共查询到20条相似文献,搜索用时 31 毫秒
1.
Hong-Wen Hu Xu-Dong Wei Cun Li Hong-Zhe Sun Yi-Ming Yao Zhong-Yuan Zhou Kai-Bei Yu 《中国化学》1992,10(3):278-284
The reaction of m-chlorobenzaldoxime dehydrodimer with styrene gives two 1:1 adducts.The main product 7 is a bisnitrone. The minor product 8 has been shown by X-ray diffraction anal-ysis to possess the structure: ArCH(N=O)CH_2CH (Ph)O--N=CHAr. The two C=N bonds areall in Z configuration. The structure of the adducts from benzaldoxime dehydrodimer and styrene isalso assigned. 相似文献
2.
Fluorotricyanomethane is prepared from potassium tricyanomethanide and perchlorylfluoride. The crystal structure of this compound (orthorhombic, space group P212121, with a=6.270, b=6.734, c=11.776 Å) has been determined by X-ray analysis. The results are discussed in relation to those of (NC)3C? X (X=? CH3, ? Cl, ? Br or ? CN). 相似文献
3.
Siritanon T Li J Stalick JK Macaluso RT Sleight AW Subramanian MA 《Inorganic chemistry》2011,50(17):8494-8501
Structures of CsTe?O(6-x) phases were investigated by single-crystal X-ray diffraction and neutron powder diffraction. Stoichiometric CsTe?O? is a mixed-valence Cs?Te??Te???O?? compound with a rhombohedral pyrochlore-type structure where there is complete order of Te?? and Te??. On heating, this compound develops significant electrical conductivity. As CsTe?O? becomes oxygen deficient above 600 °C, the rhombohedral pyrochlore-type structure is replaced by a cubic pyrochlore-type structure with disordered Te??/Te?? and oxygen vacancies. However, for CsTe?O(6-x) phases prepared at 500 °C, the observed pyrochlore-type structure has symmetry. The Te?? and O vacancies are all on chains running along the b axis, and the maximum value of x observed is about 0.3. At still higher values of x a new compound was discovered with a structure related to that reported for Rb?Te???Te???O??. 相似文献
4.
van Bokhoven JA van der Eerden AM Prins R 《Journal of the American Chemical Society》2004,126(14):4506-4507
The structural changes of the catalytic active site that occur during catalytic reaction in an acidic zeolite are detected. The local structure of the zeolitic Br?nsted active site is a distorted tetrahedrally coordinated aluminum that has three short and one long aluminum-oxygen bond. Using in situ Al K edge X-ray absorption spectroscopy, the adsorption of a reactive intermediate in the oligomerization of ethene changed the local structure of the catalytic active site; the long aluminum oxygen bond is partially relaxed. At increasingly higher temperature, extensive coking of the catalyst frees the Br?nsted acid site from the reactive intermediate, restoring the asymmetric coordination. These measurements show that application of in situ Al K edge spectroscopy provides fundamental insight into the structure of zeolitic catalytically active sites during catalytic action. 相似文献
5.
The structure of 2-hydroxymethylpyridine N-oxide was determined from X-ray diffractometer data by a direct method. The compound crystallizes in the monoclinic space group P21/c with cell dimensions a = 7.079, b = 8.046, c = 10.599 Å, cosβ = ?0.2252. A total of 1241 independent reflections were refined to an R value of 0.06. The N-O dative bond has a length of 1.321 Å and the dative oxygen is bonded to a hydroxyl group on a symmetry related molecule by an inter-molecular hydrogen bond. The structure corroborates recent findings concerning the relationship between the strength of hydrogen bonding to a dative oxygen and the length of the N? O dative bond. 相似文献
6.
The crystal structure of the CL-20 solvate with ?-caprolactam in the 1:6 ratio is obtained and studied. 相似文献
7.
