共查询到20条相似文献,搜索用时 15 毫秒
1.
The cycloaddition of α,β-epoxyaldehydes or ketones () with the ketene acetal MeHC=C(OMe)2 () gives epoxyoxetanes () in high yields. Without isolation they can be transformed into 4-hydroxy-5-(1-hydroxyalkyl)-γ-butyrolactones () via the epoxy esters and trihydroxy esters (). The lactones appear to be valuable precursors for the synthesis of 5-(1-hydroxyalkyl)-3-methyl-2-5H-furanones () and 3-methyl-5-ylidene-2-5H-furanones () 相似文献
2.
Claudio Fuganti Piero Grasselli Stefano Servi Carlo Zirotti 《Tetrahedron letters》1982,23(41):4269-4272
The C4erythro and threo diols (7) and (8) are converted either into the chiral epoxides (13) and (15) or into the enantiomers (14) and (16); the epoxide (13) is used as chiral synthon for the preparation of (3,4) 4-methyl-3-heptanol (21). 相似文献
3.
The diene reacted with CHCl3/aq. NaOH/PTC in CH2 Cl2 unexpectedly to give a mixture of the chlorination products and . Usual chlorination with Cl2 yielded similarly , , and dependent on the amount of Cl2. The formation of as well as the reaction of to give (besides ) shows an unusual Cl-Cl-interaction. 相似文献
4.
Toshiyuki Yamashita Takeo Fujino Norio Masaki Hiroaki Tagawa 《Journal of solid state chemistry》1981,37(2):133-139
The structural parameters of α- and β-CdUO4 crystals are determined by X-ray powder diffraction technique. α-CdUO4 is rhombohedral and cell parameters are a = 6.233(3) Å and α = 36.12(5)°. β-CdUO4 crystallizes in a C-centered orthorhombic cell with a = 7.023(4), b = 6.849(3), c = 3.514 (2) Å. The space groups are for α-CdUO4 and Cmmm for β-CdUO4. α-CdUO4: 1U in (000), 1Cd in (), 2O(1) in ±(uuu), 2O(2) in ±(vvv); u = 0.113, v = 0.350, Z = 1. β-CdUO4: 2U in (), 2Cd in (), 4O(1) in (), 4O(2) in (); x = 0.159, y = 0.278, Z = 2. β-CdUO4 contains collinear uranyl UO2+2 groups with a UO(1) distance of 1.91 Å, located either along or parallel to the c axis whereas the UO(1) bond length in α-CdUO4 is 1.98 Å which is longer than the usual uranyl bond length. 相似文献
5.
The acid catalysed rearrangement of 8-methyl-pentacyclo(5.4.0.02,6.03,10.05,9)undecan-8-endo-o1 () to 3-methyl-(D3)-trishomocuban-4-o1 () provided the key step to the synthesis of the title compound (). 相似文献
6.
Isao Kawada Mitsuko Nakano-Onoda Motohiko Ishii Masanobu Saeki Mitsuoki Nakahira 《Journal of solid state chemistry》1975,15(3):246-252
Crystal structures of the ordered phases of V3S4 and V5S8 were refined with single crystal data. Both are monoclinic. Chemical compositions, space groups and lattice constants are as follows: VS1.47, (No. 12), a = 5.831(1), b = 3.267(1), c = 11.317(2)Å, β = 91.78(1)° and VS1.64, (No. 12), a = 11.396(11), b = 6.645(7), c = 11.293(4), Å, β = 91.45(6)°. In both structures, short metal-metal bonds were found between the layers as well as within them. In comparison with the structure of Fe7S8, the stability of NiAs-type structure was discussed based on the detailed metal-sulfur distances. 相似文献
7.
Conformational analysis of methylcycloheptanones was achieved by relating CD rotational strengths to conformational free energies. Twist conformers with C1 on the symmetry axis (TC1) were found to be more stable than those with C2 or C7 on the symmetry axis (TC2 or TC7). The free energy differences were found to range from 0.2 to 1.2. A similar analysis of (+)(3R)-methylcyclohexanone showed the equatorial chair conformer to be most stable, by 0.50–0.75 . 相似文献
8.
