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排序方式: 共有619条查询结果,搜索用时 15 毫秒
31.
Masahito Segi Hiroaki Yamamoto Takeyoshi Hori Tadashi Nakajima 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):599-602
Selenoaldehydes and selenoketones, generated by thermal retro-Diels-Alder reaction of their cycloadducts with cyclopentadiene, reacted with oxygen-functionalized conjugated dienes such as 1-acetoxy-1,3-butadiene, Danishefsky's diene, and 1,4-diacetoxy-1,3-butadiene to give the corresponding cycloadducts in good yields regioselectively. 相似文献
32.
Kazuyuki Kubo Hiroshi Nakazawa Hiroyasu Inagaki Tomoyuki Miyake Tsutomu Mizuta Katsuhiko Miyoshi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8-9):2159-2160
Treatment of [Cp*(CO) 2 M{P(NHPh)(OMe) 2 }]PF 6 (M = Fe and Ru) with NaNH 2 gives metallaiminophosphoranes, Cp*(CO) 2 M{P(NPh)(OMe) 2 }. The x-ray structures and reactivity of the complexes are reported. 相似文献
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5-[4-(1-Hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin (1a) and zinc porphyrin 1b were designed and synthesized to experimentally examine the validity of the transition-state model previously proposed for the lipase-catalyzed kinetic resolution of secondary alcohols. The lipases from Pseudomonas cepacia (lipase PS), Candida antarctica (CHIRAZYME L-2), Rhizomucor miehei (CHIRAZYME L-9), and Pseudomonas aeruginosa (lipase LIP) exhibited excellent enantioselectivity (E >100 at 30 degrees C). Subtilisin Carlsberg from Bacillus licheniformis (ChiroCLEC-BL) also showed high enantioselectivity for 1a (E = 140 at 30 degrees C), and the thermodynamic parameters were determined: DeltaDeltaH = -6.8 +/- 0.8 kcal mol(-1), DeltaDeltaS = -13 +/- 3 cal mol(-1) K(-1). Lipases and subtilisin showed R- and S-preference for 1, respectively. The mechanisms underlying the experimental observations are explained in terms of the transition-state models. The large secondary alcohol 1 is a powerful tool for investigating the conformation of the transition state of the enzyme-catalyzed reactions. The fact that 1 was resolved with high enantioselectivity strongly suggests that the gauche conformation, but not the anti conformation, is taken in the transition state, in agreement with the transition-state models involving the stereoelectronic effect. 相似文献
36.
Exposure of tertiary thioamides to (E)-1-hexenyl(phenyl)-lambda 3-iodane results in vinylic SN2 reaction to give the inverted (Z)-S-vinylthioimidonium salts, which under alkaline hydrolysis (Na2CO3 or K2CO3) selectively afford amides, while (Z)-S-vinyl thioesters are obtained in high yields via the hydrolysis under acidic conditions (HCl). 相似文献
37.
Yasuo Tokit Yoshio Inoue Riichir Chûj Yasuhiro Miyoshi 《Magnetic resonance in chemistry : MRC》1975,7(10):485-487
Carbon-13 NMR spectra have been obtained for all-trans-N-retinylidene-n-butylamine as an analogue of the Schiff's base linkage compound in visual pigment. The chemical shift changes on going from all-trans-retinal1 to all-trans-N-retinylidene-n-butylamine are observed. These changes indicate the collapse of the bond alternation in conjugated polyene carbons, whereas N-protonation in all-trans-N-retinylidene-n-butylamine does not affect the bond alternation. 相似文献
38.
Hiroshi Kashiwagi Toshikazu Takada Shigeru Obara Eisaku Miyoshi Kimio Ohno 《International journal of quantum chemistry》1978,14(1):13-27
Ab initio LCAO SCF MO calculations are carried out on planar Co-porphine with a basis set of roughly double zeta quality for Co and N and of single zeta quality for C and H. The net charge on Co and N and the overlap population between them are 1.78, ?0.57, and 0.06, respectively, in the 2A1g, state, which is known to be the ground state by experiment. The bonding in this complex is thus largely ionic. The first and second calculated ionization potentials are 6.51 and 6.77 eV, respectively, and are in reasonable agreement with the observed ionization potentials of 6.44 and 6.62 eV for Ni-tetraphenylporphine. CI calculations within the framework of the ligand field theory are also performed. The calculated order of the five lowest states is 4B2g ≈ 4Eg, 4A2g, 2A1g, 4Eg from below and is not in agreement with the semiempirical order of 2A1g ≈ 4B2G, 4A2g, 2Eg, 4Eg determined by Lin. 相似文献
39.
Cho T Yoshida M Kohagura J Hirata M Numakura T Higaki H Hojo H Ichimura M Ishii K Islam KM Itakura A Katanuma I Nakashima Y Saito T Tatematsu Y Yoshikawa M Kojima Y Tokioka S Yokoyama N Tomii Y Imai T Pastukhov VP Miyoshi S;GAMMA Group 《Physical review letters》2005,94(8):085002
Vortexlike turbulent structures in hot-ion mode plasmas with several keV are observed in the case with a radially produced weak shear of electric fields E(r). However, a strong E(r) shear formation due to a high ion-confining potential phi(c) production clears up these vortices together with plasma-confinement improvement and disappearance of both drift-wave and turbulencelike Fourier spectral signals. These findings are based on three-time progress in phi(c) in comparison to phi(c) attained 1992-2002. The significant advance of phi(c) is well extended in line with proposed potential-formation physics scalings. 相似文献
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