Unverfehrt L Ströbele M Glaser J Langer T Hoffmann RD Pöttgen R Meyer HJ 《Inorganic chemistry》2011,50(13):6010-6018
The new europium fluoride carbodiimide Eu(4)F(5)(CN(2))(2) was synthesized by solid state reaction from mixtures of EuF(3) and Li(2)(CN(2)) at 700 °C. The crystal structure as refined by single crystal X-ray diffraction (P ?42(1)c, no. 114, a = 16.053(1) ?, c = 6.5150(6) ?, Z = 8) reveals three crystallographically distinct [N═C═N](2-) ions in the structure of mixed-valent Eu(4)F(5)(CN(2))(2). The presence of one Eu(3+) and three Eu(2+) per formula unit Eu(4)F(5)(CN(2))(2) is confirmed by magnetic measurements and (151)Eu-Mo?ssbauer spectroscopy. The arrangement of Eu ions and gravity centers of [NCN](2-) ions in the structure of Eu(4)F(5)(CN(2))(2) follow the motif formed by atoms in the CuAl(2)-type structure. A possible high-symmetry structure of Eu(4)F(5)(CN(2))(2) is discussed on the basis of a group-subgroup scheme. 相似文献
8.
The sequences of 13 tryptic peptides of cow ?A-casein (accounting for about one half of the amino acid residues present in the protein) were established. The rennin sensitive linkage could be located in a large fragment (36 residues). ?-casein consists of a hydrophilic part (?-caseino-glycopeptide) and of a hydrophobic moiety (para-?-casein); in this latter, however, several quite hydrophilic sequences were characterized. Another feature of the ?-casein structure is the frequent duplication or triplication of certain amino acids (Pro-Pro; Phe-Phe; Gln-Gln-Gln-Asn-Glu-Glu-Glu; Pro-Pro-Lys-Lys-Asn-Gln-; etc. …). 相似文献
9.
The synthesis of the first alkynyltelluronium salt is presented. X-ray investigations of this species reveal a two-dimensional polymeric structure, assembled through various secondary Te?Te and Te ?I interactions. The structure itself can be rationalized in terms of p→σ* interactions. 相似文献
10.
John R. Günter 《Journal of solid state chemistry》1980,35(1):43-49
Thermal dehydration of copper(II) formate tetrahydrate leads to a modification of the anhydrous salt different from that produced by direct preparation of the latter. As the dehydration is a topotactic process, the known crystal structure of the tetrahydrate and the topotactic orientation relations can be used to deduce the crystal structure of the product. Single-crystal X-ray diffraction patterns of decomposed pseudomorphs yield the following unit cell for the dehydrated formate: monoclinic, a = 8.195 ? 0.006 Å, b = 7.925 ? 0.006 Å, c = 3.620 ? 0.005Å, β = 122.21 ? 0.09°, probable space group . The structure contains copper formate layers very similar to those in the tetrahydrate, stacked in such a way that columns of distorted coordination polyhedra, linked by formate bridges, are formed. The topotactic dehydration occurs in such a way that two-dimensional elements of the structure are unaltered but the mode of stacking is changed. 相似文献
11.
12.
Honda S Akiba T Kato YS Sawada Y Sekijima M Ishimura M Ooishi A Watanabe H Odahara T Harata K 《Journal of the American Chemical Society》2008,130(46):15327-15331
What is the smallest protein? This is actually not such a simple question to answer, because there is no established consensus among scientists as to the definition of a protein. We describe here a designed molecule consisting of only 10 amino acids. Despite its small size, its essential characteristics, revealed by its crystal structure, solution structure, thermal stability, free energy surface, and folding pathway network, are consistent with the properties of natural proteins. The existence of this kind of molecule deepens our understanding of proteins and impels us to define an "ideal protein" without inquiring whether the molecule actually occurs in nature. 相似文献
13.
The originally proposed structure (2) of landomycinone, the aglycone of landomycin A, has been synthesized and shown to be nonidentical to the naturally derived landomycin A aglycone. The synthesis of 2 features the D?tz benzannulation reaction of chromium carbene 5 and alkyne 6, and the intramolecular Michael-type cyclization reaction of the phenolic naphthoquinone 20. It is proposed that natural landomycinone possesses the alternative structure 3, but attempts to access this structure via the Michael-type cyclization of the isomeric phenolic naphthoquinone 38 have been unsuccessful. 相似文献
14.
