Low temperature crystal and molecular structure of nitrobenzene

The crystal and molecular structure of nitrobenzene was determined at 103 K by X-ray diffraction, yieldingR=0.034 and a highly precise geometry of the molecule (esds of bond lengths 0.001 Å and bond angles 0.1°). The bond angles in the ring agree very well with additive scheme based on angular substituent parameters. X-X electron density maps support the view that the C-N bond does not exhibit-character, and, hence, the nitro group interacts with the ring mostly by inductive effects.     

Multicomponent analysis with a computerized flow injection system using LED photometric detection

An original computer-controlled solid-state photometer has been developed and its potential for simultaneous multicomponent flow-injection analysis of binary and ternary mixtures is demonstrated. The device is simple in construction. Its principle of operation is based on rapid sequential measurements of the absorbance of the complexes formed by the analytes with chromogenic reagents at the wavelengths corresponding to the emission maxima of three light emitting diodes (563, 580 and 638 nm).     

Stimuli-responsive surface crystallization of phospholipids from bimodal colloidal particles

These studies focus on the effect of phospholipids in the presence of ionic surfactants on the behavior of poly(methylmethactrylate/n-butyl acrylate) (p-MMA/nBA) colloidal particles during film formation. With the presence of two surfactants, it is possible to obtain particles that exhibit two distinct particle sizes. The presence of hydrogenated soybean phosphatidylcholine (HSPC) and sodium dioctyl sulfosuccinate (SDOSS), which stabilize these bimodal colloidal dispersions, has a significant effect on the mobility of individual components during coalescence. Specifically, the presence of HSPC inhibits migration of SDOSS to the film-air (F-A) interface. Furthermore, the presence of electrolyte species such as aqueous CaCl2 has a very pronounced effect on film formation. When the Ca2+/HSPC ratio is 0.1/1.0, SDOSS is released to the F-A interface during coalescence. At 2.0/1.0 Ca2+/HSPC, HSPC diffuses to the F-A interface and crystalline domains consisting of HSPC are formed. This stimuli-responsive behavior is confirmed using IRIR imaging that ultimately exhibits different surface morphologies. These studies illustrate for the first time that it is possible to control the release of two different surface-active species during coalescence that form crystalline domains.     

Asymmetric allylic alkylation of ketone enolates: an asymmetric Claisen surrogate

[reaction: see text] The combination of catalytic palladium(0) and Trost ligand provides an effective catalyst for the rearrangement of allyl beta-ketoesters. The mechanism of the transformation involves formation of pi-allyl palladium intermediates which undergo enantioselective attack by ketone enolates. Decarboxylation of beta-ketocarboxylates allows regiospecific generation of enolates under extremely mild conditions.     

Electronic spectrum of dibiphenylene-ethene radical anion

The electronic absorption spectrum for the dibiphenylene-ethene radical anion ( ), generated electrochemically in dimethylsulfoxide solutions, is reported. Based on calculations by the LCAO-MO method in theHückel approximation and on the analysis of the band positions it is suggested that in the molecule two planar fluorenylidene fragments are twisted (60°) about the central C=C bond.

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Das Elektronenabsorptionsspektrum des Dibiphenylen-Radikalanions (Kurze Mitteilung)

Zusammenfassung Das Dibiphenylenethen-Radikalanion ( ) wurde elektrochemisch hergestellt und das Elektronenabsorptionsspektrum aufgenommen. Auf Grund von LCAO-MO Berechnungen in derHückel-Annäherung und der Analyse der Bandenlagen wird nahegelegt, daß im -Molekül zwei planare Fluorenyliden-Fragmente ca. 60° um die zentrale C=C-Bindung verdrillt angeordnet sind.

     

Stability of workroom air volatile organic compounds on solid adsorbents for thermal desorption gas chromatography

The storage stability of the occupationally frequently occurring compounds, methylethylketone, methylisobutylketone, benzene, toluene, tetrachloroethylene, n-butylacetate, -pinene, β-pinene, limonene and n-decane, has been investigated on the adsorbents Tenax TA, Chromosorb 106 and Carbotrap using thermally desorbable tube type samplers, commonly utilized in ambient and workroom atmospheric measurements. Fifty and 500 ng of each compound were loaded on the various adsorbents tubes, stored at both ambient (20 °C) and refrigerated (4 °C) temperatures and analysed by means of thermal gas chromatography with mass spectrometric detection on days 0, 7, 14 and 28 after exposure. A 90% storage recovery was chosen as acceptance criteria for storage stability, and statistical testing by Student's t-test, analysis of variance and Bonferroni post hoc tests were employed to investigate the effect of the categorical variables storage time, storage temperature and analyte loading on the different adsorbents. Chromosorb 106 showed the overall best behaviour with recoveries of 90% or better for all analytes during the 28-day test period. Tenax TA and Carbotrap yielded lower recoveries and were more influenced by variations in storage time, storage temperature and analyte loading. Refrigerated temperatures were best avoided for storage on Tenax TA, but may increase the recovery of some compounds on Carbotrap (e.g. n-butylacetate). The blank build-up on the adsorbents was also investigated, and Carbotrap and Tenax TA showed no signs of artefact development over time. Chromosorb 106, however, contained inherently more artefacts that build up over time, which in spite of the excellent storage capability, may limit its use in field studies where long storage times are normal.     

Gilmaniellin and Dechlorogilmaniellin,Two Novel Dimeric Oxaphenalenones

The structure and configuration of gilmaniellin, a metabolite of Gilmaniella humicola BARRON , has been shown to be 2 by X-ray analysis. By comparison of spectral data structure 1 has been assigned to dechlorogilmaniellin.     

Photoinitiation by radical-cationic mechanism in the polymerization of isobutylene with lewis acids

ESR spectra of Lewis acids (VCl₄, TiCl₄, TiBr₄, SnCl₄, and AlBr₃) and their mixtures with isobutylene were investigated in a n-heptane solution in the dark and under irradiation at 400–480 nm at ?80 to ?150°C. A signal was observed only upon irradiating mixtures of VCl₄, TiCl₄, or TiBr₄ and isobutylene. The signal was identified as an isobutylene radical-cation by comparison with a simulated spectrum. A signal indicating the presence of peroxy radicals were recorded in measurements carried out in the presence of oxygen; these radicals originated from reaction of the isobutylene radical-cation with oxygen. Radical-cation initiation by visible light is indicated by the polymerization of isobutylene by VCl₄, TiCl₄, and TiBr₄ and by ESR spectra. The inhibiting effect of oxygen in photochemically initiated polymerization of isobutylene was also elucidated.     

Transient Radicals Formed by Electron Transfer between inorganic ions and excited aromatic molecules in polar solvents

Fluorescence quenching of aromatic molecules by inorganic anions has been the subject of many investigations, yet the nature of the quenching mechanism is not fully understood. The fluorescence-quenching rate constants correlate with electrochemical data, but the radicals expected to form upon transfer of an electron to the excited aromatic molecules have escaped observation. We report the first observation of radical-ion species formed by electron-transfer quenching with inorganic anions in acetonitrile. A decisive step leading to formation of separated radical ions is the trapping of the primary charge-transfer complex by a second inorganic ion.