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81.
Mao-Peng Lin Haeng-Boo Kim Tomiki Ikeda Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》1992,30(11):2365-2369
Benzyl cation was detected by transient absorption spectroscopy with a spectroscopic multichannel analyzer on pulse excitation (fourth harmonic of Nd:YAG laser, 266 nm; 10 ns fwhm) of benzyl(4-hydroxyphenyl) methylsulfonium hexafluoroantimonate(BSS) in 1,2-dichloroethane (EDC). The benzyl cation was long-lived (lifetime, 59 ms) at room temperature and quenched by a vinyl ether compound. The formation of the benzyl cation as active species on photolysis of BSS is in contrast to the formation of Brønsted acids in other sulfonium salts so far reported. © 1992 John Wiley & Sons, Inc. 相似文献
82.
It has been shown by a series of experiments on 5-alkyl, 5-halo-, and other 5-substituted 1-naphthol derivatives that the product ratio of the ortho- and para-naphthoquinones formed on oxidation with Fremy's salt is controlled by the bulkiness of the C5-substituent. 相似文献
83.
We report herein a practical synthesis of 4'-thiothymidine (15) and appropriately protected 2'-deoxy-4'-thiocytidine (16), -thioadenosine (27), and -thioguanosine (29) derivatives, substrates for the synthesis of 4'-thioDNA, from the corresponding 4'-thioribonucleosides. 2'-deoxy-4'-thiopyrimidine nucleosides were synthesized using a radical reaction of the corresponding 2'-alpha-bromo derivatives, which were prepared via 2,2'-O-anhydro derivatives. 2'-deoxy-4'-thiopurine nucleosides were synthesized using the same radical reaction of the corresponding 2'-beta-bromo derivatives. 相似文献
84.
Nishinaga T Yamazaki D Stahr H Wakamiya A Komatsu K 《Journal of the American Chemical Society》2003,125(24):7324-7335
Novel cyclopentadienyl (Cp)-alkali metal complexes 1-M and 2-M (M = Li, Na, K), in which the Cp ring is annelated with two bicyclo[2.2.2]octene units and substituted with a phenyl group for 1 and a tert-butyl group for 2, were synthesized, and their structures and dynamic behaviors were investigated by means of X-ray crystallography, dynamic (13)C NMR, and DFT calculations. The X-ray crystallography results indicated that 1-Li, 1-Na, and 2-Na form monomeric contact ion pairs (CIP) with three THF molecules coordinated to the metal atom. Also, in THF-d(8), all of the 1-M and 2-M form monomeric CIP in the ground state. However, variable-temperature (13)C NMR measurements of 1-M and 2-M in THF-d(8) demonstrated dynamic behavior in which the metal ion exchanges positions between the upper and lower faces of the Cp ring. From a study of the concentration dependence of the dynamic behavior, the exchange was found to proceed principally as an intramolecular process at concentration ranges lower than 0.2 M. The experimentally observed deltaG values for the intramolecular exchange process for all the 1-M and 2-M (except for 2-Li, whose intramolecular process was too slow to observe) were found to be quite similar in THF-d(8) solution and to fall within the range of 12-14 kcal mol(-)(1). Within this range, a tendency was observed for the deltaG values to increase as the size of the metal decreased. Theoretical calculations (B3LYP/6-31G(d)) afforded considerably large values as the gas-phase dissociation energy for 1-M (162.7 kcal mol(-)(1) for M = Li; 131.6 kcal mol(-)(1) for M = Na; 110.9 kcal mol(-)(1) for M = K) and for 2-M (170.0 kcal mol(-)(1) for M = Li; 137.5 kcal mol(-)(1) for M = Na; 115.4 kcal mol(-)(1) for M = K). These values should be compensated for by a decrease in the solvation energies for the metal ions with increasing size, as exemplified by the calculated solvation energy for M(+)(Me(2)O)(4), which serves as a model for metal ions solvated with four molecules of THF (-122.9 kcal mol(-)(1) for M = Li; -94.7 kcal mol(-)(1) for M = Na; -67.7 kcal mol(-)(1) for M = K). This compensation results in a small difference in the overall energy for dissociation of 1-M or 2-M in ethereal solutions, thus supporting the similar deltaG values observed for the intramolecular metal exchange. 相似文献
85.
Masao Ikeda Takashi Nakamura Yu Nagase Koji Ikeda Yoshiro Sekine 《Journal of polymer science. Part A, Polymer chemistry》1981,19(10):2595-2607
For the purpose of studying the mechanism of thermal degradation of poly[(tetramethyl-p-silphenylene) Siloxane] (poly TMPS) a series of polymers with silphenylene and siloxane bonds in the main chain were prepared and subjected to thermogravimetry (TG) and pyrolysis study. Analyses of products from poly TMPS degradation (in vacuum at a constant temperature) by gas chromatography (GC), infrared (IR), nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography-mass spectrometry (GC–MS) revealed that degradation occurs at the silphenylene bonds. The TG curves obtained in He for heating rates of 1,2,2.5,7.5, and 10°C/min were analyzed by the Ozawa method; activation energies of 39 ± 1 and 45 ± 2 kcal/mol were obtained respectively for the initial cleavage of the methyl side group and the later-stage scission of the main-chain silphenylene bond which leads to a major weight loss. The results agree with those obtained for other structurally similar polymers. 相似文献
86.
Mori M Saito N Tanaka D Takimoto M Sato Y 《Journal of the American Chemical Society》2003,125(19):5606-5607
Novel alkenylative cyclization of enyne was developed using Cp*RuCl(cod) under ethylene gas at room temperature. 相似文献
87.
T Oh-Hara Y Ikeda H Sakagami K Konno T Kaiya K Kohda Y Kawazoe 《Chemical & pharmaceutical bulletin》1990,38(1):282-284
We have found that water-soluble extracts of lignified natural products are strong potentiaters of hemolytic plaque-forming cell production in mice. Apparently, the active components involved belong to a lignin family. Consequently, study of medicinal potential, especially immunopotentiating capacity, of lignified materials is important. 相似文献
88.
New synthetic methods for the preparation of 1,3-dienes are described. 相似文献
89.
Porphyrin macrocycles composed of five and six units of m-gable imidazolylporphyrinatozinc (1-Zn) were synthesized by self-assembled cyclization followed by ring-closing metathesis linkings. Each porphyrin macrocycle was isolated by GPC chromatography, and their molecular weights were determined by MALDI-TOF mass spectroscopy. These structures represent mimics of light-harvesting complexes in photosynthetic bacteria. [structure: see text] 相似文献
90.
An epoxy-group-containing polymer chain was grafted onto the hollow-fiber form of a porous polyethylene membrane by the immersion of the electron beam-irradiated trunk polymer in glycidyl methacrylate diluted with methanol and 1-butanol. The epoxy group density ranged from 8.5 to 13.4 mol per kg of the trunk polymer. Subsequently, the epoxy groups produced were converted into sulfonic acid and diethylamino groups. The density of -SOH and -N(C2H5), groups was 0.40 and 2.2 mol per kg of the product. respectively. The polymer brush, defined as a polymer chain extending from the surface of a pore toward the interior of the pore, was evaluated from the determination of an equilibrium binding capacity of hen egg lysozyme (HEL) and bovine serum albumin (BSA). The polymer brush prepared in 1-butanol was found to be longer than that prepared in methanol from the determinations of liquid permeability and protein adsorptivity. The proteins were bound to the polymer brush prepared in 1-butanol, followed by the functionalization, at higher degrees of multilayer binding: about 30 for HEL and 6 for BSA. 相似文献