Die Ringinversions-Barriere in [2.2]Metacyclophan

From racemization studies on optically active [2.2]metacyclophanes substituted in position 4, the parameters of activation for the inversion of the tenmembered ring were found to be: G ₄₂₃ =31.5 kcal/mole, H =27.5 kcal/mole and S =–10 Cl/mole.Racemization does not occurvia bond forming or breaking; the value for the inversion barrier is not affected by substituents in position 4 and therefore corresponds to the value of unsubstituted [2.2]metacyclophane, whereas substituents in the bridge exert a distinct influence. These results can easily be explained on the basis of the isoconformational concept.

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Mit 5 Abbildungen

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Herrn Prof. Dr.O. Hoffmann-Ostenhof mit besten Wünschen zum 60. Geburtstag gewidmet.     

Grain boundary relaxation phenomena in block and graft copolymers

Summary The grain boundary relaxation phenomena, which have been found in the mechanical relaxation of the cast films of a series ofgraft copolymers ofpoly(methyl acrylate) with styrene, are examined again, in order to understand its relaxation mechanism, by using some particular series of heterogeneous systems of two components having different interaction between the two phases and, subsequently, different grain boundary structure; i. e., two series of poly(vinyl acetate) filled with two types of carbon blacks having relatively high and low surface activities, respectively, a series ofmechanical mixtures ofpoly(vinyl acetate) with polystyrene, and a series of styrene-isoprene-styrene tri-block copolymers.The grain boundary relaxation phenomena are again detected for the series of the tri-block copolymers but definitely not for the series of the mechanical mixtures, suggesting that the grain boundary relaxation phenomena must arise not from the heterogeneous structures themselves but from characteristic arrangements of molecular chains at the boundary of the two phases. That is, there must be a considerably strong interaction between the two phases, and there exists an intermediate phase in which the polymer segments of soft component are rigidified while the other polymer segments of hard component are softened. In other words, there must be a cooperative motions of chain segments of the two components to produce a mechanical relaxation under a certain environmental condition, such as temperature and time scale of observation.

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Zusammenfassung Die Korngrenzenrelaxationsphänomene, die in der mechanischen Relaxation einer Serie von aus Graft-Copolymeren von Polymethylacrylat mit Styrol gefunden wurden, wurden erneut geprüft, um den Relaxations-mechanismus zu verstehen, unter Verwendung einer besonderen Serie von heterogenen Systemen zweier Komponenten, die verschiedene Wechselwirkungen zwischen den zwie Phasen besitzen und deshalb verschiedene Korgrenzenstrukturen. Das heißt, wir verwendeten zwei Serien von Polyvinylacetaten, gefüllt mit zwei Rußtypen von vergleichsweise hoher und niedriger Oberflächenaktivität, eine Serie von mechanischen Mischungen aus Polyvinylacetat mit Polystyrol und eine Serie von Styrol-Isopren-Dreiblockcopolymeren. Die Korngrenzenrelaxationsphänomene, wurden für die Serie der Dreiblockcopolymeren wiederum festgestellt, aber definitiv nicht für die Serie der mechanischen Mischungen. Das läßt vermuten, daß Korngrenzenrelaxation nicht von heterogenen Strukturen selbst, sondern von charakteristischen Anordnungen der molekularen Kette an der Grenze von zwei Phasen herrührt. Das heißt, es muß eine beträchtlich strenge Wechselwirkung zwischen den zwei Phasen bestehen, und es muß eine Zwischenphase existieren, in welcher die Polymersegmente der weichen Komponente versteift werden, während die anderen Polymersegmente der harten Komponente erweicht werden. Mit anderen Worten, es müssen cooperative Bewegungen von Kettensegmenten der zwei Komponenten vorhanden sein, um eine mechannische Relaxation unter gewissen Umgebungsbedingungenzuerzeugen, Umgebungsbedingungen wie Temperatur und Zeitskala der Beobachtungen.

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With 6 figures and 13 tables

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Presented at the 20th Annual Symposium on Rheology, Japan, Fukui, Oct. 18, 1972.     

Ein Verfahren zur Berechnung der Dampfzusammensetzung von ternären flüssigen Systemen

A simple method for calculating the vapor composition in ternary liquid systems is described and experimentally verified. Starting from the differential equation derived for curves of constant relative fugacity of two components (_ik=const) a relation is derived for the estimation of these curves in the concentration triangle. The _ik-values are determined as the finite points of curves _ik=const from the data of the vapor-liquid composition of the binary systems.

