporation of the mean sample density into the model yields a different set of parameters. The mean sample density can be neglected as soon as the number of lamellae per cluster exceeds the value of 10.

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Mit 4 Abbildungen und 1 Tabelle     

Light scattering studies on solutions of chlorinated rubber

Summary Measurements have been made of the depolarisation factors _u , _v , _h, and the intensity of scattering in the horizontal transverse direction, in the case of solutions of four different samples of chlorinated rubber in carbon tetrachloride. The size, shape and molecular weight of the micelles have been deduced by the application of the light scattering theories of Gans, Vrklajan and Katalinic and Debye. The extent to which the degradation of the rubber molecule occurs on chlorination has also been assessed.

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Zusammenfassung Für Lösungen von vier verschiedenen Proben von chloriertem Kautschuk in Tetrachlorkohlenstoff wurden Messungen der Depolarisation und der Lichtstreuung durchgeführt. Größe, Gestalt und Molekulargewicht wurden unter Verwendung der Theorien der Lichtstreuung von Gans, Vrklajan, Katalinic und Debye abgeleitet. Die Stärke des Abbaues, dem die Kautschukmoleküle bei der Chlorierung unterworfen sind, wurde abgeschätzt.

     

CPS K 843 Radiation-induced crosslinking: Effect on structure of polyethylene

Branched polyethylene irradiated (0–400 Mrad) with a Co⁶⁰ source at room temperature under vacuum was studied by density, wide- and small-angle X-ray scattering (WAXS and SAXS) measurements. The radiation effects on the structure of bulk, branched polyethylene are quite similar to those observed by others on single crystals or oriented preparations. These effects include changes in bulk density, crystallinity(w _c orv _c) and¯d ₁₀₀ and¯d ₂₀₀ spacings as a function of irradiation. A decrease in crystallinity is seen to begin at radiation dose 100 Mrad whereas lattice expansion indicating onset of an orthorhombic-hexagonal transition can begin as low as 10 Mrads. The decrease in crystallinity can be attributed to additional lattice distortions primarily introduced by the crosslinks occurring at the lateral grain boundaries, while lattice expansion can be associated with the same crosslinking mechanism which begins at the defects both within the crystals as well as those outside the crystals at the lateral grain boundaries. Strong evidence for a primary crosslinking-at-the-defects mechanism has also come from _c and _a data obtained in this study as a function of radiation dose. The same data have also led to an excellent correspondence between the measured density crystallinityv _c and the measured WAXS crystallinityw _c. Without consideration of the effects of crosslinks on _c and _a one would have obtained a divergence of the two crystallinities, especially at radiation doses greater than 100 Mrads.Dedicated Prof. Dr. R. Bonart on the occasion of his 60^th birthday     

A desk computer program for the calculation of rate constants

A desk computer program has been written in BASIC programming language to optimize the values of rate constants determined from kinetic measurements of time and concentration data. The program is capable of the simultaneous refinement of a maximum of 5 rate constants. A FORTRAN version using the Gear method is also available.

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, BASIC , . 5 . FORTRAN .

     

Complex formation between nickel(II) and 2-(2-aminoethyl) benzimidazole: A kinetic and equilibrium study

Summary The reversible complex formation between 2-(2-aminoethyl) benzimidazole (AEB) and nickel(II) was studied by stopped flow spectrophotometry at I = 0.30 mol dm^–3. Both the neutral and monoprotonated form of AEB reacted to give the NiAEB²⁺ chelate. At 25 °C, the rates and activation parameters for the reactions Ni_II + AEB NiAEB²⁺ and Ni^II + AEBH⁺ NiAEB²⁺ + H⁺ are k _f ^L(dm^–3 mol^–1 s^–1) = (2.17 ± 0.24) × 10³, H (kJ mol^–1) = 40.0 ± 0.8, S (JK^–1 mol^–1) = – 47 ± 3 and k _inff ^pHL (dm³ mol^–1 s^–1) = 33 ± 10, H (kJ mol^–1) = 42.0 ±2.7, S (JK^–1 mol^–1) = – 72 ± 9. The dissociation of NiAEB²⁺ was acid catalysed and k _obs for this process increased linearly with [H⁺] in the 0.01–0.15 mol dm^–3 (10–30 °C) range with k _H(dm³ mol^–1s^–1) (25 °C) = 329 ± 6, H (kJ mol^–1) = 40 ± 2 and S (JK^–1 mol^–1) = – 61 ± 8. The results also indicated that the formation of NiAEB²⁺ involves a chelation-controlled, rate-limiting process. Analysis of the S ° data for the acid ionisation of AEBH _inf2 ^p2+ and the formation of NiAEB²⁺ showed that the bulky AEBH⁺ ion has a solvent structure breaking effect as compared to AEB [s _aqS ° (AEBH⁺) – s _aq ° (AEB) = 69 JK^–1 mol^–1], while AEBH _inf2 ^p2+ is a solvent ordering ion relative to NiAEB²⁺ [s _aq° (NiAEB²⁺) – ovS _aq ° (AEBH _inf2 ^p2+ ) = 11 JK^–1 mol^–1].Author to whom all correspondence should be directed.     