The crystal structure of the 42-Å subcell of a layer structure with approximate composition Ba4Nb2S9
J.S. Swinnea H. Steinfink L.E. Rendon-Diazmiron M. Gomezdaza 《Journal of solid state chemistry》1983,46(3):367-372
Platy crystals from the products of a mixture 4 Bas : 2 Nb : 5 S reacted at 1000°C have cell constants a = 13.754(3) Å, c = 83.73(2) Å, . The reciprocal lattice had a pronounced subcell with dimensions a = 6.877(1) Å, c = 41.84(1) Å, same space group. Three dimensional X-ray diffraction data were collected using monochromatized Mo Kα radiation and of 5051 measured intensities 1892 were considered observed. From the set of observed intensities 611 reflections having all even indices were used to refine the crystal structure of the 42 × 7-Å subcell. The final R = 0.036 and ωR = 0.052 for the 611 observed amplitudes and R = 0.046, ωR = 0.052 for all 711 amplitudes of the subcell. The structure is based on the stacking of hexagonal BaS3 layers with the sequence DABABDBCBCDCACAD. The D layer denotes a disordered level and occurs at and . The different letters for the ordered layers are based on the Ba positions in that layer. The Nb ions occupy octahedral interstices and form a unit of three face sharing octahedra parallel to c. The column is terminated above and below by disordered levels. The NbNb distances are 3.22 Å, causing displacement of Nb from the centers of the two outside octahedra. One Ba is in the center of a triangular orthobicupola formed by 12 S atoms. The other Ba is in the center of a hexagon of 6 S with 3 additional S above this layer forming of a cuboctahedron. The lower half consists of a disordered layer of atoms. The NbS distances are 2.279, 2.433, and 2.683 Å; BaS distances vary between 3.1 and 3.5 Å. The subcell content based on the ordered structure only is Ba12Nb9S36. The placement of disordered Ba and S at , and levels of the subcell leads to the unlikely composition Ba16.5Nb9S42. The ordered structure most likely has a composition Ba4Nb2S9, z = 36, so that the subcell composition should be Ba18Nb9S40.5. The completely ordered structure has not been solved. 相似文献
9.
The structure of a crystal was established by X-ray analysis. The solution in the cell of symmetry , with a = 6.6702(5), b = 5.3228(8), c = 8.9091(8) Å, β = 100.546(7)°, Z = 1, has led to R = 0.033 and Rw = 0.036 for 2155 reflections with . This structure can be described as two octahedra-wide ReO3-type slabs connected through “planes” of PO4 tetrahedra. A new structural family KxP2W2nO6n+4 can be foreseen which is closely related to the orthorhombic P4W8O32 and the monoclinic RbxP8W8nO24n+16 series. 相似文献
10.
The magnetic interaction in the structural units [Fe2O7]8?, built of two corner-sharing FeO4 tetrahedra, in Na8Fe2O7 () has been studied by magnetic susceptibility measurements (4.2–500 K). An exchange integral of ?37 K is obtained by comparison of the experimental values and the calculated ones using a Heisenberg-Dirac-Van Vleck-type Hamiltonian ? = . The hypothesis of magnetically isolated [Fe2O7]8? groups is corroborated by Mössbauer spectroscopy between 1.5 and 77 K. The susceptibility measurements of the solid solutions Na8Fe2?xMxO7 (M = Al, Ga; 0 ≤ x ≤ 0.2 for Al; 0 ≤ x ≤ 2 for Ga) leads to the same conclusion of the existence of isolated Fe3+Fe3+ pairs in Na8Fe2O7. The type of substitution of Fe by Al or Ga is determined; homonuclear Fe3+Fe3+ and M3+M3+ pairs and heteronuclear Fe3+M3+ pairs are formed. 相似文献
11.
Gennady I. Nikishin Emmanuil I. Troyansky Margarita I. Lazareva 《Tetrahedron letters》1985,26(31):3743-3744
Alkanesulfomides are converted regioselectively into 3-chloroalkane-sulfonamides in one-pot reaction with Na2S2O8-CuCl2. N-Amylbutanesulfonamide is substituted predominantly on sulfonyl moiety. 相似文献
12.
This paper gives an outline of the structure of a solid solution based on 7Bi2O3 · 2WO3. The experimental results using X-ray diffraction methods (precession and powder) showed that 7Bi2O3 · 2WO3 crystallizes in the space group with a = 12.5143(5)Å and c = 11.2248(6) Å. The number of formula weights per unit cell is 40, when the formula is considered to be of the oxygen-deficient fluorite-type Bi0.875W0.125O1.6875. The compound has a substructure based on a defect fluorite-type pseudocubic subcell with Å. The axial relations between the supercell and subcell are and . The solid solution was formed over a limited range of WO3 content between 21.3 mole% and 26.3 mole% at 700°C. The ordering of metal atoms is discussed and an ideal crystal structure is proposed. 相似文献
13.
Conjugate addition of O-silylated ketene acetals to α,β-unsaturated carbonyl compounds in acetonitrile gave quantitative yields of the corresponding β-(alkoxycarbonyl)methyl O-silyl enolates . Site specific electrophilic substitutions of yielded the corresponding α-substituted β-(alkoxycarbonyl)-methylalkanones , , and . 相似文献
14.
2-[(Dimethylamino)methyl]phenylcopper tetramer (R4Cu4) forms a red complex (RCu - CuBr)n with cuprous bromide. The interaction of 2-[(dimethylamino)methyl]phenylcopper with cupric halides results in the formation of the dimer RR, the 2-halo-substituted benzylamine R—Halide and minor amounts of N,N-dimethylbenzylamine RH. The formation of these products can be explained on the basis of an intramolecular electron-transfer redox reaction taking place in innersphere activated complexes of the type R4Cu3Cu - - - X - - - CuIIX(CuIIX2)n-1. The course of the metathesis reaction of 2-[(dimethylamino)methyl]phenyllithium with cuprous bromide depends on the order of addition of the reactants. Reversed addition (RLi to CuBr) results in the formation of an inseparable mixture of complexes of the type (RCu)x- (CuBr)y. Upon addition of CuBr to RLi the uncomplexed organocopper compound R4Cu4 is formed. 相似文献
15.
