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41.
Aqueous permanganate oxidation of 8(17)-labden-13-ol gave two novel oxidation products by functionalisation of an unactivated carbon atom. The structures have been confirmed by degradative studies and a mechanism to account for their formation is proposed. 相似文献
42.
We have conducted a high-level quantum chemistry study of the interactions of 1,2-dimethoxyethane (DME) with water for complexes representing both hydrophilic and hydrophobic hydration. It was found that our previous quantum chemistry-based force field for poly(ethylene oxide) (PEO) and its oligomers in aqueous solution did a poor job in describing the hydrophobic binding of water to the ether, consistent with our recent calculations of the excess free energy and entropy of hydration of DME. Our original force field was revised to more accurately reproduce the interaction of water with the carboneous portions of DME. Molecular dynamics simulations of aqueous DME solutions using the revised quantum chemistry-based potential yielded good agreement with experiment for excess free energy, enthalpy, and volume as well as excess solution viscosity and the self-diffusion of water. Comparison with our original potential revealed that the relatively hydrophobic ether-water interactions in the new potential strongly reduced the favorable excess free energy and enthalpy but have relatively little influence on the excess entropy for dilute DME solutions. Other properties of DME and PEO solutions including conformational populations and dynamics, solution viscosity, hydrogen bonding, water translational and rotational diffusion and neutron structure factor as a function of solution composition were found to be largely unchanged from those obtained using the original potential. 相似文献
43.
Hancock G Horrocks SJ Pearson PJ Ritchie GA Tibbetts DF 《The Journal of chemical physics》2005,122(24):244321
The translational anisotropy and angular momentum polarization of the O(2)(a (1)Delta(g),v = 0;J = 15-27) molecular photofragment produced from the UV photodissociation of O(3) in the range from 270 to 300 nm have been determined using resonance-enhanced multiphoton ionization in conjunction with time-of-flight mass spectrometry. At the shortest photolysis wavelengths used, the fragments exhibit the anisotropic vector correlations expected from a prompt dissociation via the (1)B(2) <--(1)A(1) transition. Deviations from this behavior are observed at longer photolysis wavelengths with, in particular, the angular momentum orientation showing a significant reduction in magnitude. This indicates that the dissociation can no longer be described by a purely impulsive model and a change in geometry of the dissociating molecule is implied. This observation is substantiated by the variation of the translational anisotropy with photolysis wavelength. We also observe that the bipolar moments describing the angular momentum polarization of the odd J states probed are consistently lower in magnitude than those of the even J states and that this variation is observed for all photolysis wavelengths. 相似文献
44.
Grant T. D. Shouldice Phillip Y. Choi Bryan E. Koene Linda F. Nazar Alfred Rudin 《Journal of polymer science. Part A, Polymer chemistry》1995,33(9):1409-1417
The dominant species in the early stages of an emulsifier-free emulsion polymerization of styrene has been found to be an oligomer of two to three monomer units using a novel trapping technique. This involved the intercalation of charged primary oligomers between the layers of a hydrotalcite, [Mg4Al2(OH)12]2+[A]2- (where A = dianion). Hydrotalcites are an important class of lamellar, inorganic compounds whose interlayer spacing can be mod-ified by anion exchange. Our approach first involved preparing a hydrotalcite precursor in which the layers were propped apart by an organic dianion (terephthalate = TA). This material was then used to capture the negatively charged polystyrene oligomers from the emulsion polymerization reaction mixture. We found that TA was rapidly ion-exchanged for the charged oligomers. The resulting pillared hydrotalcite material was characterized using XRD and SEC. We found that the interlayer spacing between the hydroxide layers increased to 23.2 Å on exposure to the emulsion reaction mixture. This represents an interlayer expansion of 18.3 Å (after subtraction of the hydroxide layer contribution), which is cnsistent with intercalation of oligomers with two to three monomer units arranged in a bilayer. This size estimate was confirmed by the results of size exclusion chromatography. © 1995 John Wiley & Sons, Inc. 相似文献
45.
Grant J. Sherborne Avetik G. Gevondian Ignacio Funes-Ardoiz Amit Dahiya Christoph Fricke Prof. Dr. Franziska Schoenebeck 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(36):15673-15678
Selective C –C couplings are powerful strategies for the rapid and programmable construction of bi- or multiaryls. To this end, the next frontier of synthetic modularity will likely arise from harnessing the coupling space that is orthogonal to the powerful Pd-catalyzed coupling regime. This report details the realization of this concept and presents the fully selective arylation of aryl germanes (which are inert under Pd0/PdII catalysis) in the presence of the valuable functionalities C−BPin, C−SiMe3, C−I, C−Br, C−Cl, which in turn offer versatile opportunities for diversification. The protocol makes use of visible light activation combined with gold catalysis, which facilitates the selective coupling of C−Ge with aryl diazonium salts. Contrary to previous light-/gold-catalyzed couplings of Ar–N2+, which were specialized in Ar–N2+ scope, we present conditions to efficiently couple electron-rich, electron-poor, heterocyclic and sterically hindered aryl diazonium salts. Our computational data suggest that while electron-poor Ar–N2+ salts are readily activated by gold under blue-light irradiation, there is a competing dissociative deactivation pathway for excited electron-rich Ar–N2+, which requires an alternative photo-redox approach to enable productive couplings. 相似文献
46.