Schnelle dynamische H2O/PERCOLL-Dichtegradienten für Mikropartikel in der analytischen Ultrazentrifuge

Zusammenfassung Es wird über eine schnelle Ultrazentrifugen-Analysenmethode berichtet, die es ermöglicht, innerhalb von 10 bis 30 min Mikropartikel im Dichtebereich 0,85< <1,15 g/cm³ nach der Partikeldichte zu fraktionieren und die Dichte selbst sowie eventuell vorliegende Dichteverteilungen zu bestimmen, was Aussagen über die chemische Zusammensetzung der Partikel und eine eventuelle chemische Uneinheitlichkeit erlaubt. Dazu wird innerhalb von 20 min im Schwerefeld einer analytischen Ultrazentrifugenzelle durch sedimentierende, extrem feinteilige, in H₂O dispergierte PERCOLL-Partikel (PVP-umhüllte SiO₂-Teilchen mit=2,0 g/cm³ und 5dynamischer, radial ansteigender Dichtegradient aufgebaut, der quer durch die ganze Zelle wandert. Zu analysierende Mikropartikel sammeln sich in Banden innerhalb des H₂O/PERCOLL-Dichtegradienten an. Es werden die Grundlagen und der mathematische Auswerteformalismus der neuen Methode geschildert sowie ihre Grenzen aufgezeigt. Meßbeispiele an Polymerdispersionen, organischen Mikrokristallen und Bakterienzellen illustrieren die Anwendungsmöglichkeiten der Methode.

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The paper reports of a rapid analytical ultracentrifuge method which allows to fractionate microparticles with regard to their density and to estimate average densities or possible density distributions within the range of 0.85<<1.15 g/cm³. Thus information is obtained about the chemical composition and/or a possible chemical heterogeneity of the particles. In an ultracentrifuge cell a radially increasingdynamical density gradient is built up within 20 min by the sedimentating front of extremely small PERCOLL-particles (PVP-coated SiO₂-particles with=2.0 g/cm³ and 52O. The microparticles to be analyzed are collected and observed as turbidity bands in the H₂O/PERCOLL-density gradient. The physical and mathematical principles of the new method and its limits are shown. The applicability of the method is demonstrated by means of measurements on polymer dispersions, microcrystals and bacteria cells.

Herrn Dr. Dieter Heinze zum 60. Geburtstag gewidmet.     

Apparent molar heat capacities and volumes of electrolytes and ions int-butanol-water mixtures

The apparent molar volumes V and heat capacities C _p, of NaCl, LiCl, NaF, KI, NaBPh₄ and Ph₄PCl have been determined in solutions of H₂O containing up to 40 mass% t-butyl alcohol (TBA) by flow densitometry and flow microcalorimetry. Combination of these results with literature data allows calculation of V and C _p, for 16 ions in these mixtures using the assumption that _tX(Ph₄P⁺) = _tX(BPh ₄ ^– ) where X=V or C _p and _tX is the change in X for a species on transfer from H₂O to TBA-H₂O mixtures. These are the first reported single ion values for C _p, in a mixed solvent. While whole electrolyte volumes and heat capacities show relatively smooth changes with solvent composition, _tX(ion) exhibit two well-developed extrema at around 10 and 25 mass% TBA. The shape of the _tX(ion) curves shows considerable uniformity among the alkali metal cations and the halide ions but the extrema become more pronounced with increasing size among the tetraalkylammonium ions. These extrema are analogous to those observed in aqueous organic mixtures of surfactants and are probably indicative of microphase transitions in these strongly interacting solvent mixtures.     

Kinetics and mechanism of nucleophilic substitution of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II) by pyridine bases

The reaction of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II), Pd(RaaiMe)Cl₂ where RaaiMe = p-R–C₆H₄N=N–C₃H₂N₂-1-Me; R = H(1), Me(2), Cl(3), with pyridine bases [RPY: R = H (a), 4-Me (b), 4-Cl (c), 2-Me (d), 2,6-Me₂ (e), 2,4,6-Me₃ (f)] has been studied spectrophotometrically in MeCN at 451 nm. The products (4) have been isolated and characterised as trans-Pd(RPy)₂Cl₂. The kinetics of the nucleophilic substitution has been examined under pseudo-first-order conditions at 298 K. A single phase reaction step has been observed for bases such as Hpy (a), 4-MePy (b) and 4-ClPy (c) and follows the rate law: rate = (a + k[RPy]²[Pd(RaaiMe)Cl₂]). The bases 2-MePy (d), 2,6-Me₂Py (e) and 2,4,6-Me₃Py (f) exhibits a bi-phasic reaction and follows the rate laws: rate–1 = (a + k[RPy][Pd(RaaiMe)Cl₂]) and rate–2 = (a + k[RPy][Pd(RaaiMe)-Cl₂]), where k is the third-order rate constant; k is the second-order first phase rate constant, k is the second-order second phase rate constant and a/a/a correspond to the solvent dependent constant of the respective reaction path. The rate data supports a nucleophilic association path. External addition of Cl^– (LiCl) suppresses the rate, which follows the order: k/k/k (3) > k/k,k (1) > k/k,k (2). The k values are linearly related to the Hammett constants. The 2-substituted pyridines (d–f) remarkably reduce the rate and show a bi-phasic reaction behaviour as compared with 4-Rpy (a–c). This is attributed to the steric effect that destabilises the transition state. The rate decreases with increasing steric crowding at the ortho-position and follows the order: (d) > (f) > (e). The 4-substituted pyridines control the rate via an inductive effect and follow the order: (b) > (a) > (c).     

