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排序方式: 共有568条查询结果,搜索用时 250 毫秒
561.
Reactions of thioamide dianions, derived from secondary N-arylmethyl thioamides using BuLi, with thioformamides followed by the addition of iodine to yield 5-amino-2-thiazolines are described. Treatment of the 5-amino-2-thiazolines with iodine leads to a highly efficient production of 5-aminothiazoles. When N,N-diarylthioformamides are employed in this process, fluorescent 5-N,N-diarylthiazoles are obtained. 相似文献
562.
A simple, practical, and convenient fluorination of 1,3-dicarbonyl compounds was achieved by direct use of aqueous hydrofluoric acid and iodosylbenzene (PhIO). The reaction of ethyl benzoylacetate with the reagent system of aqueous HF and PhIO in CH(2)Cl(2) gave ethyl 2-fluoro-2-benzolyacetate in 98% yield. Other 1,3-dicarbonyl compounds including β-keto esters and 1,3-diketones underwent the fluorination reaction to give the corresponding fluorinated products in good yields. 相似文献
563.
Sumimoto M Yokogawa D Komeda M Yamamoto H Hori K Fujimoto H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,81(1):653-660
The molecular geometries, electronic structures, and excitation energies of NPh(3), NPh(2)Me, NPhMe(2), and NMe(3), were investigated using DFT and post-Hartree Fock methods. When the structural stabilities of these compounds were compared to results obtained by using MP4(SDQ) method, it was confirmed that the optimized geometries by using MP2 method were sufficiently reliable. The excited states with large oscillator strengths consisted of transition components from the HOMO. It should be noted that the orbitals of the nitrogen atom mix with the π-orbital of the phenyl group in an anti-bonding way in the HOMO, and the orbital energy increases with this mixing. The unoccupied orbitals are generated from bonding and anti-bonding type interactions between the π-orbitals of the phenyl groups; therefore, the number of phenyl groups strongly affects the energy diagram of the compounds studied. The differences in the energy diagram cause a spectral change in these compounds in the ultraviolet region. 相似文献
564.
565.
Crystal structures determined for eight compounds R-C6H4-C6H4-COO-C6H4-R ', where R and R ' are achiral, four with octyloxy and/or octyl chains and four with a methyl or methoxy group at one end, are classified into three modes. First is a smectic-like layer composed of parallel molecules with closely arranged ester linkages; second is a layer comprising two crystallographically independent molecules, among which the ester linkages are close. Compounds with an octyloxy chain take these modes. Thirdly, for molecules with alkyl chains, the ester linkages are far apart among the parallel molecules. Melting and clearing points suggest stronger intermolecular interactions in the former two modes than in the last mode. 相似文献
566.
Hiroshi Ohrui Yoshihiro Nishida Hiroshi Hori Hiroshi Meguro Shoji Zushi 《Journal of carbohydrate chemistry》2013,32(4):711-731
Abstract 1-O-Methyl analogs of mucin oligosaccharide components, D-GalNAc (1a and 1b). β-D-Galp-(1-3)-D-GalNAc (2) and β-D-Galp(1-3)-[β-D-GlcNAc-(1-6)]-D-GalNAc (3) in which the H-6proS proton was selectively replaced by a deuterium, were synthesized to study the solution conformations about the C5-C6 fragments by 1H-NMR spectroscopy. The study revealed the preference of the gt-conformer for these sugars. 相似文献
567.
Farah Fahma Shinichiro Iwamoto Naruhito Hori Tadahisa Iwata Akio Takemura 《Cellulose (London, England)》2011,18(2):443-450
Three different pre-acid-hydrolysis treatments were used to treat coconut husk fibers for preparing cellulose nanowhiskers
by sulfuric acid hydrolysis. The effects of those treatments on the morphology and properties of the nanowhiskers were investigated.
FTIR was employed to evaluate the change of chemical composition due to different pre-acid-hydrolysis treatments. AFM images
showed that there was no significant difference of size of nanowhiskers obtained by different pre-acid-hydrolysis treatment,
2–3 nm of average thickness. The thermal decomposition of nanowhiskers shifted to higher temperatures with removal of hemicellulose
and lignin. 相似文献
568.
Hori Y Kato K 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2008,84(8):287-320
In high speed rotating machines such as turbines and generators, vibrations of a rotating shaft often hinder the smooth operation of the machine or even cause failure. Oil whip is one of such vibrations due to oil film action of journal bearing. Its mechanism and preventive method is explained and proposed in this paper. Further theoretical and experimental analyses are made for considering heat generation and temperature rise in hydrodynamic lubrication. The usefulness of the lubrication theory based on the k-epsilon model is also shown for bearings with high eccentricity ratios. In the latter half of this paper, water lubrication, nitrogen gas lubrication and tribo-coated indium lubrication are shown as new promising methods, and their mechanisms are discussed and the importance of tribo-layer is explained. Some mechanisms of wear are introduced for better understanding of tribo-layer. In the last part of this paper, the mechanisms of generating static friction are shown for the cases of plastic contact and elastic contact, which is the base for understanding the mechanism of initiation of macroscopic sliding. 相似文献