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41.
[reaction: see text] D-Mannono-1,4-lactone was efficiently converted into L-ribose in eight steps. A key step of this synthesis is the cyclization of a gamma-hydroxyalkoxamate under Mitsunobu conditions. It is noteworthy that the O-alkylation product was obtained in 94% yield and that none of the N-alkylation product was detected in this cyclization. 相似文献
42.
43.
Toshihiro Iwai 《International Journal of Theoretical Physics》1975,12(6):383-391
Invariance properties of the equations of motion are considered from the differential geometric viewpoint, on making use of vector fields and differential forms. It will be shown that the kinematical symmetries generated from first integrals and the invariance such as the dilation can be treated on an equal footing. 相似文献
44.
Fujikawa Y Nagao T Yamada-Takamura Y Sakurai T Hashimoto T Morikawa Y Terakura K Lagally MG 《Physical review letters》2005,94(8):086105
The structure and stability of the hydrogen-terminated (105) surface of Ge deposited on Si(105) substrates are investigated by scanning tunneling microscopy (STM). Investigations combining STM, electron energy loss spectroscopy, and theory reveal that Si incorporation into the surface Ge layer of hydrogen-terminated Ge/Si(105) drastically destabilizes the surface. The STM images obtained on this surface are well explained by the recently established rebonded-step structure model. 相似文献
45.
The spin-state-dependent reactivity, singlet versus triplet, of the 2-spiroepoxy-1,3-cyclopentane-1,3-diyl DR2 has been assessed through alcohol-trapping reactions for which the effect of solvent acidity on the product distribution of the alcohol trapping products 2 versus 3 + 4 and stereochemical deuterium-labeling studies have been performed. The proposed mechanism for the solvent effect on the product ratio (2/3 + 4) reveals the importance of the hydrogen-bonded intermediates I1 and I2 in the trapping reactions; the stereochemical deuterium-labeling results clarify the dipole structure trapped by the alcohol. The dipoles DP1 and DP2, in which the configuration between the epoxide oxygen and the deuterium atoms is retained, are inferred for the direct photodenitrogenation reactions (singlet state), whereas for the benzophenone-sensitized photoreactions (triplet state), after ISC, the ring-opened dipole DP3 is implied as the intermediate that is trapped by the alcohol. 相似文献
46.
Russulanorol (1), a new norsesquiterpenoid with a novel carbon skeleton, was isolated from the fruiting bodies of Russula delica FR. (Russulaceae) together with three known sesquiterpenoids. The structure of 1 was elucidated on the basis of spectral data and chemical transformation. Compound 1 is an equilibrium mixture of two stereoisomers (1a, b) on the C-11 acetal carbon. 相似文献
47.
Environmentally important aromatic amines are determined by micellar electrokinetic chromatography (MEKC) with UV detection. Using a combination of field-enhanced sample injection in the capillary zone electrophoresis format (performed for a longer period than usual, e.g., 200 s at high voltages; cation selective exhaustive injection) and sweeping in the MEKC format, from 10(4)- to 10(5)-fold improvements in detector response are achieved for all positively chargeable test analytes. Preliminary results indicate that limits of detection for the positively chargeable aromatic amines are in the parts per trillion (ppt) levels. 相似文献
48.
Yoshiaki Tanaka Tatsuo Fujii Yoshihiro Kusano Yasunori Ikeda 《Solid State Communications》2007,141(3):122-126
Single-phases of Pb-substituted Bi-Ca-Co-O misfit-layer cobaltites with various Pb concentrations have been synthesized and the Pb-substitution effects on the structural, electrical and magnetic properties have been systematically investigated. Powder X-ray diffraction analysis showed that the single-phases of Bi1.8−x/2PbxCa2Co2Oz were obtained up to x=0.6-0.7 under the optimized synthesis conditions. The lattice parameters of Bi1.8−x/2PbxCa2Co2Oz continuously changed with increasing Pb concentration. The electron diffraction analysis suggested that the structure consisted of two different sublattices with a rock salt structure (RS) and a hexagonal CdI2 structure (H), respectively, without modulation. In combined with the chemical composition analysis, the chemical formulas of the x=0 and x=0.6 samples were determined approximately as [Bi1.74Co0.31Ca2.01O4]RS[CoO2]1.69 and [Bi1.47Pb0.38Co0.29Ca1.98O4]RS[CoO2]1.71, respectively. The electrical resistivity became more metallic with increasing the Pb concentration up to x=0.6. Moreover, the Pb-substitution simultaneously increased the antiferromagnetic Weiss temperatures and decreased the effective magnetic moments of the Co ions. 相似文献
49.
50.
We study relations between induced subgraphs and (n,m)-subposets. Using properties of (n,m)-subposets, we consider a characterization of chordal double bound graphs in terms of forbidden subposets. Furthermore, we deal with properties of a poset whose double bound graph is isomorphic to its upper bound graph or its comparability graph, etc. 相似文献