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91.
Akira Ando 《Journal of fluorine chemistry》2005,126(5):765-770
Treatment of 2-chloro-3,3-difluoroprop-2-en-1-ol derivatives (2) with methanesulfonyl chloride in the presence of a base did not give the expected esters but 2-chloro-1,1-difluoroprop-2-enyl methanesulfonates (4) through a novel [3,3] sigmatropic rearrangement. Reaction of 4 with diethylzinc in the presence of tetrakis(triphenylphosphine) palladium gave 1-alkyl- or 1-aryl-2-chloro-3-fluoropenta-1,3-dienes in moderate to good yields through a CC bond formation followed by dehydrofluorination. 相似文献
92.
Yasuko Ishizuka Yoshinobu Nagawa Hiroshi Nakanishi Akira Kuboyama 《Journal of inclusion phenomena and macrocyclic chemistry》1990,9(3):219-225
Two aromatic rings of a phlorizin molecule form inclusion complexes with -CD and -CD. Induced circular dichroism spectra of these complexes have been measured to estimate the orientation of the two aromatic rings in the hydrophobic space of CDs. Apparent complex formation constants have been also estimated for each complex. It is concluded that phlorizin forms a stronger inclusion complex with -CD than with -CD. 相似文献
93.
Kawai K Yoshida H Sugimoto A Fujitsuka M Majima T 《Journal of the American Chemical Society》2005,127(38):13232-13237
The formation of the pyrene (Py) dimer radical cation (Py(2)(*+)) was used to measure the kinetics of the intrastrand end-to-end contact rates of single-stranded DNAs (ssDNAs) in the 10 nanoseconds to the tens of microseconds time range. ssDNAs labeled with Py at both ends with the lengths of 3, 6, and 9 mer were synthesized, and the two-photon ionization method was employed to generate a Py(*+), which enables the measurements of the end-to-end contact rates from 10 ns. The formation rate of Py(2)(*+) depended on the length and the sequence of the ssDNAs, and about 1 order of magnitude faster rates were observed for the T-rich ssDNAs compared to those for the corresponding length of A-rich ssDNAs, showing that ssDNA made from adenines is much more rigid than that composed of thymidines. As for the T-rich ssDNAs, the formation of Py(2)(*+) attributed to the misfolded structures was also observed, which is consistent with the configurational diffusion model suggested by Ansari and co-workers. 相似文献
94.
Silylcarbenes are generated by the pyrolysis of 1,1-bis(trimethylsilyl)-1-alkanols with elimination of trimethylsilanol. 相似文献
95.
Akira Matsumoto Ikuo Tamura Masataka Yamawaki Masayoshi Oiwa 《Journal of polymer science. Part A, Polymer chemistry》1979,17(5):1419-1429
The polymerization of diallyl oxalate was conducted in the presence of radical initiators at a high temperature range of 80–180°C; a large decrease in degree of polymerization, an increase in residual unsaturation of the resulting polymer, and the evolution of carbon dioxide were observed with the elevation of temperature. These findings were reasonably interpreted by considering the dismutation of the uncyclized growing radical to yield the allyl radical, carbon dioxide, and polymer carrying a terminal double bond. The kinetics of the polymerization of diallyl oxalate in the evolution of carbon dioxide at elevated temperatures were also discussed in detail. 相似文献
96.
Summary The “chemical” relaxation of stress either in Amilan (6-Nylon) or polyvinyl alcohol caused by penetration of water vapor was
studied at 40% R. H. and temperatures 15, 30, and 50° C. A theory was presented of the chemical relaxation in a polymer which
comprises penetrant-sensitive bonds as the crosslinkages between the molecular chains. This theory assumes the diffusion coefficient
of penetrant in the polymer to he independent of concentration and any other factors. It was found that the system Amilan-water
behaves in exact conformity with the theory over the ranges of elongation and temperature studied. The diffusion coefficient,D, of water in Amilan could thus be evaluated from the chemical relaxation data, using the theory presented, as functions of
elongation and temperature. An ordinary sorption experiment was carried out for this system at 40% R. H. and 16.8° C and demonstrated
that the diffusion of water in Amilan was Fickian with a constant diffusion coefficient. Both diffusion coefficients from
the chemical relaxation data and the sorption. data were found to agree quite well when the former was extrapolated to zero-strain.
The chemical relaxation behavior in the system polyvinyl alcohol-water was markedly different from that expected from the
theory, suggesting primarily that the diffusion coefficient of water in this polymer was not constant. A parallel evidence
for this fact was obtained from sorption measurements on this system, which demonstrated the diffusion in this system to be
dependent both on concentration and time.
From these results it may be concluded that the chemical relaxation technique, when combined properly with an adequate theory,
can be used not only to evaluate the diffusion coefficient of penetrant in a given polymer solid but also to investigate,
at least qualitatively, the type of sorption behavior characteristic of the system under given experimental conditions.
