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51.
A new C-8 prenylated 5,7-dimethoxycoumarin named omphamurrayin was isolated from the leaves of Murraya paniculata var. omphalocarpa, and its structure was established as 5,7-dimethoxy-8-(1-oxo-2-senecioyl-3-methyl-3-butenyl)-2H-1-benzopyran-2-one on the basis of the spectroscopic evidence. The taxonomic status of M. paniculata var. omphalocarpa is briefly discussed, along with its synonymity to M. paniculata from the chemosystematic viewpoint. 相似文献
52.
A.F.M. Mustafizur Rahman Motoko Ishibashi 《Journal of organometallic chemistry》2005,690(19):4280-4284
Competitive oxidative chlorination of p-substituted triarylstibines 3 [(p-XC6H4)3Sb; a: X = OMe, c: Cl, d: CO2Et, e: CF3, f: CN, g: NO2] by sulfuryl chloride was carried out against 3b (X = H) and the electronic effect of these substituents on the chlorination of 3 was compared with that of homologous triarylbismuthanes 1. The relative ratios 4/4b (Ar3SbCl2/Ph3SbCl2) decreased with increasing electron-withdrawing ability of the substituents (a: 53/47, c: 49/51, d: 46/54, e: 44/56, f: 40/60, g: 37/63), but the tendency was not so pronounced as observed in the chlorination of 1. A Hammett plot of the 4/4b ratios against the σp constants exhibited a good linear relationship with a negative slope, the value of which was almost half of that deduced from the 2/2b (Ar3BiCl2/Ph3BiCl2) ratios. The difference in the reactivity between 1 and 3 may be explained by the effect of the electron-withdrawing substituents in the aromatic rings, which affects the p-character of the lone pair on the pnictogen atoms by increasing the positive metal charge and appears more remarkably in 1 than in 3. The 13C NMR study of 3 revealed that the chemical shifts of the ipso carbons (C1) attached to the antimony show a linear relationship against the σp constants with a positive slope (14.5). The value was smaller than that deduced from 1 (17.0), suggesting that the antimony center of 3 is less sensitive to the substituent effect. This is in accord with the tendency of the chlorination. 相似文献
53.
54.
N. Mbungu-Tsumbu C. Dauwe M. D. Diatezua L. Mbosei K. Motoko 《Applied Physics A: Materials Science & Processing》1989,48(4):343-346
The relative three-quantum yieldP
3 and the lifetime of ortho-positronium generated by alumina fine powders were studied as a function of temperature and of time. A strong variation in theP
3 value and a constant value of the long lifetime component are interpreted as the existence of two positronium states, one in the interparticle free volume, the second as positronium absorbed to the surface. The latter state is quenched by surface impurities. 相似文献
55.
56.
Kazuo Itoh Masahiko Chikuma Mieko Nishimura Tomoo Tanaka Motoko Tanaka Morio Nakayama Hisashi Tanaka 《Fresenius' Journal of Analytical Chemistry》1989,333(2):102-107
Summary A sulfonic acid derivative of bismuthiol-II (bisIIS) was synthesized from 4-hydrazinobenzene sulfonic acid and carbon disulfide. Selenium(IV) was adsorbed selectively and quantitatively on the anion-exchange resin loaded with bis-IIS. Selenium adsorbed on the resin was eluted by the use of penicillamine and determined by hydride generation atomic absorption spectrometry (hydride generation/AAS). Selenium(VI) and other forms of selenium, which were not adsorbed onto the resin, were collected on the resin after digestion with nitric acid followed by reduction with hydrochloric acid. Separative preconcentration of selenium(IV), selenium(VI) and other forms of selenium in 0.5 mol/l sodium chloride could be carried out successfully by the proposed procedures. However, in the case of estuarial sea water containing a large quantity of organic substances, selenium(IV) could not be separated, because organic substances interfered with the reduction of selenium(VI) to selenium(IV) by the use of hydrochloric acid. Selenium(IV) and total amount of selenium(VI) and other forms of selenium dissolved in polluted sea water samples were determined by the proposed procedures.
Bestimmung von Selen (IV) und anderen in Meereswasser gelösten Selenformen mit Hilfe eines mit dem Sulfonsäurederivat von Bismuthiol-II beladenen Anionenaustauschers und der Hydrid-AAS相似文献
57.
Asano MS Yamashita K Kitabayashi M Kusama K Kagota D Sugiura K 《Physical chemistry chemical physics : PCCP》2011,13(28):12712-12715
The singlet-singlet energy transfer rate in a new zinc(II) porphyrin-free base porphyrin dimer, having a m-bis(phenylethynyl)phenylene bridge, was found to be slower than that in the corresponding p-bis(phenylethynyl)phenylene-bridged dimer, despite the shorter donor-acceptor distance and pathway. The slower rate is interpreted as evidence for a major contribution of the superexchange mechanism. 相似文献
58.
A phenylselenenyl chloride (PhSeCl)-mediated allylic oxidation to give allylically rearranged alcohol has been developed. A possible mechanism for the present reaction is generation of allylic selenide from prenyl moiety via [1,3]-sigmatropic rearrangement, followed by oxidation and [2,3]-sigmatropic rearrangement to afford 3-isopenten-2-ol. 相似文献
59.
Laser flash induced spin-polarized transient electron paramagnetic resonance (TREPR) spectra for vanadyl octaethylporphyrin in isotropic and partially ordered frozen solutions are presented and compared with corresponding luminescence data. The TREPR spectra show well-resolved hyperfine couplings to the vanadium nucleus and a multiplet polarization pattern with features typical of zero-field splitting (ZFS). The principal values of the vanadium hyperfine coupling tensor evaluated from the spectra are 1/3 of the corresponding values found from steady-state EPR spectra of the ground state. On the basis of these characteristics and numerical simulations, the polarization patterns are assigned to the excited quartet state. The values of the ZFS parameters of the trip-quartet obtained from simulation of the spectra (D = 17.5 mT and E = 1.5 mT) are comparable to those of the triplet state of the zinc and free base octaethyl porphyrin. The lifetime of the spin polarization is found to be temperature dependent and is essentially the same as that of the optical emission. The temperature dependence is rationalized using a model in which the decay to the ground state occurs from both the trip-quartet and trip-doublet, which are in thermal equilibrium even at 15 K. A fit of the model to the observed spin polarization lifetimes yields an energy gap of 47 cm(-1) between the trip-quartet and trip-doublet. It is shown that the spin polarization evolves from a multiplet pattern at early times to a net absorptive pattern at late times following the laser flash. It is proposed that the establishment of thermal equilibrium leads to the evolution of the spin from multiplet to net polarization. 相似文献
60.
An Eells-Sampson type theorem for harmonic maps from a finite weighted graph is employed to characterize the equilibrium configurations of crystals. It is thus observed that the mimimum principle frames symmetry of crystals.