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Mit 3 Abbildungen     

Die Kristallstruktur von Ru2Si3

The crystal structure of Ru₂Si₃ has been refined by leastsquares using three-dimensional X-ray data from a twinned crystal (1355 reflections,R=5.8%). Ru₂Si₃ is isostructural with Ru₂Ge₃ and like this compound a member of the Mn₁₁Si₁₉ structure family. The lattice parameters of the orthorhombic unit cell (Pnca—D ₁₄ ^2h ) are:a=5.530 (1),b=11.060 (2) andc=8.952 (2) Å.

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Mit 1 Abbildung     

The surface activity of the lower homologues of n-alkylammonium chlorides in aqueous solutions. Effect of hydrophobic hydration

Summary The surface tensions of aqueous solutions ofn-alkylammonium chlorides (methyl to hexyl) have been measured at 25 °C. With methylammonium chloride the surface tension increased with concentration, whereas with ethylammonium chloride and higher homologues, the surface tension decreased with concentration. The results suggest that this transition is attributed to the effect of hydrophobic hydration. For propylammonium chloride and higher homologues, the relation between the surface tension lowering da and the concentrationC in the range of 0–10 dyne/cm, can be expressed by the equation; = AC + BC, whereA andB are constants. The surface tension coefficientB has been found to increase approximately twofold for each additional CH₂ group of alkyl chain.

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Zusammenfassung Es wurden die Oberflächenspannungen wäßriger Lösungen vonn-Alkylammoniumchloriden (Methyl- bis Hexylammoniumchloride) bei 25 °C gemessen. Für Methylammoniumchlorid nimmt die Oberflächenspannung mit der Konzentration zu, aber bei allen höheren Homologen mit der Konzentration ab. Die Ergebnisse deuten darauf hin, daß dieser Übergang durch die hydrophobe Hydration bedingt wird. Für Propylammonium-chlorid und die höheren Homologen wird die Beziehung zwischen der Erniedrigung der Oberflächenspannung und der KonzentrationC in dem Bereich von 1 bis 10 dyn/cm durch die folgende Gleichung ausgedrückt: = AC + BC (A undB sind Konstanten). Es wurde gefunden, daß B für jede zusätzliche CH₂-Gruppe etwa um den Faktor 2 größer wird.

     

Über das Bergapten

Ohne Zusammenfassung     

Die Hydrohalogenierung von Hexaphenyldigerman und die Schwingungsspektren einiger Ge2(C6H5) n X6−n -Verbindungen

The reactions of Ge₂(C₆H₅)₆ with HCl and HBr lead in nearly quantitative yields to the 1,1,2,2-tetrahalo derivatives Cl₂(C₆H₅)GeGe(C₆H₅)Cl₂ (I) and Br₂(C₆H₅)GeGe(C₆H₅)Br₂ (II), resp. The Si?Ge bond of (C₆H₅)₃SiGe(C₆H₅)₃ is cleaved under the conditions of hydrohalogenation. The vibrational spectra of Ge₂Br₆, Ge₂(C₆H₅)₆, I, and II are reported. The influence of vibrational coupling on ν GeGe in these compounds is discussed in detail, including vibrational calculations.     

Beiträge zur chemie der Pyrrolpigmente, 10. Mitt.: Elektronenspektrometrische Untersuchungen über die Struktur von Quadratsäurederivaten

The structure of squaric acid derivatives was investigated on the basis of the PPP—SCF—LCAO—MO—CI method utilizing the π-electron densities and bond orders. The parameters used in the calculations were modified to fit the experimental data for representative compounds. The data were obtained by X-ray photoelectron spectrometry and electron absorption spectroscopy (including the polarization of the bands as determined by liquid crystal induced circular dichroism measurements).     

N-Monobromamide: Darstellung durch Bromierung mit „Dibromisocyanursäure”, Eigenschaften

By reaction of primary carboxamides with “dibromoisocyanuric acid” (DBI) N-monobromoamides can be readily obtained as well as the N,N-dibromoamides described in an earlier paper¹. Reactions, some of them new, and properties of these compounds are described and compared with those of the N,N-dibromoamides. Like other compounds bearing the NHBr group^{2, 3} the N-monobromocarboxamides disproportionate at room temperature according to: 2 RCONHBr ? ? RCONH₂+RCONBr₂. For CH₃CONHBr the equilibrium constant was found to beK=0.02. In aqueous solution they behave as weak acids. The dissociation constants of eight compounds [R=?CH₃, ?C₂H₅, ?CH₂Cl, ?CHCl₂, ?CCl₃, ?CF₃, ?C(CH₃)₃ and ?C₆H₅] were measured: they differ from those of the corresponding carboxylic acids by about three powers of ten.