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41.
Kurono N Ohtsuga K Wakabayashi M Kondo T Ooka H Ohkuma T 《The Journal of organic chemistry》2011,76(24):10312-10318
Kinetic resolution of sterically hindered racemic α-tert-alkyl-α-hydroxy esters is performed by enantiomer-selective carbamoylation with the t-Bu-Box-Cu(II) catalyst (Box = bis(oxazoline)). The reaction with 0.5 equiv of n-C(3)H(7)NCO is carried out with a substrate-to-catalyst molar ratio of 500-5000 at -20 to 25 °C. The high enantiomer-discrimination ability of the catalyst achieves an excellent stereoselectivity factor (s = k(fast)/k(slow)) of 261 in the best case. A catalytic cycle for this reaction is proposed. 相似文献
42.
Measurements of rate constants and substituent effects for three important elementary steps of proton-transfer reactions of phenylnitromethane were reported. The Hammett ρ values for the deprotonation of ArCH(2)NO(2) with OH(-), protonation of ArCH═NO(2)(-) with H(2)O, and protonation of ArCH═NO(2)(-) with HCl were determined in aqueous MeOH at 25 °C. Comparison of these experimentally observed ρ values with those calculated at B3LYP/6-31G* revealed that aci-nitro species (ArCH═NO(2)H), which is formed on the O-protonation of ArCH═NO(2)(-), does not lie on the main route of the proton-transfer reaction. Analysis of the Br?nsted plot implies that the proton-transfer reaction of most XC(6)H(4)CH(2)NO(2) exhibits nitroalkane anomaly, but not for p-NO(2)C(6)H(4)CH(2)NO(2), and that the transition state charge imbalance is an origin of anomaly. 相似文献
43.
Dr. Yoshihiro Sohtome Bongki Shin Natsuko Horitsugi Prof. Dr. Keiichi Noguchi Prof. Dr. Kazuo Nagasawa 《化学:亚洲杂志》2011,6(9):2463-2470
Herein, we present details of our conformationally flexible, 1,3‐diamine‐tethered guanidine/bisthiourea organocatalysts for chemo‐, regio‐, and enantioselective 1,4‐type Friedel–Crafts reactions of phenols. These organocatalysts show a unique stereo‐discrimination governed by the differential activation entropy (ΔΔS≠), rather than by the differential activation enthalpy (ΔΔH≠). Extensive kinetic analyses using Eyring plots for a series of guanidine/bisthiourea organocatalysts revealed the key structural motif in the catalysts associated with a large magnitude of differential activation entropy (ΔΔS≠). A plausible guanidine–thiourea cooperative mechanism for the enantioselective Friedel–Crafts reaction is proposed. 相似文献
44.
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46.
M. Fujita T. Endo A. Yamazaki T. Sonada T. Miyake E. Tanaka T. Shinozuka T. Suzuki A. Goto Y. Miyashita N. Sato Y. Wakabayashi N. Hokoiwa M. Kibe Y. Gono T. Fukuchi A. Odahara 《Hyperfine Interactions》2004,159(1-4):245-249
The g-factor of the 27− isomer state of 152Dy has been measured using the Time-Integral Perturbed Angular Distribution (TIPAD) method. The high-spin states of 152Dy have been populated by 141Pr(16O,p4n)152Dy reaction at E = 115 MeV from the AVF cyclotron at CYRIC. The paramagnetic correction factor of Dy ions in Pr has been determined to be
4.2(5) by the Time-Differential Perturbed Angular Distribution (TDPAD) measurement of the 21− state of 152Dy. As a result, the g-factor of the 27− isomer state of 152Dy has been obtained to be +0.09(5). This shows the smaller value than the expected one of +0.39 deduced from a fully aligned
configuration of π(h
11/2
2) ⊗ ν(f
7/2
2
h
9/2
i
13/2). 相似文献
47.
A laser Doppler imaging system with a TV camera has been constructed and velocity distributions of fluid flow in cross sections of a rectangular channel have been measured. Consequently, it has been found that the system has some advantages in comparison with usual laser Doppler velocimeters, for example, the visualization of flow can be easily achieved. 相似文献
48.
49.
N. Kunitomi Y. Tsunoda N. Wakabayashi R.M. Nicklow H.G. Smith 《Solid State Communications》1978,25(11):921-924
The phonon dispersion relations of disordered alloys Ni1-xPtx were measured for five specimens covering the full range of atomic concentration by means of neutron inelastic scattering. At the resonant frequencies well separated double peak structures were observed in the phonon spectra. For the specimens with , the energy splitting of the phonon dispersion curve for the L-branch takes place at a higher frequency than that for the T-branch. The maximum phonon energy decreases with increasing Pt concentration but deviates from the theoretical prediction based on the mass defect CPA model. For x = 0.95 the localized mode cannot be observed as a well defined peak and does not seem to be split off from the main phonon band. 相似文献
50.