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51.
Diiodo- and bromo, iodo-substituted dibenzopentalenes were obtained by treatment of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene with I(2) and IBr, respectively. These dihalo-substituted pentalenes reacted with terminal ethynes in Sonogashira coupling and with arylboronic acid in Suzuki-Miyaura coupling to give a series of phenylethynyl- and/or aryl-substituted pentalenes. Suzuki-Miyaura coupling of the halopentalenes with in situ prepared pentaleneboronic esters provided bis-, tri-, and tetra(dibenzopentalene)s. It was found that these dibenzopentalene oligomers underwent facile electrochemical reduction and exhibited a bathochromic shift in UV-vis absorption spectra because of their expanded π-systems. 相似文献
52.
There have been extensive studies on the large time behavior of solutions to systems on gas motions, such as the Navier-Stokes
equations and the Boltzmann equation. Recently, an approach is introduced by combining the energy method and the spectral
analysis to the study of the optimal rates of convergence to the asymptotic profiles. In this paper, we will first illustrate
this method by using some simple model and then we will present some recent results on the Navier-Stokes equations and the
Boltzmann equation. Precisely, we prove the stability of the non-trivial steady state for the Navier-Stokes equations with
potential forces and also obtain the optimal rate of convergence of solutions toward the steady state. The same issue was
also studied for the Boltzmann equation in the presence of the general time-space dependent forces. It is expected that this
approach can also be applied to other dissipative systems in fluid dynamics and kinetic models such as the model system of
radiating gas and the Vlasov-Poisson-Boltzmann system.
相似文献
53.
Radjesvarane Alexandre Yoshinori Morimoto Seiji Ukai Chao-Jiang Xu Tong Yang 《Archive for Rational Mechanics and Analysis》2010,198(1):39-123
The Boltzmann equation without Grad’s angular cutoff assumption is believed to have a regularizing effect on the solutions
because of the non-integrable angular singularity of the cross-section. However, even though this has been justified satisfactorily
for the spatially homogeneous Boltzmann equation, it is still basically unsolved for the spatially inhomogeneous Boltzmann
equation. In this paper, by sharpening the coercivity and upper bound estimates for the collision operator, establishing the
hypo-ellipticity of the Boltzmann operator based on a generalized version of the uncertainty principle, and analyzing the
commutators between the collision operator and some weighted pseudo-differential operators, we prove the regularizing effect
in all (time, space and velocity) variables on the solutions when some mild regularity is imposed on these solutions. For
completeness, we also show that when the initial data has this mild regularity and a Maxwellian type decay in the velocity
variable, there exists a unique local solution with the same regularity, so that this solution acquires the C
∞ regularity for any positive time. 相似文献
54.
55.
Stereoselective reduction of α-substituted β-keto esters is achieved by the combined use of hydrostannane/organotin triflate. syn-Aldols are obtained with more than 90% selectivities. 相似文献
56.
Elliott EL Orita A Hasegawa D Gantzel P Otera J Siegel JS 《Organic & biomolecular chemistry》2005,3(4):581-583
The X-ray crystal structure and photophysical properties of 1,6,7,12,13,18,19,24-octamethylacenaphthyleno[b,l]tetraphenylene, which has been synthesized via a Diels-Alder reaction of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene and 6,7-dihydro-6-hydroxy-7,9-dimethyl-8H-cyclopenta[a]acenaphthylene-8-one, are reported. 相似文献
57.
58.
Uota M Arakawa H Kitamura N Yoshimura T Tanaka J Kijima T 《Langmuir : the ACS journal of surfaces and colloids》2005,21(10):4724-4728
A new surfactant-mediated approach was developed to synthesize hydroxyapatite (HAp) nanoparticles with high surface areas by calcination of their precursors encapsulated with calcium stearate using mixed surfactant-containing reaction mixtures. Acidic aqueous solution of calcium phosphate was mixed with both or either nonaoxyethylene dodecyl ether (C12EO9) and polyoxyethylene(20) sorbitan monostearate (Tween 60) and then was treated with aqueous ammonium at 25 degrees C. The C12EO9-based single surfactant system yielded an aggregate of platy HAp nanoparticles 20-40 nm in size, whereas the Tween 60-based single and mixed systems led to lath-shaped HAp nanoparticles 2-8 nm wide and encapsulated with calcium stearate. On calcination at 500 degrees C, the stearate-encapsulated HAp nanoparticles in the latter two systems were deorganized into high surface area HAp nanoparticles. Particularly, the HAp nanoparticles in the mixed system exhibited a specific surface area as high as 364 m2 g(-1) that is roughly 3 times larger than 160 m2 g(-1) for those in the single system. The significantly high surface area for the former is attributed to much less adhesion of decapsulated HAp nanoparticles, which originated from the particle-separating effect of the C12EO9 molecules adsorbed on the outer surface of the stearate-encapsulated HAp nanoparticles to inhibit their agglomeration or interfacial coordination. The present results demonstrate that the mixed use of two different surfactants as a source of encapsulating and templating agent and a particle-separating agent is specifically effective for the synthesis of high surface area HAp nanoparticles. 相似文献
59.
60.
Orita A An DL Nakano T Yaruva J Ma N Otera J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(9):2005-2010
A new strategy for constructing enantiopure acetylenic cyclophanes is described on the basis of one-pot double elimination reaction starting from dialdehydes and bis(sulfoximine)s. In this case, the conventional sulfone protocol affords poorer yields of the desired cyclophanes. Thus, arylene-ethynylene moieties with terminal sulfoximine or formyl functions are linked to binaphthyl cores and these building blocks are then subjected to double elimination reaction. The desired macrocycles are obtained in up to 35 % yield. The corresponding Sonogashira coupling fails to afford cyclophanes indicative of effectiveness of the double elimination methodology. 相似文献