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31.
A novel cyclization of 1,1-diethyl 2-tert-butyl ethenetricarboxylate (1a) in the presence of a Lewis acid afforded a 5,5-dimethyl-gamma-lactone derivative 2a. The reaction process has been shown to arise from formation by trapping of isobutylene generated in situ. Lewis acid-promoted intermolecular reactions of 1,1-diethyl 2-hydrogen ethenetricarboxylate (5) and various alkenes to afford highly functionalized gamma-lactones were also developed. [reaction: see text] 相似文献
32.
Tsuboyama A Takiguchi T Okada S Osawa M Hoshino M Ueno K 《Dalton transactions (Cambridge, England : 2003)》2004,(8):1115-1116
The synthesis, structure, and photophysical properties of a new cyclometalated dinuclear iridium complex, (ppy)2Ir(mu-BPB)Ir(ppy)2 [ppy = 2-phenylpyridine, BPB = 1,4-bis(pyridin-2-yl)benzene], have been investigated. 相似文献
33.
Construction of eight-membered carbocyclic rings via the intramolecular B-alkyl Suzuki-Miyaura cross-coupling reaction has been studied. This protocol proved its potency through the formation of the eight-membered ring possessing a quaternary carbon on its ring in high yield, affording promise of a new access to the eight-membered ring of Taxol. [reaction: see text] 相似文献
34.
Kotaro Nagatani Yunosuke Hoshino Haruka Tezuka Masahisa Nakada 《Tetrahedron letters》2017,58(10):959-962
A synthetic pathway to the C-ring fragment of cotylenin A which emerged from our retrosynthetic analysis of cotylenin A is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of the α-diazo-β-keto ester bearing 2,4,6-trimethylphenyl group as the ester part has been found to afford the crystalline product with high ee, which allowed to establish the approach to the C-ring fragment which required ten-pot operations. The developed approach would be beneficial to a large scale synthesis of the C-ring fragment for the total synthesis of cotylenin A. 相似文献
35.
Oriented films of cellulose prepared from algal cellulose were hydrothermally treated to convert them into highly crystalline cellulose Iβ. The lateral thermal expansion behavior of the prepared cellulose Iβ films was investigated using X-ray diffraction at temperatures from 20 to 300 °C. Cellulose Iβ was transformed into the high-temperature phase when the temperature was above 230 °C, allowing the lateral thermal expansion coefficient of cellulose Iβ and its high-temperature phase to be measured. For cellulose Iβ, the thermal expansion coefficients (TECs) of the a- and b-axes were αa = 9.8 × 10−5 °C−1 and αb = 1.2 × 10−5 °C−1, respectively. This anisotropic thermal expansion behavior in the lateral direction is ascribed to the crystal structure and to the hydrogen-bonding system of cellulose Iβ. For the high-temperature phase, the anisotropy was more conspicuous, and the TECs of the a- and b-axes were αa = 19.8 × 10−5 °C−1 and αb = −1.6 × 10−5 °C−1, respectively. Synchrotron X-ray fiber diffraction diagrams of the high-temperature phase were also recorded at 250 °C. The cellulose high-temperature phase is composed of a two-chain monoclinic unit cell, a = 0.819 nm, b = 0.818 nm, c (fiber repeat) = 1.037 nm, and γ = 96.4°, with space group = P21. The volume of this cell is 4.6% larger than that of cellulose Iβ at 30 °C. 相似文献
36.
The steady-shear viscosity, dynamic viscoelasticity, and sedimentation behavior were measured for silica suspensions dispersed
in aqueous solutions of poly(ethylene oxide) (PEO). For suspensions prepared with polymer solutions in which the transient
network is developed by entanglements, the viscosity at a given shear rate decreases, shows a minimum, and then increases
with increasing particle concentration. Because the suspensions are sterically stabilized under the conditions where the particle
surfaces are fully covered with by a thick layer of adsorbed polymer, the viscosity decrease can be attributed to the reduction
of network density in solution. But under the low coverage conditions, the particles are flocculated by bridging and this
leads to a viscosity increase with shear-thinning profiles. The polymer chains with high molecular weights form flexible bridges
between particles. The stress-dependent curve of storage modulus measured by a stress amplitude sweep shows an increase prior
to a drastic drop due to structural breakdown. The increase in elastic responses may arise from the restoring forces of extended
bridges with high deformability. The effect of PEO on the rheological behavior of silica suspensions can be explained by a
combination of concentration reduction of polymer in solution and flocculation by bridging. 相似文献
37.