A large scale synthesis for (-)-3-PPP has been developed. The racemic methoxy compound was prepared in a three step procedure in 63% yield. This was resolved as a diastereomeric salt by crystallization of the (-)-di-p-toluoyltartrate. Two crystallizations gave the pure (-)-enantiomer in 50% of the theoretical yield and with an enantiomeric excess of >95%. Demethylation using aqueous HBr gave (-)-3-PPP, (). Compound was also prepared in a stereoselective synthesis from -(-)- N-propyl-2- chloromethylpyrrolidine . By X-ray crystallography it was shown that (-)-3-PPP has the -configuration at the chiral carbon. 相似文献
16.
Crystals of hexagonal Fe2Mo3O8 up to 3 × 3 × 2 mm were grown by chemical vapor transport from a starting mixture of composition Fe2MoO4. The morphology is {101}, {}, {110}, {}, {100} and corresponds to the absolute orientation of the polar z axis. Both magnetic susceptibility and electrical conductivity show considerable anisotropy. The compound orders antiferromagnetically at 59.5 K, with the spin along c. It is a low-conductivity semiconductor with activation energies 0.14 and 0.21 eV perpendicular and parallel to c, respectively. 相似文献
17.
M.G. Vitovskaya P.N. Lavrenko O.V. Okatova E.P. Astapenko V.B. Novakovsky S.V. Bushin V.N. Tsvetkov 《European Polymer Journal》1982,18(7):583-588
Translational diffusion, velocity sedimentation and viscometry of polyamidobenzimidazole (PABI) solutions in the range of M = (1–61) · 103 have been investigated in N,N-dimethylacetamide (DMA) and 98% H2SO4. The dependences of D0, S0 and [η] on M were obtained. Tsvetkov-Klenin's hydrodynamic invariant was found to be . The equilibrium rigidity of PABI molecules was characterized by the length of the Kuhn segment . The chain diameter was . The values of A in 98% H2SO4 and in an aprotic solvent, DMA, were virtually identical, implying that the rigid-chain conformation of PABI molecules in 98% H2SO4 is due to their geometrical structure rather than to the protonization of amide bonds. The significance of the latter evidently increases in PABI solutions in 100% H2SO4 in which A is 1.5 times as high. The decrease in rigidity of PABI as compared to that of poly-p-phenylene terephthalamide () is in reasonable agreement with the presence of imidazole rings in PABI molecules. The presence of these rings results in kinks in the PABI chain with angles of about 30° and hence, in the depature from parallelism of rotating bonds. 相似文献
18.
Ce2(MoO4)2(Mo2O7) crystallizes in the triclinic system with unit cell dimensions (from single-crystal data) a = 11.903(8), b = 7.509(5), c = 7.385(5) Å, α = 94.33(8), β = 97.41(8), γ = 88.56(7)°, and space group . The structure was solved using Patterson (“P1 method”) and Fourier techniques. Of the 8065 unique reflections measured by counter techniques, 6314 with I ≥ 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.035 (Rw = 0.034). The structure of Ce2(MoO4)2(Mo2O7) consists of dimolybdate chains of the K2Mo2O7 and (NH4)2Mo2O7 type separated by isolated MoO4 tetrahedra and cerium(III) polyhedra. 相似文献
19.
The structure of the compound La4NiS7 has been investigated by the X-ray method. The crystal, which is tetragonal with a = 4.0801 Å and c = 16.334 Å, space group , exhibits superstructure reflections with a′ = 4a, c′ = c, and v′ = 16 v. The structure has been solved with substructure reflections (R = 0.056), the complementary structure reflections being too weak for measurement. This structure is a distorted K2NiF4 type. Lanthanum atoms are in 7–8-fold coordinated sites, one nickel atom is in a distorted octahedral site, and the other nickel atom in a site with coordinance 7. 相似文献
20.
6, 7-Dimethoxy-2-l,3-benzothiazine derivatives (, ) react with substituted acetyl chlorides to give angularly condensed β -lactams (-, , ). The compound was epimerised to the derivative . From the interaction of 2-phenyl-6,7-dimethoxy-4-1,3-benzothiazine () and α -chloro-phenylacetyl chloride two stereoisomeric β -lactam derivatives (, ) were isolated, whereas in the other cases studied the reactions leading to β -lactams proved to be stereospecific. Analogous reactions of -methyl-6,7-dimethoxy-2-l,3-benzothiazine () furnished the enamides ,, . Structures of the new compounds and configurations of the diastereomers were elucidated by IR and NMR spectroscopy. 相似文献