摘要:

AbstractNew rare earth vanadates YSr2‐xCaxCaxV3O9‐y(x—0.0, 0.67, 1.0, 1.33 and 2.0) have been synthesized by a new simple method. X‐ray powder diffraction results show that they are mono‐phase. They belong to orthorhombic structure and their lattice constants are calculated. The results of weight gains in TG curves show that the lower valent vanadium is oxidized to higher valent state at higher temperature. The oxygen contents of new compounds are calculated from the weight gains. Both V3+and V4+coexist in YSr2‐xCaxV3O9‐y.These compounds exhibit low electric resistivity at roo

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080402

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract8,8′‐Dibromo‐6,6′, 7,7′‐tetramethoxy‐5,5′‐diisopropyl‐3,3′‐oxydimethylene dinaphtho[2,1‐b:2′, 1′‐dlfuran, C32H30Br2*; M.W. = 670; triclinic; space groupP1;a= 8.896(2),b= 10.216(1),c= 10.423(1)Å,a= 108.48(1), β = 119.36(1); γ = 99.26(1); V = 723.5 Å3;Z= 1,Dcal.= 1.479 g.cm−3.MoKα = 28.11 cm−1,F(000) = 326,T= 293 K. The structure was solved by direct method and full‐matrix least‐squares refinement converged atR= 0.034 for 2377 observed reflections. The oxygen atom in seven‐membered ring exists in a disordered arrangement. Both bisnaphthalene and oxygen‐containing five‐membered ring have planar conformations with

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080403

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe surface composition and electronic structure of tungsten carbides prepared by direct synthesis and carburization of white tungstic acid were studied with X‐ray photoelectron spectroscopy. The experimental results show that WO3and free carbon are present on the surface of the carbides. For the high surface area tungsten carbide prepared from white tungstic acid a large extent of oxygen insertion into the crystal lattice was observed. Measurements of the binding energies of the W4f7 2, C1Sand O18core levels indicate that charge transfer is from the W to the C and O atoms, forming W5d‐C3pand W5d‐O2pbonding. The catalytic behavior of the tungsten carbides in hydrocarbon conversion reactions is mentioned and compared with Pt cata

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080404

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe infrared multi‐photon dissociation (IRMPD) of acetic anhydride to generate state‐selected CH2has been investigated by using time and wavelength resolved fluorescence techniques. It has been observed that the generation of the nascent ground state CH2(a1A1) is delayed by about 0.6 μ relative to the onset time of the excited CH2(b1B1). The relative population of the ground and excited state CH2and the onset time for the appearance of the ground state CH2have been found to depend strongly on CO2laser output fluences. These results appear to have a strong bearing on the structure of the potential energy surfaces of the intermediate CH2CO. A possible photolysis mechanism is proposed to explain these experimental res

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080405

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA uranyl compound, K4UO2(CO3)3has been characterized by powder X‐ray diffraction method. M.W. = 606.46, monoclinic,C2/c(No. 15),a= 1.0240(7),b= 0.9198(4),c= 1.2222(12) nm, β = 95.12 (4)°,V= 1.1466(5) nm3,Z= 4,D= 3.468 g/cm3,Dc= 3.513 g/cm, λ(Cu Ka1) = 0.1540598nm,T= 298K. The structure was solved by heavy atom method and Fourier synthesis, and refined by full‐matrix least‐squares method toR= 0.1185 for 275 reflections. The uranium (VI) atom is in an eight‐coordinate distorted hexagonal‐bipyramidal environment with creasy fan shape. The linear uranyl group approaches to perpendicular to the equatorial plane in which three carbonate groups are chelated. U(VI) has two linear oxygen atoms closer to it (U]—0 = 0.1767 (5) nm) than six other neighbours (U—O ranging from 0.2516 to 0.2568 nm). The distances between carbon atoms and uncoordinated oxygen atoms are 0.122 (1) and 0.123(1) nm, which are distinctly different from those between carbon and coordinated oxygen atoms (mean 0.134(6) nm). This fact reveals the non‐equivalence of one oxygen atom to the other two in each carbonate. In K4UO2(CO3)3, the O—O distance for the adjacent carbonate groups is 0.2794(4)nm approaching to the sum of Van der Waals radii of two oxygen atoms. The K—O distances vary between 0.2667 and 0.3131 nm, and each anion is immediately surrounded by six potassium ions, only four of which can be considered to belong to the same structural formula unit, and they are symmetrically located above and belo

