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排序方式: 共有870条查询结果,搜索用时 15 毫秒
861.
Keiko Kanamori John D. Roberts Mitchell A. Rossman Nelson J. Leonard 《Heteroatom Chemistry》1992,3(1):19-23
Nitrogen-15 NMR spectra were obtained for a systematic series of azacycl[3.3.3]azines: 1,3,4,6,7,9-hexaaza-,1,3,4,6,7-pentaaza-,1,3,4,6-tetraaza-, 1,3,4,6,8-pentaaza-, and 1,3,6-triazacycl[3.3.3]azine. The magnetic resonance data were compared with other physical and spectroscopic properties available for the series relative to the diminishing number of peripheral nitrogens in alternating positions. The properties of 1,3,4,6,8-pentaazacycl[3.3.3]azine, which has a peripheral 1,4-diazine-type nitrogen, are distinct from those of the rest of the series. 相似文献
862.
The citric acid oxidation by vanadium(V) in sulfuric acid medium at 303 K is reported. The reaction rate was determined spectrophotometrically by monitoring the formation of vanadium(IV) at 760 nm. The oxidation showed a first‐order dependence with respect to vanadium(V) concentration and fractional order with respect to citric acid concentrations, with no control and with constant ionic strength. The reaction is also first order with respect to sulfuric acid concentration with no control and of fractional order at constant ionic strength. The reaction rate is enhanced by an increase of ionic strength and increased by a decrease of the dielectric constant. The activation parameters were calculated based on the rate constants determined in the 293 to 313 K interval. The proposed oxidation mechanisms and the derived rate laws are consistent with the experimental rate laws. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 566–572, 2000 相似文献
863.
Carboxymethyl derivatives of amines containing a chiral α-carbon were separated into enantiomers by high-performance liquid chromatography using octadecylsilanized silica gel coated with N-n-dodecyl-L-hydroxyproline as the stationary phase and an aqueous solution containing copper(II) as the mobile phase. Detection was by post-column reaction involving derivatization to tertiary amine and chemiluminescence reaction of ruthenium bipyridine complex. 相似文献
864.
865.
Susumu Saito Keiko Hatanaka Taichi Kano Hisashi Yamamoto 《Angewandte Chemie (International ed. in English)》1998,37(24):3378-3381
A C 2 -symmetrical phenol was used as a chiral auxiliary in the asymmetric aldol reaction of chiral acetates with various aldehydes [Eq. (a)]. The reaction proceeds readily under mild conditions to provide aldol adducts with high enantioselectivity. LDA=lithium diisopropylamide. 相似文献
866.
Shau Mien Ng Shin-ichi Ogino Takuzo Aida Keiko A. Koyano Takashi Tatsumi 《Macromolecular rapid communications》1997,18(12):991-996
Free radical polymerization of methyl methacrylate (MMA) within the uniform channels of the mesoporous zeolite MCM-41 proceeds at 100°C to give a high molecular weight polymer (PMMA). The formation of long-living propagating polymer-radicals is observed by electron paramagnetic resonance (EPR). The molecular weight of PMMA within the mesopores can be controlled over a wide range by changing the monomer-to-initiator mole ratio. 相似文献
867.
Polarized-light induced anisotropy of Disperse Orange 3 (DO3) depending on the polymer matrices was investigated by polarized FTIR spectroscopy. The dynamic behavior of the azo dyes doped in a series of methacrylate polymers was analyzed in terms of the orientation factors. Two factors, the free volume and the local polarity of matrices, are found to govern the dynamic behavior of DO3. It was found that induced anisotropy for trans and cis isomers varies depending on Tg of polymer matrix. Further, the thermal isomerization rate depend on the isomerization mode which is governed by the matrix polarity. The branched-alkyl chains are considered to block the interaction between ester groups and DO3 and introduce the DO3 molecules into the less polar environment. 相似文献
868.
869.
Hiroaki Katayama Hiroyuki Shiraishi Takahiro Hino Takuya Ogane Akio Imai 《Macromolecular Symposia》1995,97(1):109-118
Two types of copolymerizations were found with the catalyst system Cp2ZrCl2/MAO. One was a less exothermic reaction, and another was a more exothermic one. The former provided a polymer with a single composition distribution because of a single cationic active site. The latter provided a polymer with a bimodal composition distribution, indicating the existence of two active sites. The two active sites were investigated through the comparison of MAO systems and alkylaluminium / borate systems. We speculated that the two active sites were the normal cationic site and the active site where the interaction between a cationic metallocene and an aluminium compound was strong. 相似文献
870.