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51.
Hirai A Matsui A Komatsu K Tanino K Miyashita M 《Chemical communications (Cambridge, England)》2002,(17):1970-1971
A highly regio- and stereoselective alpha-methylation reaction of gamma,delta-epoxy-alpha,beta-unsaturated esters was achieved by using a Me2Zn-CuCN reagent. 相似文献
52.
Meso and racemic isomers of 1,1′-bis(α-hydroxyalkyl)ferrocene derivatives, and trans and cis isomers of 7-oxa[3]ferrocenophanes have been isolated. The configurations of these isomers have been determined both by spectroscopy and from their reaction behavior. It has been found that the ring-closure and ring-opening interconversion reactions between 1,1′-bis(α-hydroxyalkyl)ferrocenes and 7-oxa[3]ferrocenophanes are stereospecific. PMR spectra of the diols and ethers have been examined at 100 MHz in CF3COOH, and the existence of α-[1′-(α-hydroxyalkyl)ferrocenyl]carbonium ions has been demonstrated in this acid. A mechanism for the various interconversion reactions is proposed on the basis of their stereospecific reactivity and from the PMR spectra of the carbonium ions. 相似文献
53.
The elemental analysis and morphology of individual particles indicate that the dominant suspended particles in river water are kaolin covered with hydrated iron(III) oxide which strongly sorbs humic substances. Suspended particles, about 1 mg, collected from 250 ml of water by centrifugation, are treated with 0.7 ml of 0.1M sodium hydroxide to desorb humic substances. Approximately 60% of copper and 30% of lead on or in suspended particles exist as humic complexes. 相似文献
54.
Atsushi Mizuike 《中国化学会会志》1990,37(2):117-124
Trace element speciation has recently become one of the most important problems in water analysis. Proper combination of preconcentration techniques with instrumental determination methods is essential to speciation analysis, because sensitivity and selectivity of direct determination methods are generally lacking. The present paper describes such preconcentration techniques as filtration, centrifugation, flotation and sorption, which have been developed in the author's laboratory for the speciation of heavy metals in river and pond waters by electron microscopy, X-ray microanalysis and chemical analysis. The application of freeze concentration to the speciation of silica in high-purity waters is also discussed. 相似文献
55.
Sub-Doppler high-resolution excitation spectra and the Zeeman effects of the 6(0)(1), 1(0)(1)6(0)(1), and 1(0)(2)6(0)(1) bands of the S1(1)B2u<--S(0)(1)A1g transition of benzene were measured by crossing laser beam perpendicular to a collimated molecular beam. 1593 rotational lines of the 1(0) (1)6(0) (1) band and 928 lines of the 1(0)(2)6(0)(1) band were assigned, and the molecular constants of the excited states were determined. Energy shifts were observed for the S1(1)B2u(v1=1,v6=1,J,Kl=-11) levels, and those were identified as originating from a perpendicular Coriolis interaction. Many energy shifts were observed for the S1(1)B2u(v1=2,v6=1,J,Kl) levels. The Zeeman splitting of a given J level was observed to increase with K and reach the maximum at K=J, which demonstrates that the magnetic moment lies perpendicular to the molecular plane. The Zeeman splittings of the K=J levels were observed to increase linearly with J. From the analysis, the magnetic moment is shown to be originating mostly from mixing of the S1(1)B2u and S2(1)B1u states by the J-L coupling (electronic Coriolis interaction). The number of perturbations was observed to increase as the excess energy increases, and all the perturbing levels were found to be a singlet state from the Zeeman spectra. 相似文献
56.
We have performed Monte Carlo simulations of hard spheres under gravity. Vertical boundaries are hard walls, which are well separated with each other. On the other hand, the periodic boundary condition is imposed in the horizontal direction. While we previously reported enhancement of crystallinity as well as crystallization due to gravity, we present here the results that demonstrate the succession of a defect. In case that the crystal formed at the bottom of the system includes kinds of stacking disorders for the (0 0 1) growth, twin band structure develops as mediated by a stacking disorder succeeded in the crystal formed in the fluid region which lies on the bottom crystal. In case that the stacking structure along horizontal direction changes from the (1 1 1) stacking to the (0 0 1) stacking, twin band structure in the (0 0 1) stacking region develops as succeeded in the crystal transformed. The twin band structure also becomes large with its upward growth. 相似文献
57.
Tadatomi Nishikubo Atsushi Kameyama Jun Yamashita Takahiro Fukumitsu Chika Maejima Masao Tomoi 《Journal of polymer science. Part A, Polymer chemistry》1995,33(7):1011-1017
The addition reaction of oxiranes ( 15a-d ) with carbon dioxide (CO2) was carried out using 1 mol % of soluble polymer-supported quaternary onium salts as catalysts under atmospheric pressure. The reaction of 15a-d with CO2 proceeded very smoothly to give the corresponding five-membered cyclic carbonates ( 16a-d ) in high yields at 90-100°C. The catalytic activity of the soluble polymer-supported quaternary onium salts was strongly affected by the following factors: kind of reaction solvent, degree of introduction of the pendant onium salt residues in the polymer chain, and type of alkyl group on the onium salts due to the balance between lipophilicity and steric hindrance of the onium salt residue. Furthermore, these soluble polymer-supported quaternary onium salts were found ordinarily to have higher catalytic activity than low molecular weight quaternary onium salts under the same reaction conditions. It was also found that the rate of reaction was proportional both to catalyst concentration and to oxirane concentration. © 1995 John Wiley & Sons, Inc. 相似文献
58.
Fujitani T Nakamura I Kobayashi Y Takahashi A Haneda M Hamada H 《The journal of physical chemistry. B》2005,109(37):17603-17607
Adsorption and reactions of NO on clean and CO-precovered Ir(111) were investigated by means of X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HR-EELS), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption (TPD). Two NO adsorption states, indicative of fcc-hollow sites and atop sites, were present on the Ir(111) surface at saturation coverage. NO adsorbed on hollow sites dissociated to Na and Oa at temperatures above 283 K. The dissociated Na desorbed to form N2 by recombination of Na at 574 K and by a disproportionation reaction between atop-NO and Na at 471 K. Preadsorbed CO inhibited the adsorption of NO on atop sites, whereas adsorption on hollow sites was not affected by the coexistence of CO. The adsorbed CO reacted with dissociated Oa and desorbed as CO2 at 574 K. 相似文献
59.
Turowski M Yamakawa N Meller J Kimata K Ikegami T Hosoya K Tanaka N Thornton ER 《Journal of the American Chemical Society》2003,125(45):13836-13849
Hydrogen/deuterium isotope effects on hydrophobic binding were examined by means of reversed-phase chromatographic separation of protiated and deuterated isotopologue pairs for a set of 10 nonpolar and low-polarity compounds with 10 stationary phases having alkyl and aryl groups bonded to the silica surface. It was found that protiated compounds bind to nonpolar moieties attached to silica more strongly than deuterated ones, demonstrating that the CH/CD bonds of the solutes are weakened or have less restricted motions when bound in the stationary phase compared with the aqueous solvent (mobile phase). The interactions responsible for binding have been further characterized by studies of the effects of changes in mobile phase composition, temperature dependence of binding, and QSRR (quantitative structure-chromatographic retention relationship) analysis, demonstrating the importance of enthalpic effects in binding and differentiation between the isotopologues. To explain our results showing the active role of the hydrophobic (stationary) phase we propose a plausible model that includes specific contributions from aromatic edge-to-face attractive interactions and attractive interactions of aliphatic groups with the pi clouds of aromatic groups present as the solute or in the stationary phase. 相似文献
60.
Chiral resolution of native DL-tartaric acid was achieved by ion-pair capillary electrophoresis (CE) using an aqueous-ethanol background electrolyte with (1R,2R)-(-)-1,2-diaminocyclohexane (R-DACH) as a chiral counterion. Factors affecting chiral resolution and migration time of tartaric acid were studied. By increasing the viscosity of the background electrolyte and the ion-pair formation, using organic solvents with a lower relative dielectric constant, resulted in a longer migration time. The optimum conditions for both high resolution and short migration time of tartaric acid were found to be a mixture of 65% v/v ethanol and 35% v/v aqueous solution containing 30 mM R-DACH and 75 mM phosphoric acid (pH 5.1) with an applied voltage of -30 kV at 25 degrees C, using direct detection at 200 nm. By using this system, the resolution (Rs) of racemic tartaric acid was approximately 1. The electrophoretic patterns of tartaric and malic acids suggest that two carboxyl groups and two hydroxyl groups of tartaric acid are associated with the enantioseparation of tartaric acid by the proposed CE method. 相似文献