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080406

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract1,2‐rearrangements of carbenes: CCH2X(X = CH2, NH and O) are studied by usingab initiogradient method. Heteroatoms N and O stabilize the carbene and decrease its reactivity, mainly by changing frontier molecular orbitals, but retain the way of the reaction. The reaction starts from the attack of the migrating hydrogen on the carbene p AO and ends with the entrance of the hydrogen into the carbene σ orbital. Reactivities are in the order of X = CH8>NH>0. The reaction is exothermic or endothermic according to whether the product is a 4n+2 or 4nπ electron molec

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080407

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe NMR methods (including1H NMR,13C NMR, variable temperature method and the novel ID EXSY technique) were employed to study the conformation of azacrown ethers 1—5 in solution. There are two classes of conformation in which the azacrown ethers exist in solution according to their molecular structure. Two kinds of intramolecular motion of the azacrown ethers were observed, one is the vibration of the macrocyclic ring and the other is its inversion. The ether rings which contain oxygens are more flexible than that constructed by nitrogens in the present case because of the tetrahedron structure of the nitrogen atoms and the hindrance of the groups Ts connected to the nitrogens. Some thermodynamical parameters of the ring inversion process were obtaine

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080408

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractFour 1, 2, 3‐trisubstituted imidazolinium iodides which were used as 5,10 ‐+CPh‐THF model (7—10) at formic acid oxidation level were synthesized. The benzylidyne group (phenyl‐substituted one carbon unit) transfer reactions from these compounds to Grignard reagent were investigated, and the reactions of these compounds with KBH4and NaOH were als

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080409

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe fluorescence quenching of naphthalene (2) and 1,3‐di(α‐naphythyl)propane (1) by RNA and bases in methanol‐water (v:v = 1:1) binary solvents in the presence or absence of cyclodextrin (CD) has been investigated. The results show that both the monomer and excimer fluorescence of 1 can be quenched by these quenchers. The quenching and rates depend on the quencher and temperature. It is shown that there is a critical temperature (Tc) for each quencher. BelowTc, the excimer fluorescence spectra show vibrational structures and the Stern‐Volmer plots are straight lines (for uracil and cytosine); while above theTc, the vibrational structures disappear and the Stern‐Volmer plots deviate from linearity and curve upward. The former is a static process; while the latter is a mixture of both static and dynamic processes. The addition of α‐CD has no effect on the fine structure; whereas β‐CD prevents the appearance of this structure efficiently. The quenching rates both for the monomer and excimer of1by bases except cytosine in the presence of β‐CD at ambient temperature are not changed; the quenching of fluorescence of1by RNA in the presence of β‐CD, however, is hindered. Time‐resolved fluorescence study shows that the excimer fine structures appear from the zero time. The intensity of fine structures depend on the fraction of water (π) in binary solvents, and it is independent of the pH value of the solvents. It is suggested that bases and RNA induced aggregates (perhaps microcrystal) are formed, in which the motio

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080410

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractReaction of perfluoroalkyl iodides with a series of alkynes under sulfinatodehalogenation condition gave a mixture ofE/Zadducts very readily in high yield, thus constituted a mild, convenient and effective new method for the addition of perfluoroalkyl iodides to alkynes. Under the same condition, in the presence of 1‐hexyne perfluoroalkyl bromide and 1,1,1‐trichlorotrifluoroethane reacted only to give sulfinates as the major products. A radical mechanism was proposed for the addition react

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080411

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY