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131.
Kazuo Hara Yukio Imanishi Toshinobu Higashimura Mikiharu Kamachi 《Journal of polymer science. Part A, Polymer chemistry》1971,9(10):2933-2948
1-Vinylcyclohexene (VCH), which has one of the double bonds in the ring and the other outside the ring, was synthesized and polymerized by cationic catalysts. The reactivity of VCH was very large in the polymerizations catalyzed by boron trifluoride etherate (BF3OEt2) and stannic chloride–trichloroacetic acid complex. Similar to other cyclic dienes, the polymerization of VCH was a nonstationary reaction having a very fast initiation step. The polymerization proceeded by either a 1,2- or a 1,4-propagation mode in which vinyl group was always involved. Particularly when BF3OEt2 was used as a catalyst, an intramolecular proton or an intramolecular hydride ion transfer reaction took place, resulting in the formation of methyl groups in the polymer. The degree of polymerization of polymer formed was about 10. This indicates the preponderance of monomer transfer reaction. To investigate the reason for the high reactivity of cyclic dienes, cationic copolymerizations of VCH and 3-methyl-cis/trans-1,3-pentadiene (cis/trans-MPD) was carried out. The relative reactivity of monomers decreased in the order VCH > trans-MPD > cis-MPD. On the other hand, the resonance stabilization of monomers decreased in the order VCH > trans-MPD > cis-MPD. Therefore, it could be considered that the monomer reactivity is mainly determined by the stability of carbonium ion intermediate. The relative stability of carbonium ion must be VCH > trans-MPD > cis-MPD. Thus the influence of the conformation of ion on its stability was clearly demonstrated. 相似文献
132.
Toshinobu Higashimura Yoshitsugu Hirokawa 《Journal of polymer science. Part A, Polymer chemistry》1977,15(5):1137-1143
In order to elucidate the possibility of stereoelective cationic polymerization (asymmetric selective polymerization) of olefinic monomers, racemic cis- and trans-1-methylpropyl propenyl ether and racemic 1-methylpropyl vinyl ether were polymerized by asymmetric alkoxyaluminum dichlorides. In the polymerization of racemic cis-1-methylpropyl propenyl ether with (?)-menthoxyaluminum dichloride in toluene at ?78°C, the polymer obtained showed a positive optical activity, and the residual monomers were converted by BF3OEt2 into a polymer having a negative optical activity. Thus, the stereoelective polymerization of racemic cis-1-methylpropyl propenyl ether was beyond any doubt attained in homogeneous cationic polymerization. In the polymerization of the trans isomer by the same catalyst, an optically active polymer was hardly formed. In the polymerization of racemic 1-methylpropyl vinyl ether which has no β-methyl group, stereoelectivity was not observed at all. The cis-1-methylpropyl propenyl ether did not produce an optical active polymer in the polymerization catalyzed by (S)-1-methylpropoxyaluminum dichloride or (S)-2-methylbutoxyaluminum dichloride under the same polymerization conditions. 相似文献
133.
[reaction: see text] Lipase-catalyzed resolution of (2R*,3S*)-3-methyl-3-phenyl-2-aziridinemethanol, (+/-)-2, at low temperatures gave synthetically useful (2R,3S)-2 and its acetate (2S,3R)-2a with (2S)-selectivity (E = 55 at -40 degrees C), while a similar reaction of (2R*,3R*)-3-methyl-3-phenyl-2-aziridinemethanol, (+/-)-3, gave (2S,3S)-3 and its acetate (2R,3R)-3a with (2R)-selectivity (E = 73 at -20 degrees C). Compound (+/-)-2 was prepared conveniently via diastereoselective addition of MeMgBr to tert-butyl 3-phenyl-2H-azirine-2-carboxylate, (+/-)-1a, which was successfully prepared by the Neber reaction of oxime tosylate of tert-butyl benzoyl acetate 7a. The tert-butyl ester was requisite to promote this reaction. For determination of the absolute configuration of (2S,3R)-2a, enantiopure (2S,3R)-2 was independently prepared in three steps involving diastereoselective methylation of 3-phenyl-2H-azirine-2-methanol, (S)-10, with MeMgBr. The absolute configuration of (2S,3S)-3 was determined by X-ray analysis of the corresponding N-(S)-2-(6-methoxy-2-naphthyl)propanoyl derivative (S,S,S)-13. 相似文献
134.
