共查询到20条相似文献,搜索用时 15 毫秒
1.
Gösta Brunow Pirkko Karhunen Knut Lundquist Solveig Olson Rolf Stomberg 《Journal of chemical crystallography》1995,25(1):1-10
Lignin models of the biphenyl type have been synthesized and crystal structures of two of them have been determined. The tetraacetate of 5,5-bis(hydroxymethyl)-3,3-dimethoxy-2,2-biphenyldiol crystallizes in space group
witha=11.319(2),b=12.232(6),c=9.242(3) Å, =101.66(3)°, =108.14(2)°, =79.08(2)° andZ=2.R=0.036 (2720 observed [I>3(I)] reflections). The acetate of 5,5-di-tert-butyl-2,3,3-trimethoxy-2-biphenylol crystallizes in space group
witha=11.972(2),b=21.621(3),c=9.834(1) Å, =91.18(1)°, =113.13(1)°. =98.42(1)°, andZ=4.R=0.050 (8129 observed [I>3(I)] reflections).1H NMR and13C NMR data for the above-mentioned compounds and a third model, the diacetate of 5,5-bis(1-hydroxyethyl)-2,2,3,3-tetramethoxybiphenyl, are reported. Observed signal positions are compared with those calculated on the basis of crystal structure data. The possibilities to obtain structural information about biphenyl structures in lignins from NMR spectra are discussed. 相似文献
2.
2-(3,4-Dimethoxyphenyl)-5,6-dimethoxy-1H-indene (obtained by acid treatment of 1,2-bis(3,4-dimethoxyphenyl)-1,3-propanediol) crystallizes in space groupP21/c witha=6.836(6),b=28.631(9),c=16.344(6) Å, =95.73(5)°, andZ=8. There are two molecules in the asymmetric unit; the conformations of these molecules exhibit minor differences. In the crystals the double bond in the five-membered ring of the compound is disordered over two positions. The nature of the bonds in the five-membered ring could be ensured by1H-NMR and13C-NMR spectral examinations. 相似文献
3.
R. K. Murmann Rainer Glaser Charles L. Barnes 《Journal of chemical crystallography》2005,35(4):317-325
The X-ray structures of solid nitroguanidine (ngoH):orthorhombic, Fdd2, a = 17.6181(14), b = 24.848(2), c = 3.5901(4) Å, V = 1571.7(3) Å3, Z = 16 and nitrosoguanidine (ngH); monoclinic, P 21/n, a = 3.64510(10), b = 11.746(2), c = 8.6483(14) Å, = 99.167(2), V = 365.55(9) Å3, Z = 4 have been determined utilizing single crystal X-ray diffraction methods. The results are compared with the most stable gaseous configurations derived from ab inito calculations. The lowest energy calculated configuration for the ligands and experimentally observed crystal structures are in excellent agreement. In the solid state, both the ngoH and ngH contain discrete molecules in their unit cells which are planar (within experimental error), in the diamine configurations and are structurally identical except for an oxygen atom. In solid ngH, two ligand molecules have four nitrogen atoms arranged in a plane such that they are suitable for coordination to a nickel ion (1.945, 2.064 Å), when it is at the 1/2, 1/2, 1/2 unit-cell position giving the observed complex. As far as we are aware, this is the first instance in which a ligand crystal structure is essentially the same, with minor distance, angle and torsion angle changes, as the complex it forms and suggests some potentially unique properties and applications for this material. 相似文献
4.
Rajnikant V.K. Gupta E.H. Khan S. Shafi Shafiullah Dinesh 《Journal of chemical crystallography》2002,32(9):325-329
Cholest-3,5-diene-7-one-oxime (C27H43NO) was prepared using a usual synthetic route and its three-dimensional structure was determined by X-ray diffraction methods. The transparent platelike crystals of this compound crystallized in the monoclinic space group P21, with unit cell parameters a = 14.302(2) Å, b = 11.475(2) Å, c = 15.919(4) Å, = 106.04(1)°, (Cu K) = 1.5418 Å, Z = 4. The structure was solved by direct methods and refined to an R-value of 0.075 for 4640 observed reflections. Two crystallographically independent molecules were observed in the asymmetric unit cell. The ring A in both the molecules was found to exist in 1,10
half-chair conformation while ring C in chair conformation. The rings B and D in both the molecules adopted different conformations. Three intermolecular interactions of the type C–H O and C–H N were also observed. 相似文献
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6.
Rajnikant Lovely Sarmal Kamni Dinesh M. B. Deshmukh 《Journal of chemical crystallography》2009,39(11):835-837
Abstract
The title compound belongs to acylal class of organic materials and it crystallizes in the monoclinic space group P21/c with unit cell parameters a = 7.643(2) ?, b = 20.546(6) ?, c = 7.783 ?, β = 112.206(2)°, V = 1131.50(5) ?3 and Z = 4. The structure has been solved by direct methods and the final R-factor is 0.0401 for 2579 unique reflections. The acetate groups are deviated significantly from the plane of phenyl ring atoms. There are two C–H···O intermolecular hydrogen bonds which gives rise to an antiparallel dimer pattern. 相似文献7.