Ichiro Tajima Minoru Yamamoto 《Journal of polymer science. Part A, Polymer chemistry》1985,23(3):615-622
A plasma-polymerized material was produced from hexamethyldisiloxane vapor by a glow discharge polymerization technique. Spectroscopic interpretation of the chemical structure of the polymerized hexamethyldisiloxane was studied by spectroscopic means such as IR, XPS, and NMR. The plasma polymer was barely soluble in the usual organic solvents, although it contained a small amount of the monomer and its oligomers. The IR spectrum indicated that the polymer consisted of Si? CH3, Si? O, Si? CH2, and Si? H groups. The surface of the polymer was found to retain structural units similar to the monomer from the XPS measurement. On the other hand, the 13C and 29Si high-resolution, solid-state NMR measurements revealed that the plasma polymer was highly crosslinked with a variety of conformations and a number of O atoms surrounding a Si atom. Results from the XPS and NMR spectra suggested that the bulk of the polymer was more oxidized than the surface layer; Si atom was preferentially oxidized. A hypothetical chemical structure was proposed for the polymerized hexamethyl-disiloxane. 相似文献
15.
V. Sydorchuk W. Janusz S. Khalameida E. Skwarek J. Skubiszewska-Zi?ba R. Leboda V. Zazhigalov 《Journal of Thermal Analysis and Calorimetry》2012,108(3):1009-1016
Deposited zirconium phosphate samples on the base of silica and titania have been prepared using the sol?Cgel and mechanochemical methods. Porous structure, phase composition, and electrokinetic parameters have been studied by means of nitrogen adsorption?Cdesorption, XRD, DTA-TG, FTIR, electrophoresis, and potentiometric titration. The compositions possess varied parameters of porous structure, structure of deposited phase, and electrokinetic properties depending on support nature and synthesis conditions. 相似文献
16.
A. N. Chekhlov T. M. Kasumov V. K. Brel N. S. Zefirov 《Journal of Structural Chemistry》1996,37(5):800-806
Crystal and molecular structure of μ-oxo-bis[trifluoroacetato(p-tolyl)iodine] (I) synthesized by a new procedure was determined by X-ray diffraction analysis. Crystals I are orthorhombic, unstable, space group Pbcn, a=17.684(3), b=8.453(3), c=30.560(4) Å, Z=8. The structure of I was solved by direct and Fourier methods and refined by the full-matrix least-squares procedure in an anisotropic-isotropic approximation to R=0.098 (CAD-4 automatic diffractometer, λCuKα, 1200 observed reflections with I≥2σ). In molecule I, two iodine atoms have T-configuration of valence bonds with the average bond angles O?I?O 169(1) and O?I?C 86(2)°, average bond lengths I?Oμ 2.009(9), I?Oacet 2.269(9), and I?Caryl 2.11(1) Å, and the bond angle I?O?I 118.1(5)°. In molecule I, two p-Tol substituents are directed to approximately the same side of the medium plane of the central O?I?O?I?O fragment. Crystal structure I has I...O type intra-and intermolecular nonvalent interactions (secondary bonds). 相似文献
17.
Z.
k 《无机化学与普通化学杂志》1980,460(1):81-85
The structure of monoclinic Se2O5, S. G. P21/c, Z = 4, was solved by direct methods and refined by an anisotropic full matrix least-squares to R = 0.116 for 855 densitometer intensities. The structure consists of zig-zag chaines [? Se(O)? O? Se(O)2? O? ]n with alternating Se(IV) and Se(VI) atoms. Each Se atom is coordinated tetrahedrally, Se(VI) by 4 O atoms, Se(IV) by 3 O atoms and a lone electron pair. 相似文献
18.