Tamotsu Hashimoto Etsu Takeuchi Mitsuo Sawamoto Toshinobu Higashimura 《Journal of polymer science. Part A, Polymer chemistry》1990,28(5):1137-1148
Carboxylic acid or primary amine-terminated poly(isobutyl vinyl ethers) were synthesized by living cationic polymerizations with functionalized initiators (CH3CHIO? CH2CH2 ? X; X: that are the adducts of the corresponding vinyl ethers (CH2 ? CH ? OCH2CH2? X) with hydrogen iodide. In the presence of iodine, these initiators induced living cationic polymerization of isobutyl vinyl ether to give polymers with the α-end group of X originating from the initiators. The polymer molecular weights were regulated by the monomer to initiator feed ratio and the molecular weight distributions were very narrow (M w/M n ≤ 1.15). Subsequent deprotection of the terminal group X led to polymers with a terminal carboxylic acid or primary amine. 1H- and 13C-NMR analyses showed that the end functionalities of these polymers were all close to unity. 相似文献
135.
Methyl, ethyl, and isopropyl butenyl ethers, CH3CH2CH?CHOR, were polymerized with homogeneous catalysts at ?78°C. Toluene, methylene chloride, and nitroethane were used as solvents, and BF3O(C2H5)2 and SnCl4·CCl3CO2H were used as catalysts. The stereoregularity of the polymers were compared by x-ray diagrams and infrared absorption ratios. The stereoregularity of polymers increased with increasing content of the trans isomer in the monomer and with increasing polarity of the solvent. In the polymerization of methyl and ethyl butenyl ethers, crystalline polymers were obtained from both the trans and cis isomers. The crystalline polymer prepared from the trans isomer and that from the cis isomer had the same steric structure. This behavior is quite different from that observed in the polymerization of propenyl ethers. It is concluded that the bulkiness of the group on the olefinic β-carbon plays an important role in the stereospecific polymerization of α,β-disubstituted olefins. 相似文献
136.
Toshinobu Korenaga 《Journal of fluorine chemistry》2003,122(2):201-205
Presence of an unique atom-to-face alcoholic oxygen atom?π interaction between a pentafluorophenyl group and alcoholic oxygen (O?π) has been demonstrated by X-ray analysis of the novel chiral amino alcohol instead of the well-known interaction between usual aromatic ring and alcoholic hydrogen atom (OH?π). 相似文献
137.
The iterative extended Hückel method proposed by Harriset al. has been employed to calculate the shapes of 21 molecules consisting of H, C, N, and O. It has given fairly reasonable results, especially when it has been combined with a new formula; the formula regards the orbital energies and the wave functions of the Hückel method as those of the Hartree-Fock method. 相似文献
138.
Murata C Masuda T Kamochi Y Todoroki K Yoshida H Nohta H Yamaguchi M Takadate A 《Chemical & pharmaceutical bulletin》2005,53(7):750-758
To improve the fluorescence characteristics, especially emission wavelength, of coumarins, various 3-substituted-6-methoxycoumarin derivatives were synthesized, and then benzocoumarin derivatives were also synthesized in expectation of the shift to the longer wavelength region by the extension of the conjugated system. Their fluorescence properties were investigated spectrophotometrically in acetonitrile and evaluated from the viewpoint of the intramolecular charge transfer (ICT) between push- and pull-substituents in the ground and the excited states. Among them, benzocoumarin derivatives especially fluoresced in the longer wavelength around 540 nm with remarkably large Stokes shifts beyond 10,000 cm(-1). Using such fluorophores, some novel fluorescence derivatization reagents for carboxylic acids, alcohols, phenols, and amines were preliminarily prepared as an example, and their derivatized products were also found to fluoresce in the longer wavelength region with large Stokes shifts. 相似文献
139.
Rational control of enantioselectivity of lipase by site-directed mutagenesis based on the mechanism
Ema T Fujii T Ozaki M Korenaga T Sakai T 《Chemical communications (Cambridge, England)》2005,(37):4650-4651
The enantioselectivity of a Burkholderia cepacia lipase toward secondary alcohols could be both increased and decreased rationally by introducing only a single mutation on the basis of the mechanism proposed previously. 相似文献
140.
The behavior of copper ions in the Cu2O·Al2O3·4SiO2 (in moles) glass on heating in air at temperatures up to 500°C was studied. When the glass, in which about 90% of Cu was present as Cu+ ions, was heated in air above 300°C, a CuO layer was formed on the surface. The amount of CuO was increased with heating temperature and time, corresponding to the decrease in weight of the glass. Furthermore, the fraction of Cu2+ ions in the glass increased. These observations suggest that oxygens do not diffuse into the glass, but Cu+ ions migrate to the surface from the interior to balance the surplus positive charge produced by the oxidation of Cu+ to Cu2+ ions inside the glass. The following reaction scheme for the formation of the CuO layer was proposed; 2Cu+(interior) + 21O2(surface) → Cu2+(interior) + CuO(surface). 相似文献