Stereoselective syntheses of novel 5,6-difunctionalized-2-azabicyclo[2.1.1]hexanes containing 5-anti-fluoro or hydroxyl in one methano bridge and a variety of syn- or anti-chloro, fluoro, hydroxy, methyl, or phenyl substituents in the other methano bridge have been effected. Rearrangements of iodides to alcohols were initiated using Selectfluor. Rearrangement of alcohols to fluorides was initiated using Deoxo-Fluor. Ring opening of 2-azabicyclo[2.2.0]hex-5-ene exo-epoxide with organocopper reagents is regioselective at C(5). 相似文献
47.
Quartz crystal microbalance (QCM) in high-pressure carbon dioxide (CO2): experimental aspects of QCM theory and CO2 adsorption 总被引:3,自引:0,他引:3
Wu YT Akoto-Ampaw PJ Elbaccouch M Hurrey ML Wallen SL Grant CS 《Langmuir : the ACS journal of surfaces and colloids》2004,20(9):3665-3673
The quartz crystal microbalance (QCM) technique has been developed into a powerful tool for the study of solid-fluid interfaces. This study focuses on the applications of QCM in high-pressure carbon dioxide (CO2) systems. Frequency responses of six QCM crystals with different electrode materials (silver or gold) and roughness values were determined in helium, nitrogen, and carbon dioxide at 35-40 degrees C and at elevated pressures up to 3200 psi. The goal is to experimentally examine the applicability of the traditional QCM theory in high-pressure systems and determine the adsorption of CO2 on the metal surfaces. A new QCM calculation approach was formulated to consider the surface roughness contribution to the frequency shift. It was found that the frequency-roughness correlation factor, Cr, in the new model was critical to the accurate calculation of mass changes on the crystal surface. Experiments and calculations demonstrated that the adsorption (or condensation) of gaseous and supercritical CO2 onto the silver and gold surfaces was as high as 3.6 microg cm(-2) at 40 degrees C when the CO2 densities are lower than 0.85 g cm(-3). The utilization of QCM crystals with different roughness in determining the adsorption of CO2 is also discussed. 相似文献
48.
Kabin JA Withers ST Grant CS Carbonell RG Sáez AE 《Journal of colloid and interface science》2000,228(2):344-358
Measurements have been made of the rate of removal of a solid organic film (phenanthrene) from the surface of a rotating disk using emulsions containing water, the nonionic surfactant Tween 20, and d-limonene as the organic phase. The results show that phenanthrene removal initially occurs by the uptake of phenanthrene into the emulsion drops as small aggregates. Simultaneously, the organic phase penetrates into the phenanthrene film, diminishing the adhesive force between the film and the substrate. After sufficient time, the phenanthrene film detaches from the rotating disk surface as a solid. This detachment mechanism accounts for the vast majority of the phenanthrene removal ( approximately 90%). Initial solubilization rates were analyzed using two solubilization models. Both models assume that phenanthrene removal occurs via a mass transfer limited removal of phenanthrene-laden emulsion drops from the phenanthrene film surface into the bulk solution. One model treats the emulsion as homogeneous while the other accounts for the finite size of the emulsion droplets. The latter model was also used to relate the flux of organic phase impacting the phenanthrene film to the detachment times. Copyright 2000 Academic Press. 相似文献
49.
Jerald S. Bradshaw Patricia K. Thompson Reed M. Izatt Frederick G. Morin David M. Grant 《Journal of heterocyclic chemistry》1984,21(3):897-901
A series of chiral diphenyl-substituted macrocyclic polyether-diester ligands have been prepared from the chiral diphenyl-substituted tetraethylene glycol. Enantiomeric recogntion by the chiral diphenyl-substituted pyridino-diester-18-crown-6 compound ( 7 ) was studied by temperature dependent 1H NMR spectroscopy in deuteriodichloromethane. This ligand exhibited chiral recognition when complexed with the hydrogen per-chlorate salts of (R)- and (S)-α-(1-naphthyl)ethylamine and (R)- and (S)-methyl phenylalaninate. 相似文献
50.