Bestimmung der molaren Masse und der Ladungszahl von Polymerelektrolyten mit der Ultrazentrifuge

Zusammenfassung In der vorliegenden Arbeit wird das Sedimentationsgleichgewicht der Systeme Na₆[H₂W₁₂O₄₀]—NaCI—H₂O und Na₆[H₂W₁₂O₄₀]—NaClO₄— H2O untersucht. Die scheinbare molare Masse Mapp des Natriummetawolframats wird in beiden Systemen als Funktion der Natriummetawolfrarnat-Anfangspartialdichte ₀ ^PX _z gemessen. Durch lineare Extrapolation der Funktion Mapp = Mapp (PP,, ) auf die Polymerelektrolyt-Anfangspartialdichte Null können die Grenzwerte der scheinbaren molaren Masse (Mapp)o ermittelt werden. Aus den (Mapp)o-Werten wird die Abhängigkeit der Größe (ln _PXz /m _BX ) _mPXz von der NaCI- bzw. NaClO₄-Molalität berechnet.Die Bestimmung der molaren Masse und der (stöchiometrischen) Ladungszahl eines Polymerelektrolyten aus den experimentell ermittelten (Mapp)o-Werten unter Anwendung der Lamm-Williams-Gleichung wird diskutiert. Zur Ermittlung der beiden Größen müssen mehrere Versuchsreihen mit zwei verschiedenen Fremdelektrolyten durchgeführt werden. Externe Messungen sind nicht erforderlich.Man erhält auf diese Weise verläßliche Werte so-wohl der molaren Masse als auch der (stächiometrischen) Ladungszahl.

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Summary The sedimentation equilibria of the systems sodium metatungstate-sodium chloride-water and sodium metatungstate-sodium perchlorate-water are investiated. In both systems the apparent molecular mass Mapp of sodium metatungstate (PX _z) is measured in dependence on partial density ₀ ^PX _z before centrifugation. By linear extrapolation of the function Mapp = Mapp ( ₀ ^PX _z the limiting value (Mapp)o for ₀ ^PX _z = 0 is obtained. The variation with sodium chloride and sodium perchlorate molality of the quantity (ln _{PX z} ^m _BX )mPX_z is calculated from (Mapp)o data.The determination of the molecular mass and the algebraic valency of a polymeric ion by means of the (Mapp)o values calculated by Lamm-Williams equation is discussed. In order to obtain these two quantities at least two series of experiments are required, each of which using a different supporting electrolyte. External measurements are not necessary. In this way reliable values for the molecular mass as well as for the stoichiometric valency are obtained.

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Mit 5 Abbildungen und 3 Tabellen     

Effect of thick fixed-charge layers on electrostatic interaction — a theoretical approach

The electrostatic interaction pressure of charged surface layers is considered qualitatively and quantitatively. In the case of mutual penetration of the surface layers in addition to Maxwell stress and osmotic resp. hydrostatic pressure an isotropic stress on the fixed charges carrying molecules of the surface layers has to be taken into account. The derivation of the pressure-distance equations is given starting from both thermodynamic/electrostatic and hydrostatic/electrostatic principles. A possible biological significance of the additional stress is discussed emphasizing its role in modifying the structure of surface layer molecules.List of symbols e ₀ elementary charge - k Boltzmann constant - n _i concentration of theith ionic species in the bulk solution - P hydrostatic pressure - P hydrostatic pressure in the bulk volume (× ) - P ^h integration constant, independent on ×:P ^h =P(h) - T absolute temperature - Z _i electrovalence of theith ionic species - thickness of the surface layer - , ₀ relative and absolute permittivities - II(×) osmotic pressure at position × - II osmotic pressure in the bulk solution (× ) - osmotic pressure in the symmetry plane of interacting identical surface layers (electric field strength equals zero) - integration constant, independent on ×: - _e ^h electrostatic component of the disjoining pressure _e ^h = _e (h) - (×) mobile charge density profile (cations and anions of the electrolyte) - (×) fixed charge density profile - ^t(x) total charge density profile ( ^t = +) - ¹(x) fixed charge density profile of one of the two surface layers ( ¹(×) 0 for 0×) - (×) electric potential profile     

Reaction between the OH group of hydroxyproline and diisocyanate catalyzed by an organotin compound

We have studied the kinetics of the reaction of L-hydroxyproline with OCH(CH₂)₆NCO, catalyzed by organotin, avoiding side reactions by protecting the other active hydrogens of the aminoacid, and comparing it with the MeOH/n-BuNCO system.

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L-- -OCN(CH₂)₆NCO, , . . - .