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Half a Century of Polystyrene—A Survey of the Chemistry and Physics of a Pioneering Material

Hermann Staudinger, the founder of polymer chemistry, would have been 100 years old this year. One of the key materials with which he elucidated the structure of high polymers was polystyrene.—Polystyrene, one of the most important thermoplastics, has now been manufactured industrially for some 50 years. Not only has it simplified our daily lives in a variety of ways, it has also been a model substance for the development and expansion of polymer chemistry and polymer physics, and it was the pioneering material for handling polymer solutions and melts. This article surveys the development and present state of knowledge of the polymerization of styrene and of the relationships between structure and properties.     

Antioxidant oligomeric proanthocyanidins from Cistus salvifolius

The purified proanthocyanidin oligomers of Cistus salvifolius herb extract accounted for 78% of the total proanthocyanidins and 73% of the total antioxidant activity of this extract. To elucidate the structure of the oligomer, it was depolymerized by acid catalysis in the presence of phloroglucinol. The structures of the resulting flavan-3-ols and phloroglucinol adducts were determined on the basis of 1D- and reverse 2D-NMR (HSQC, HMBC) experiments of their peracetylated derivatives, MALDI-TOF-MS and CD spectroscopy. These observations resulting from the degradation with phloroglucinol were confirmed by 13C NMR spectroscopy of the oligomer. The mean molecular weight of the higher oligomeric fraction was estimated to be 5-6 flavan-3-ol-units.     

Influence of chlorine substitution on the self-assembly of zinc phthalocyanine

The adsorption and ordering of zinc phthalocyanine (ZnPc) and octachloro zinc phthalocyanine (ZnPcCl(8)) on an Ag(111) surface is studied in situ by scanning tunneling microscopy under ultrahigh vacuum. Two-dimensional self-assembled supramolecular domains are observed for these two molecules. We show how substituting chlorine atoms for half of the peripheral hydrogen atoms on ZnPc influences the self-assembly mechanisms. While intermolecular interactions are dominated by van der Waals forces in ZnPc molecular networks, ZnPcCl(8) molecular packing undergoes a sequential phase evolution driven by the creation of C-Cl...H-C hydrogen bonds between adjacent molecules. At the end of this evolution, the final molecular assembly involves all possible hydrogen bonds. Our study also reveals the influence of molecule-substrate interactions through the presence of fault lines generating a stripe structure in the molecular film.     

Semiclassical theory of vibrational,rotational and translational energy exchange in collisions of polyatomic molecules

We derive a theory of inter- and intramolecular transfer of vibrational, rotational and translational energy in collisions of polyatomic molecules, in the case that only short range forces are important. Normal mode vibrations of molecules are treated quantum mechanically whereas translations and rotations are assumed to be classical degrees of freedom. We are able to show that, in case of short range forces, the energy exchange in binary collisions is essentially governed by an effective mass which is given by an algebraic function of the usual reduced mass and moments of inertia and depends also on the relative orientation of the two molecules. As an application of the theory, we calculated the probabilities for collision-induced 1 →0 transitions of the v ₃ mode in pure CH₃I, CH₃Br and CH₃Cl gases. The calculated values are close to the experimental vibrational deactivation probabilities.