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101.
[reaction: see text] The influence of lithium ions on the conjugate addition of the monoorganocuprate reagent, Li[BuCuI], to a chiral crotonate has been investigated. The results show that iodotrimethylsilane (TMSI) is crucial for the asymmetric conjugate addition of the copper reagent, but only in THF or when 12-crown-4 is used. The reaction is thought not to involve any halosilane in any critical steps in the organocopper mechanisms conducted in Et(2)O. 相似文献
102.
Jesse I. Deutsch 《Archiv der Mathematik》2008,91(1):44-48
In a paper of Kim, Chan, and Rhagavan, the universal ternary classical quadratic forms over quadratic fields of positive discriminant
were discovered. Here a proof of the universality of some of these quadratic forms is given using a technique of Liouville.
Another quadratic form over the field of discriminant 8 is shown universal by a different elementary approach.
Received: 30 October 2007 相似文献
103.
Thiophene‐S,S‐dioxidized Indophenine: A Quinoid‐Type Building Block with High Electron Affinity for Constructing n‐Type Polymer Semiconductors with Narrow Band Gaps 下载免费PDF全文
Dr. Yunfeng Deng Bin Sun Yinghui He Jesse Quinn Dr. Chang Guo Prof. Dr. Yuning Li 《Angewandte Chemie (International ed. in English)》2016,55(10):3459-3462
Three thiophene‐S,S‐dioxidized indophenine (IDTO) isomers, 3 a (E,E,E), 3 b (Z,E,E), and 3 c (Z,E,Z), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most‐stable 3 a by heating at 110 °C. An IDTO‐containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n‐type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm2 V?1 s?1), despite its rather disordered chain packing. 相似文献
104.
Korobko AV Jesse W Lapp A Egelhaaf SU van der Maarel JR 《The Journal of chemical physics》2005,122(2):024902
The structure of spherical micelles of the diblock poly(styrene-block-acrylic acid) [PS-b-PA] copolymer in water was investigated up to concentrations where the polyelectrolyte coronal layers have to shrink and/or interpenetrate in order to accommodate the micelles in the increasingly crowded volume. We obtained the partial structure factors pertaining to the core and corona density correlations with small angle neutron scattering and contrast matching in the water. The counterion structure factor was obtained with small angle x-ray scattering (SAXS) with a synchrotron radiation source. Furthermore, we have measured the flow curves and dynamic visco-elastic moduli. The functionality of the micelles is fixed with a 9 nm diameter PS core and a corona formed by around 100 PA arms. As shown by the SAXS intensities, the counterions are distributed in the coronal layer with the same density profile as the corona forming segments. Irrespective ionic strength and micelle charge, the corona shrinks with increasing packing fraction. At high charge and minimal screening conditions, the polyelectrolyte chains remain almost fully stretched and they interdigitate once the volume fraction exceeds the critical value 0.53+/-0.02. Interpenetration of the polyelectrolyte brushes also controls the fluid rheology: The viscosity increases by three orders of magnitude and the parallel frequency scaling behavior of the dynamic moduli suggests the formation of a physical gel. In excess salt, the coronal layers are less extended and they do not interpenetrate in the present concentration range. 相似文献
105.
Keith A. Brown David Issadore Jesse Berezovsky R.M. Westervelt 《Journal of magnetism and magnetic materials》2010,322(20):3122-2026
The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles decreases the transverse nuclear magnetic resonance (NMR) relaxation time of adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse-echo sequence. This effect is commonly used to measure the concentrations of a variety of small molecules. We perform extensive Monte Carlo simulations of water diffusing around SPIO nanoparticle aggregates to determine the relationship between and details of the aggregate. We find that in the motional averaging regime scales as a power law with the number N of nanoparticles in an aggregate. The specific scaling is dependent on the fractal dimension d of the aggregates. We find for aggregates with d=2.2, a value typical of diffusion limited aggregation. We also find that in two-nanoparticle systems, is strongly dependent on the orientation of the two nanoparticles relative to the external magnetic field, which implies that it may be possible to sense the orientation of a two-nanoparticle aggregate. To optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is best to have aggregates with few nanoparticles, close together, measured with long pulse-echo times. 相似文献
106.
107.
Margaret W. Geiger Margaret M. Elliot Velissarios D. Karacostas Thomas J. Moricone Jesse B. Salmon Vincent L. Sideli Martha A. St . Onge 《Photochemistry and photobiology》1984,40(4):545-548
Abstract A series of ring-substituted phenyl and naphthyl azides have been prepared. Electronic absorption spectral properties and quantum yields of disappearance have been determined in aqueous solution. For phenyl azide derivatives, the wavelengths of maximum absorption vary systematically, correlating with electronic effects of the ring substituents. Quantum yield values of 0.1–0.7 are obtained and are independent of a number of experimental conditions, including concentration. There is no simple correlation of the quantum yields of azide disappearance with electronic effects, except that the naphthyl azides have higher photochemical efficiencies than the phenyl azide derivatives. A series of potential protein photolabels has been identified based on electronic absorption characteristics and photochemical efficiencies. 相似文献
108.
Tricyclic analogs 2a and 8 were prepared by four-step routes. The key step was an intermolecular hetero Diels-Alder reaction involving a quinone methide. 相似文献
109.
The enthalpies of reaction of the complexes (acac)M(olefin)2 (acac=acetyl-acetonate, M=Rh(I), Ir(I); olefin=ethylene, propene, vinyl chloride, vinyl acetate, methyl acrylate and styrene) with 1,5-cyclooctadiene in n-heptane, according to the reaction [(acac)M(olefin)2 + 1,5COD → (acac)M(1,5COD) + 2 olefin]n.heptane have been determined by solution calorimetry. From these results the influence of substituent R in the olefin CH2CHR on the M---(CH2CHR) displacement enthalpy has been derived. It is concluded that π back-bonding is slightly more important in the Ir---olefin bond than in the Rh---olefin bond. Furthermore, the data show that, as a result of steric factors which inhibit the approach of solvent molecules, solvation enthalpies are not additive. 相似文献
110.
On the RbNiCrF6 Type. V. New Fluorides of the Type CsBMF6 with B = MnII or NiII and M = Ga, Fe, Rh or Sc, In, Tl, Rh New prepared are the cubic compounds CsNiScF6 (light yellow, a = 10.60 Å); CsNiInF6 (lightyellow, a = 10.64 Å); CsNiTlF6 (light yellow, a = 10.60 Å); CsNiRhF6 (light redbrown, a = 10.37 Å); CsMnGaF6 (pink, a = 10.42 Å); CsMnFeF6 (light green, a = 10.55 Å) and CsMnRhF6 (redbrown, a = 10.58 Å), all RbNiCrF6 type of structure. The Madelung part of lattice energy, MAPLE, is calculated and discussed. 相似文献