Rheology of oil-in-water emulsions 总被引:4,自引:0,他引:4
The effect of interfacial tension on the steady-flow and dynamic viscoelastic behavior of emulsions are studied experimentally. At very low inter-facial tensions and low volume fractions, the viscosity decreases with increasing shear rate and becomes constant at high shear rates. The high-shear-rate Newtonian viscosity is not affected by interfacial tension, but the transition from pseudoplastic to Newtonian flow shifts to lower shear rates as the interfacial tension decreases. At an interfacial tension of 5 × 10–3 Nm–1, the viscosity decreases, passes through a minimum, and then increases as the shear rate is increased. The dilatant behavior may be attributed to elastic responses of interfaces during collision of drops. At high volume fractions, the emulsions show remarkable elasticity resulting from the interfacial energy associated with deformation of liquid films. The modulus and viscosity are proportional to interfacial tension and inversely proportional to drop size. 相似文献
38.
Masahisa Wada Yoshiharu Nishiyama Giovanni Bellesia Trevor Forsyth S. Gnanakaran Paul Langan 《Cellulose (London, England)》2011,18(2):191-206
The hydrogen bond arrangement in a complex of cellulose with ammonia has been studied using neutron crystallography in combination
with molecular dynamics simulations. The O6 atom of the hydroxymethyl group is donor in a highly occupied hydrogen bond to
an ammonia molecule. This rotating ammonia molecule is donor in partially occupied and transient hydrogen bonds to the O2,
O3 and O6 atoms of the hydroxyl groups of other chains. The hydrogen atom bound to the O3 atom is disordered but it is almost
always involved in some type of hydrogen bonding. It is donated in a hydrogen bond most of the time to the O5 atom on the
same chain. However, it also rotates away from this O5 atom to be donated to an ammonia molecule part of the time. On the
other hand the hydrogen atom bound to the O2 atom is free from hydrogen bonding most of the time. It is donated in a hydrogen
bond to the O6 atom on a neighboring chain only with a relatively small probability. These results provide new insights into
how hydrogen bonds are rearranged during the conversion of cellulose I to cellulose IIII by ammonia treatment. 相似文献
39.
Noriyuki Otsubo 《Journal of Number Theory》2011,131(4):648-660
We compare two calculations due to Bloch and the author of the regulator of an elliptic curve with complex multiplication which is a quotient of a Fermat curve, and express the special value of its L-function at s=0 in terms of special values of generalized hypergeometric functions. 相似文献
40.
Kenichi Haji Yong Zhu Masahisa Otsubo Tatsuya Sakoda 《Polymer Degradation and Stability》2008,93(12):2214-2221
The effect of electrolyte conductivity on the partial arc discharge development between two electrolyte electrodes on a silicone rubber sheet surface was investigated. Tests were executed by placing the salt-waterlogged glass-filter paper on a silicone rubber sheet to simulate a polluted electrolyte layer, and partial arc discharges with a constant current value of 10 mA were observed. It was found that the formation of an arc channel and a temperature distribution on the sample surface varied with the electrolyte conductivity. In addition, the relation between the electrolyte conductivity and the weight loss due to the heat erosion of specimens was also investigated by a 3D morphological observation and a simulated calculation. The partial arc discharge did significantly not influence on the sample surface erosion under serious polluted conditions. In contrast, the severest erosion appeared under the light pollution with comparatively lower conductivity of the electrolyte electrodes. 相似文献