Versmold H Musa S Kubetzki H Urban V 《Langmuir : the ACS journal of surfaces and colloids》2005,21(10):4324-4327
In this paper, the ordering in concentrated charge stabilized colloidal dispersions is considered. Despite the impressive Bragg reflections obtained for shear ordered dispersions by light (LS), small-angle neutron (SANS), and small-angle X-ray scattering (SAXS), a number of open questions remain. Sheared dispersions are usually ordered in layers. For such systems, two questions arise: (1) What is the structure in a layer? (2) What is the stacking structure perpendicular to the layers? The second question requires a method to determine the structure perpendicular to the layers. Although originally interested only in structural aspects, we were forced to consider different methods. Two methods are treated both applicable to neutron and X-ray scattering from concentrated dispersions. One has been used by physicists and chemists for many years to determine the structure of crystals by sample rotation. In colloid science, we have used it previously in neutron and X-ray scattering. A second method is treated here which can be applied in small-angle scattering from a Couette cell. It gives the scattering intensity in a certain direction without sample rotation. Although very useful with the Couette cell, it cannot be found in any of the well-known references on colloid science. A theoretical explanation and experimental examples obtained by synchrotron X-ray scattering from a Couette cell are given in the paper. 相似文献
19.
The ternary compound LiInTe2, synthesized by direct reaction of the elemental components, crystallizes in the tetragonal chalcopyrite structure (space group I4 2d) with lattice parameters a = 0.6419(2) and c = 1.2486(3) nm. LiInTe2 remains in the chalcopyrite structure up to the melting temperature of (935 ± 5) K. Infrared reflectance spectra measured in the wavenumber range from 40 to 4000 cm?1 yield two infrared active optical modes. An analysis of the mode frequencies in terms of the Keating model shows that the Li? Te bond is considerably weaker than the In? Te bond. 相似文献
20.
Bylaska EJ Glaesemann KR Felmy AR Vasiliu M Dixon DA Tratnyek PG 《The journal of physical chemistry. A》2010,114(46):12269-12282
Electronic structure methods were used to calculate the gas and aqueous phase reaction energies for reductive dechlorination (i.e., hydrogenolysis), reductive β-elimination, dehydrochlorination, and nucleophilic substitution by OH? of 1,2,3-trichloropropane. The thermochemical properties ΔH(f)°(298.15 K), S°(298.15 K, 1 bar), and ΔG(S)(298.15 K, 1 bar) were calculated by using ab initio electronic structure calculations, isodesmic reactions schemes, gas-phase entropy estimates, and continuum solvation models for 1,2,3-trichloropropane and several likely degradation products: CH3?CHCl?CH2Cl, CH2Cl?CH2?CH2Cl, C?H2?CHCl?CH2Cl, CH2Cl?C?H?CH2Cl, CH2═CCl?CH2Cl, cis-CHCl═CH?CH2Cl, trans-CHCl═CH?CH2Cl, CH2═CH?CH2Cl, CH2Cl?CHCl?CH2OH, CH2Cl?CHOH?CH2Cl, CH2═CCl?CH2OH, CH2═COH?CH2Cl, cis-CHOH═CH?CH2Cl, trans-CHOH═CH?CH2Cl, CH(═O)?CH2?CH2Cl, and CH3?C(═O)?CH2Cl. On the basis of these thermochemical estimates, together with a Fe(II)/Fe(III) chemical equilibrium model for natural reducing environments, all of the reactions studied were predicted to be very favorable in the standard state and under a wide range of pH conditions. The most favorable reaction was reductive β-elimination (ΔG(rxn)° ≈ ?32 kcal/mol), followed closely by reductive dechlorination (ΔG(rxn)° ≈ ?27 kcal/mol), dehydrochlorination (ΔG(rxn)° ≈ ?27 kcal/mol), and nucleophilic substitution by OH? (ΔG(rxn)° ≈ ?25 kcal/mol). For both reduction reactions studied, it was found that the first electron-transfer step, yielding the intermediate C?H2?CHCl?CH2Cl and the CH2Cl?C?H?CH2Cl species, was not favorable in the standard state (ΔG(rxn)° ≈ +15 kcal/mol) and was predicted to occur only at relatively high pH values. This result suggests that reduction by natural attenuation is unlikely. 相似文献