Aminyloxide (nitroxide)-XXVI: ESR-spektroskopische untersuchung von hydrazonyloxiden. Ermittlung der spindichteverteilung

The so-called “Bergmann oxide” 4a and the related compounds 4b-i dissociate reversibly to the corresponding radicals 5 at elevated temperatures. Analysis of the ESR spectra reveals that in 5a-f the unpaired electron is delocalized over the entire molecule. On the other hand the strongly reduced spin density at the β-carbon atom in 5h-i as well as in 7 indicates a twisting about the N,N-bond in these radicals, whereas m 5g the bond between the β-carbon atom and the group Ar¹ is twisted. The results of spin density calculations for radicals 5 are in agreement with the experimentally estimated spin densities. In spin trap experiments with nitrosobenzene or nitrones respectively, 5a reacts at the β-carbon atom, indicating this position as the most reactive one.     

Propriétés des copolymères biséquencés polyoxyéthylène-polystyrène

Résumé On a préparé des monocristaux de copolymères biséquencés polyoxyéthylène-polystyrène (POE-PS) à partir de leurs solutions diluées, qui peuvent contenir jusqu'à 55% de PS. Les principales formes de ces cristaux et leurs variantes morphologiques, observées sous microscope optique, sont décrites et rattachées à la maille cristallographique du POE. On présente aussi quelques exemples de monocristaux obtenus par ensemencement, dans lesquels les différentes formes se succèdent par filiation; on discute les transitions des formes et leur dépendance vis à vis des conditions de cristallisation.La cristallisation de ces copolymères provoque généralement un fractionnement en composition, car la proportion de PS dans les cristaux est limitée. On propose deux modèles de structure différents, dans lesquels une ou deux couches cristallines de POE en configuration repliée sont recouvertes par le PS amorphe. Le processus de fractionnement est interprété à partir de ces deux structures en admettant une extension critique pour les séquences de PS, dont l'une des extrémités est ancrée sur la surface des repliements du POE.

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Summary Single crystals of copolymers, composed of one Poly(ethylene-oxide), (POE), and one Polystyrene (PS) block, (which may contain 55% of PS, by weight), have been prepared from dilute solutions. The principal crystal habits and their morphological variations, as observed with an optical microscope, are described and related to the unit cell of POE. Single crystals grown from various types of seeds, in which different external habits succeed one another, are also shown. Transitions of crystal habits and their dependence on crystallisation conditions are discussed in some detail.Generally, crystallisation of these copolymers produces some fractionation with respect to composition, for only a limited fraction of the initial PS can enter into the crystal. Two different crystal structures are proposed in which a single, or a double crystalline layer of folded POE is covered by amorphous PS. The fractionation process is interpreted on the basis of these two structural models, assuming a critical extension of the PS blocks anchored at one end to the fold surface of PEO.

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Zusammenfassung Einkristalle von Copolymeren aus einem Polyäthylenoxyd (PEO) und Polystyrol (PS)-Block, die gewichtsmäßig 55% PS enthalten können, wurden aus verdünnten Lösungen präpariert. Der grundsätzliche Charakter der Kristalle und ihre morphologischen Variationen, wie es in einem optischen Mikroskop beobachtet wird, ist beschrieben und mit der Elementarzelle PEO in Beziehung gebracht. Einkristalle, entstanden aus verschiedenen Typen von Kristallkeimen, in welchen verschiedene äußere Formen auftreten, die aufeinanderfolgen, werden gezeigt. Die übrigen Kristallformen und ihre Abhängigkeit von den Kristallisationsbedingungen werden im einzelnen diskutiert.Im allgemeinen verursacht die Kristallisation dieser Copolymeren gewisse Fraktionierung hinsichtlich der Zusammensetzung, da nur eine begrenzte Menge des ursprünglichen Polystyrols in den Kristall eintreten kann. Zwei verschiedene Kristall-Strukturen werden vorgeschlagen, in denen bzw. eine oder zwei Schichten von gefaltetem PEO mit amorphem Polystyrol bedeckt ist. Der Fraktionierungsprozeß wird auf Grund dieser zwei Struktur-Modelle interpretiert, die eine kritische Größe der PS-Blöcke, verankert an einem Ende der gefalteten Oberfläche von PEO, annehmen.

     

13C-ESR-Kopplungskonstanten des radikalanions des 3,5-di-tert-butyl-nitrobenzols

¹³C-ESR coupling constants of all ring carbon atoms of the radical anion of 3,5-di-tert-butyl-nitrobenzene are determined on samples with ¹³C in natural abundance and assigned on the basis of their solvent dependence. The assignment of a ¹³C coupling constant described for the radical anion of nitrobenzene is revised.     

Neutral-pion photoproduction off protons in the energy range 0.3 GeV<E(gamma)<3 GeV

Single pi(0) photoproduction has been studied with the CB-ELSA experiment at Bonn using tagged photon energies between 0.3 and 3.0 GeV. The experimental setup covers a very large solid angle of approximately 98% of 4pi. Differential cross sections dsigma/dOmega have been measured. Complicated structures in the angular distributions indicate a variety of different resonances being produced in the s channel intermediate state gammap-->N(*)(Delta(*))-->ppi(0). A combined analysis including the data presented in this letter along with other data sets reveals contributions from known resonances and evidence for a new resonance N(2070)D15.     

Epitaxy of helical polyolefins

The structural rules which govern the epitaxial crystallisation of polymers - and especially polyolefins - on organic substrates are established. Illustrative examples involve isotactic and syndiotactic polypropylenes and poly( l-butene). Investigation of the film structure by electron microscopy, electron diffraction and atomic force microscopy reveals some unprecedented features, including in particular the selection of the contact plane according to the chirality of its constituent helices, and direct observation of both right and left hands of polyolefin helices.     

Rhenium ethoxy- and hydroxycarbene complexes with thiophene substituents

Reaction of mono- and dilithiated thiophene (a), bithiophene (b) and 2,5-dibromothiophene (c) with [Re(2)(CO)(10)] afforded, after subsequent alkylation with triethyloxonium tetrafluoroborate, tetra- and binuclear Fischer carbene complexes, [Re(2)(CO)(9){C(OEt){C(4)H(2)S}(n)X}], n = 1, X = H (1a); n = 2, X = H (1b); n = 1, X = Br (1c); n = 1, X = C(OEt)Re(2)(CO)(9), (2a); n = 2, X = C(OEt)Re(2)(CO)(9) (2b), as major products. The dirhenium acylate intermediates from this reaction not only gave the expected novel ethoxycarbene complexes with alkylation but after rhenium-rhenium bond breaking afforded a number of minor products. The (1)H NMR spectrum of the crude reaction mixture revealed the formation of four metal hydride complexes and aldehydes. Protonation with HBF(4) instead of alkylation with Et(3)OBF(4) significantly increased the yields of the hydride complexes, which enabled the positive identification of three of these complexes. In addition to the known compounds [Re(CO)(5)H] and [Re(3)(CO)(14)H] (3), a unique complex displaying a hydroxycarbene fragment connected to an acyl fragment via an O-H···O hydrogen bond and a Re···H···Re bond linking the two Re centers, [(μ-H){Re(CO)(4)C(OH){C(4)H(2)S}(n)H}{Re(CO)(4)C(O){C(4)H(2)S}(n)H}], n = 1 (4a) or n = 2 (4b), were isolated. The formation of thiophene aldehydes, H{C(O)}(m){C(4)H(2)S}(n)C(O)H (m = 0 or 1 and n = 1 or 2), were observed and the novel monocarbene complexes with terminal aldehyde groups, [Re(2)(CO)(9){C(OEt){C(4)H(2)S}(n)C(O)H}], n = 1 (5a) and n = 2 (5b) could be isolated. A higher yield of 5b was obtained after stirring crystals of 2b in wet THF. The crystal structures of 1a, 2a, 4a and 5b are reported.     

Intercalation of Benzamide into Kaolinite

Well-crystallized kaolinite (K) was initially reacted at 60 degrees C with a water/dimethylsulfoxide (DMSO) mixture and the resulting intercalation derivative (K-DMSO) was characterized by powder X-ray diffractometry (PXRD), thermal analysis (simultaneous TG and DSC), and Fourier-transformed infrared spectroscopy (FTIR). Benzamide crystals were then melted with the K-DMSO derivative at 140 degrees C for 4 days, when a gradual displacement of DMSO by benzamide was observed within the interlayer spacing of the modified kaolinite. The resulting material, after extensive washing with acetone, was characterized and compared to the results obtained previously for the K-DMSO composite. Benzamide intercalation proceeded by gradual displacement of DMSO molecules until completion. The structural stabilization of the K-BZ derivative was explained through the establishment of hydrogen bonds between the carbonyl oxygen atoms of the intercalated benzamide and aluminol groups present at the surface of the kaolinite layer. The interlamellar spacing of K-BZ was shown to be possibly occupied by benzamide molecules that were located at a 68 degrees orientation in relation to the layer surface. Unlike most intercalation molecules such as DMSO, variations in the interplanar spacing of kaolinite were consistent with the nonkeying of any other part of the molecule between the aluminosilicate interlayers. Copyright 2000 Academic Press.     

The synthesis,characterization and melting properties of thiophene-containing dithiocarboxylate complexes of nickel(II)

The reactions of a series of 5-alkyl-2-thiophenedithiocarboxylates with nickel(II) chloride afforded two types of complexes, blue nickel(II) complexes with two terminal dithiocarboxylate ligands, [Ni(S₂CTR)₂] and violet nickel(II) complexes with perthio- and dithiocarboxylate ligands, [Ni(S₂CTR)(S₃CTR)] (where T = 2,5-disubstituted thiophene, R = C_nH_2n+1, n = 4, 6, 8, 12, 16). The blue monomers are preferred for the shorter chains (C₄ and C₆) and the violet compounds form exclusively for the longer chains (C₈, C₁₂, and C₁₆) in the alkylthiophene complexes. In addition to the above series, [Ni(S₂CTCH₃)₂], was prepared in a one-pot reaction in THF and both the blue and violet products were isolated. It was possible to convert the blue complexes [Ni(S₂CTR)₂] (R = butyl, hexyl) into the corresponding violet complexes [Ni(S₂CTR)(S₃CTR)] after stirring in THF solutions for prolonged periods of time. Liquid-crystalline properties of these complexes were examined by DSC and POM. The violet complexes with C₈ and C₁₂ alkyl chains showed liquid-crystalline properties.     

Über Chalkogenolate. 163. Umsetzungen von Hydrazin mit Kohlenstoffdisulfid. 2. Kristallstruktur von Dikalium-1,2-hydrazin-bis(dithioformiat)

On Chalcogenolates. 163. Reactions of Hydrazine with Carbon Disulfide. 2. Crystal Structure of Dipotassium 1,2-Hydrazine-bis (dithioformate) The title compound K₂[S₂C? NH? NH? CS₂] ( 1 ) crystallizes with Z = 4 in the orthorhombic space group Pbna with cell dimensions a = 6.635(1), b = 10.825(2), c = 12.866(2) Å. The crystal structure has been determined from single crystal X-ray data measured at ?85 °C and refined to a conventional R of 0.034 for 969 independent reflections (R_w = 0.042). The [S₂C? NH? NH? CS₂]^2? ions are linked together by hydrogen bridges N? H…?S. The K⁺ ions are surrounded by seven sulfur atoms in irregular coordination.