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81.
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Harry Dickerson Steven Ferber Frederick S. Richardson 《Theoretical chemistry accounts》1976,42(4):333-344
The chiroptical properties associated with the * transitions in dissymmetric allene systems are calculated and relationships between the chiroptical observables and the stereochemical and electronic structural features of these systems are examined. The calculations are based on the INDO and CNDO/S semiempirical molecular orbital models for the electronic structure of the molecular systems and excited states are constructed in the virtual orbital-configuration interaction approximation. The dipole strengths, rotatory strengths, and dissymmetry factors for the three lowest energy * transitions are computed and reported for eleven chiral allene structures. Relationships between absolute configuration and the signs of the * rotatory strengths are examined and discussed. 相似文献
85.
Dussault PH Lee IQ Lee HJ Lee RJ Niu QJ Schultz JA Zope UR 《The Journal of organic chemistry》2000,65(25):8407-8414
The Lewis acid-mediated reaction of alkene nucleophiles with peroxyacetals provides an effective route for the synthesis of homologated peroxides and hydroperoxides. In the presence of Lewis acids such as TiCl(4), SnCl(4), and trimethylsilyl triflate, peroxyacetals and peroxyketals undergo reaction with allyltrimethylsilane, silyl enol ethers, and silyl ketene acetals to afford homoallyl peroxides, 3-peroxyketones, and 3-peroxyalkanoates, respectively. Reactions of peroxyacetals are Lewis acid dependent; TiCl(4) promotes formation of ethers while SnCl(4) and trimethylsilyl triflate promote formation of peroxides. Lewis acid-promoted reactions of silylated hydroperoxyacetals furnish silylated hydroperoxides, which can be deprotected to homologated hydroperoxides. Hydroperoxyketals undergo Lewis acid-mediated allylation to furnish 1,2-dioxolanes via attack of hydroperoxide on the intermediate carbocation. Lewis acid-mediated cyclization of unsaturated peroxyacetals furnishes 1,2-dioxanes, 1,2-dioxepanes, and 1,2-dioxacanes through 6-endo/exo, 7-endo/endo, and 8-endo/endo pathways. The corresponding reactions involving 6-endo/endo and 5-endo/exo pathways were unsuccessful. 相似文献
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Stefaniak AB Brink CA Dickerson RM Day GA Brisson MJ Hoover MD Scripsick RC 《Analytical and bioanalytical chemistry》2007,387(7):2411-2417
Complete digestion of all chemical forms and sizes of particulate analytes in environmental samples is usually necessary to
obtain accurate results with atomic spectroscopy. In the current study, we investigate the physicochemical properties of beryllium
particles likely to be encountered in samples collected from different occupational environments and present a hypothesis
that a dissolution theory can be used as a conceptual framework to guide development of strategies for digestion procedures.
For monodisperse single-chemical constituent primary particles, such as those encountered when handling some types of beryllium
oxide (BeO) powder, theory predicts that a digestion procedure is sufficient when it completely dissolves all primary particles,
independent of cluster size. For polydisperse single-chemical constituent particles, such as those encountered during the
handling of some types of beryllium metal powder, theory predicts that a digestion procedure is sufficient only when it completely
dissolves the largest particle in the sample. For samples with unknown or multi-chemical constituent particles and with particles
having undefined sizes, e.g., fume emissions from a copper–beryllium alloy furnace operation or dust from a beryl ore crushing
operation, a surface area-limited and single-constituent-dependent dissolution theory may not predict complete dissolution,
thereby requiring non-routine robust treatment procedures with post-digestion filtration, followed by examination of residual
particulate material. Additionally, for beryllium, and likely other poorly soluble materials, particulate reference materials
of various chemical forms and size distributions are needed to better evaluate and harmonize analytical digestion procedures.
Figure Generation of aerosol particles during machining of beryllium oxide
The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National
Institute for Occupational Safety and Health. 相似文献
89.
Nornicotine, a native component of tobacco and minor nicotine metabolite, was found to catalyze the chemoselective reduction of alpha,beta-unsaturated aldehydes under homogeneous aqueous conditions. 相似文献
90.
On the structure and chemistry of complex oxide nanofeatures in nanostructured ferritic alloy U14YWT
D. Bhattacharyya P. Dickerson G.R. Odette S.A. Maloy A. Misra M.A. Nastasi 《哲学杂志》2013,93(16):2089-2107
The remarkable radiation damage resistance of nanostructured ferritic alloys (NFAs) is attributed to the large numbers of matrix nanofeatures (NFs) of various types, which can enhance the recombination of displacement defects and trap transmutant helium in fine scale bubbles. Characterizing the chemistry, crystallographic structure and orientation relationships of the NFs is critical to understanding how they enhance the radiation damage resistance of NFAs. Conventional and high-resolution transmission electron microscopy and energy-dispersive spectroscopy were used to characterize the various types of NF and larger oxide phases in a model 14Cr–3?W–0.4Ti–0.25Y2O3 NFA (14YWT) hot isostatic pressed (HIP-ed) at 1150°C. Large CrTiO3 precipitates (50–300?nm) and small diffracting NFs (<5?nm) were found in this alloy. One major new result is the observation of an additional type of nanofeature (10–50?nm), orthorhombic in structure, with a square center cross-section, which constitutes a new kind of Y–Ti-oxide phase with lattice parameters different from those of known Y and Ti complex oxides. The interfaces of these particles seem to be semicoherent, while manifesting a possible orientation relationship with the BCC matrix. The ratio of Y to Ti varies between <1 and 2 for these larger NFs. 相似文献