Magnetic circular dichroism spectra of triphenylene and coronene

The absorption spectra of triphenylene (I) and coronene (II) are assigned by using the MCD spectra and the results of the SCF screened potential π-MO CI calculations. The calculated Faraday A/D values for the ¹E and ¹E_1u excited states of I and II are in excellent agreement with the experimental values, in contrast to the calculated Faraday B value for the ¹E_1u state of II.     

Verwendung des Absorptionseffektes der Elektronen- und R?ntgenstrahlen zur qualitativen und quantitativen Analyse

Zusammenfassung Die Beobachtung des Absorptionseffektes bei der Elektronenbeugung und Röntgenstrahlenmikroskopie kann sowohl zur qualitativen als auch zur quantitativen Analyse eines wirksamen Gemenges dienen.     

Eine Methode zur quantitativen Bestimmung der ferro-magnetischen Beimengungen im austenitischen Stahl mit Hilfe der Elektronenbeugung

Zusammenfassung Der magnetische Lorentz-Effekt, der bei der Elektronenbeugung an einem Ferromagneticum erscheint, kann zur Analyse der ferromagnetischen Beimengungen im 18-8-Stahl dienen. Diese Beimengungen erfaßt man nach dem vorliegenden Verfahren sowohl magnetisch als auch kristallographisch.     

Marked effect of aromatic solvent on unfolding rate of helical ethynylhelicene oligomer

Optically active acyclic ethynylhelicene oligomers were synthesized in high yields by a two-directional method involving Sonogashira coupling and deprotection. Their CD spectra in chloroform exhibited large differences between the oligomers with less than seven helicenes and their higher homologues, which indicated the formation of helical structures for the latter and random coil structures for the former. The helical heptamer gradually unfolded to a random coil structure in chloroform at room temperature. The unfolding rate was examined by CD in several aromatic solvents as well, and the rate constant k was found to be highly dependent on the type of aromatic substituent: k differed by seven orders of magnitude between iodobenzene and trifluoromethylbenzene. Several features of the rates are notable: The reaction rates in halobenzenes were in the order of iodobenzene > bromobenzene > chlorobenzene > benzene > fluorobenzene > m-difluorobenzene, those in alkylbenzenes were styrene > phenylacetylene > ethylbenzene > toluene > benzene, and those in heteroatom-substituted arenes were thioanisole > benzonitrile > anisole > ethyl benzoate > benzene > trifluoromethylbenzene. The log k values exhibited good correlation with the absolute hardness, eta, of the arenes, and higher unfolding rates were observed in the soft arenes. Vapor pressure osmometry studies indicated that the helical structure of the heptamer is dimeric in benzene, fluorobenzene, and trifluoromethylbenzene, while the random coil structure of the heptamer is monomeric in chloroform and toluene. When a chloroform solution of the random coil structure was concentrated to a small volume, the helical structure could be regenerated.     

Versatile formation of [2]catenane and [2]pseudorotaxane structures; threading and noncovalent stoppering by a self-assembled macrocycle

A self-assembled dimeric macrocycle between 4,4'-bis(4-pyridylmethoxy)biphenyl (L) and (en)Pd(NO(3))(2) was constructed, and its interactions with cyclodextrins of different cavity size resulted in the formation of [2]catenane and [2]pseudorotaxane systems, respectively. The structures were identified by 1D and 2D NMR spectroscopy and cold spray ionization mass (CSI-MS) spectrometry.     

Reaction-phase-selective inter- and intramolecular photochemical reaction of 2-pyridone derivatives

Phase-selective photochemical reaction of 2-pyridone derivatives was examined. Irradiation of 1 in benzene mainly gave rearrangement products 2. However, intermolecular [4 + 4] photocycloaddition proceeded quantitatively in the solid state, affording photodimers 3. An effective pi-pi stacking and dipole-dipole interaction between two pyridone moieties might play important roles in an effective arrangement of 1 for photodimerization in their crystal structures. [reaction: see text]     

Three-dimensional observation of an helical hot structure during a sawtooth crash in the WT-3 tokamak

Sawtooth crashes in an Ohmically heated plasma in the WT-3 tokamak have been observed by using soft x-ray computer tomography at three different poloidal cross sections around the torus. Initially, collapsing proceeds slowly with keeping the helical structure of an m = 1/n = 1 hot core around the torus. It accelerates as the helical hot structure is strongly deformed and fades away in the manner that the hot core at the high field side becomes obscure and disappears, while that at the low field side is deformed into a thin crescent aligned along the inversion circle, which survives even at the completion of the crash.