Zusammenfassung Die chemische Spannungsrelaxation in Amilan (6-Nylon) und Polyvinylalkohol, verursacht durch Eindringen von Wasserdampf, wurde bei 40% r. F. und Temperaturen von 15, 30 und 50° C untersucht. Es wird eine Theorie der chemischen Relaxation von Polymeren vorgelegt, die als empfindliche Bindungen auf das eindringende Niedermolekulare die Vernetzungen zwischen den molekularen Ketten betrachtet. Diese Theorie setzt voraus, da? der Diffusionskoeffizient im Polymeren für die eindringende Substanz unabh?ngig von Konzentration und anderen Faktoren ist. Das System Amilan-Wasser benimmt sich vollkommen entsprechend dieser Theorie in den studierten Verstreckungs- und Temperaturbereiche. Der Diffusionskoeffizient von Wasser in Amilan konnte daher aus der chemischen Relaxation als Funktion von Dehnung und Temperatur ausgewertet werden. Ein normales Quellungsexperiment wurde für das System bei 40% r. F. und 16,8° C ausgeführt und zeigte, da? die Diffusion von Wasser in Amilan dem Fickschen Gesetz mit konstantem Diffusionskoeffizienten folgt. Beide Diffusionskoeffizienten, der aus chemischer Relaxation und der aus Quellungsdaten gewonnene, stimmten sehr gut überein, falls der erstere auf die Dehnung 0 extrapoliert wurde. Die chemische Relaxation des Systems Polyvinylalkohol-Wasser war merklich anders als nach der Theorie erwartet und lie? in erster Linie vermuten, da? der Diffusionskoeffizient von Wasser in diesem Polymeren nicht konstant ist. Eine entsprechende Andeutung wurde aus Quellungsmessungen an diesem System erhalten. Die Diffusion h?ngt von Konzentration und Zeit ab. Aus diesen Resultaten kann gefolgert werden, da? die Technik der Untersuchungen der chemischen Relaxation unter Verwendung einer geeigneten Theorie nicht nur dazu angewendet werden kann, Diffusionskoeffizienten von kleinen Molekülen in einem gegebenen festen Polymeren zu messen, sondern zumindest auch qualitativ den Typ des Quellungsverhaltens festzustellen, der das System unter den gegebenen experimentellen Bedingungen charakterisiert.相似文献
97.
The lipase-catalyzed transesterifications of various substituted diphenyl 1,2-ketals of glycerol have been investigated. Efficient modification of the substrate structure with bis(4-bromophenyl) ketal was found to enhance the enantioselectivity up to E=57 at 0 °C. 相似文献
98.
Ai Suzuki Parasuraman Selvam Tomonori Kusagaya Seiichi Takami Momoji Kubo Akira Imamura Akira Miyamoto 《International journal of quantum chemistry》2005,102(3):318-327
The decomposition reaction dynamics of 2,3,4,4′,5‐penta‐chlorinated biphenyl (2,3,4,4′,5‐PeCB), 3,3′,4,4′,5‐penta‐chlorinated biphenyl (3,3′,4,4′,5‐PeCB), and 2,3,7,8‐tetra‐chlorinated dibenzo‐p‐dioxin (2,3,7,8‐TCDD) was clarified for the first time at atomic and electronic levels, using our novel tight‐binding quantum chemical molecular dynamics method with first‐principles parameterization. The calculation speed of our new method is over 5000 times faster than that of the conventional first‐principles molecular dynamics method. We confirmed that the structure, energy, and electronic states of the above molecules calculated by our new method are quantitatively consistent with those by first‐principles calculations. After the confirmation of our methodology, we investigated the decomposition reaction dynamics of the above molecules and the calculated dynamic behaviors indicate that the oxidation of the 2,3,4,4′,5‐PeCB, 3,3′,4,4′,5‐PeCB, and 2,3,7,8‐TCDD proceeds through an epoxide intermediate, which is in good agreement with the previous experimental reports and consistent with our static density functional theory calculations. These results proved that our new tight‐binding quantum chemical molecular dynamics method with first‐principles parameterization is an effective tool to clarify the chemical reaction dynamics at reaction temperatures. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
99.
Yasuo Kimura Takashi Hamasaki Hiromitsu Nakajima Akira Isogai 《Tetrahedron letters》1982,23(2):225-228
Aszonalenin () has been isolated from together with LL-S490β () and the structure of has been established by spectroscopic evidences and chemical transformation. 相似文献
100.
Kunio Urushido Akira Matsumoto Masayoshi Oiwa 《Journal of polymer science. Part A, Polymer chemistry》1981,19(2):245-256
Radical copolymerizations of methyl allyl maleate (MAM) and methyl allyl fumarate (MAF) with styrene (St) are carried out in bulk using AIBN as an initiator at 60°C, and their copolymerization behaviors are compared in detail. The different rate features are observed with each other; thus in the MAF-St copolymerization the rate was quite enhanced and, also, the maximum rate was found at the molar ratio of 1:1 in the monomer feed, whereas no maximum phenomenon of the rate was apparent for the MAM—St copolymerization. The copolymerizability of MAF with St was quite high, whereas that of MAM was very poor. The cyclization of MAM or MAF was hindered by the highly reactive St monomer. These results are discussed in terms of the formation of the charge—transfer complex between MAF and St and, furthermore, the cyclocopolymerization kinetics involving the 17 elementary reactions as the propagation reactions. 相似文献