P. P. Haasbroek D. W. Oliver A. J. M. Carpy 《Journal of chemical crystallography》1998,28(11):811-814
The azlactone of 6-chloroveratraldehyde 3 (4-(2-chloro-4,5-dimethoxybenzylidene)-2-methyl-5-oxazolone) was synthesized from 6-chloroveratraldehyde 2 and its structure investigated using X-ray crystallographic and nuclear magnetic resonance methods. Compound 3 crystallized in the P21/c (#14) space group (Z = 4) with cell dimensions a = 9.148(2), b = 22.938(2), c = 6.707(1) Å, and = 111.50(2)°. The X-ray study shows that azlactone 3 exists as the Z-isomer and crystallizes as a planar structure, i.e., both the phenyl and azlactone ring systems, as well as the functional groups attached to them, lie in the same plane. The 1H and 13C NMR spectral values also support the formation of the Z-isomer only, during the synthesis of 4-(2-chloro-4,5-dimethoxybenzylidene)-2-methyl-5-oxazolone. 相似文献
8.
Michel Bardet Marie Françoise Foray Shiming Li Knut Lundquist Rolf Stomberg 《Journal of chemical crystallography》1999,29(9):1023-1029
trans-1,3-Bis(3,4-dimethoxyphenyl)-2,3-epoxy-1-propanone crystallizes in a monoclinic form (m.p. 155–156°C, from ethanol) and a trigonal form (m.p. 125–126°C, from chloroform/hexane or chloroform). NMR studies revealed that chloroform is present in the crystals of the trigonal form (epoxide/chloroform ratio 3:1). Solid-state NMR experiments showed that the trigonal form was gradually converted into the monoclinic form on storage in vacuo. On the basis of NMR and X-ray examinations it was concluded that the trigonal form is an inclusion compound of trans-1,3-bis(3,4-dimethoxyphenyl)-2,3-epoxy-1-propanone with chloroform. The crystal structure of the trigonal form with space group of R
, a = 36.0354(4), c = 8.2743(2) Å, and Z = 18, has been refined to R = 0.0506 by the employment of the SQUEEZE procedure implemented in PLATON-94. 相似文献
9.
Andrzej Maślankiewicz Mirosław Wyszomirski Tadeusz Głowiak Adolf Gogoll 《Journal of chemical crystallography》1991,21(5):559-565
The title compound (C11H11NS2) is monoclinic:P21/c,a=15.200(4),b=14.644(4),c=10.098(3),Z=8. The structure was solved by direct methods, and refined to anR value of 0.047 with 2886 independent reflections. There are two nonequivalent molecules in the unit cell. BothS-methyl groups have different spatial orientation: the-methyl group side-chain is approximately coplanar with the pyridine ring and turned to the ortho-position, but -methyl group side-chain is turned over this ring. Both1H and13C NMR spectra were assigned using 1D and 2D experiments. The NOE measurements are consistent with inter-proton distances from X-ray data.Part XV in the series of Azinyl sulfides. 相似文献
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Th. E. Weirich 《Crystallography Reports》2004,49(3):379-389
The metal-rich compound Zr2Se is of particular interest for electron crystallography, since it was one of the first examples that proved that heavy-atom structures can be solved via quasi-automatic direct methods from selected area electron diffraction intensities [1]. For this reason, Zr2Se has been chosen as a model to discuss the possibilities and the limits of the quasi-kinematical approach that has been successfully used to determine this and related structures from high-resolution electron microscopy (HREM) images and selected area electron diffraction. In order to quantify the achievable accuracy of the electron crystallography techniques used, the corresponding structures are compared with results from structural analysis with X-ray powder data and with a model received from first-principles calculations. The latter structure was chosen in this study as a reference, since the calculations do not depend on experimental parameters. Analysis of the obtained result from electron diffraction structural analysis (EDSA) shows that the structural model is, on average, only off by 0.08 Å, despite the investigated crystal having an effective thickness of 286 Å. The corresponding result from Rietveld refinement with X-ray powder data agrees to within 0.04 Å with the structure from calculation and within 0.03 Å with the result from an earlier single crystal X-ray study [2]. 相似文献
12.
V. V. Balaev A. A. Lashkov I. I. Prokofev A. G. Gabdulkhakov T. A. Seregina A. S. Mironov C. Betzel A. M. Mikhailov 《Crystallography Reports》2016,61(5):830-841
Pyrimidine nucleoside phosphorylases, which are widely used in the biotechnological production of nucleosides, have different substrate specificity for pyrimidine nucleosides. An interesting feature of these enzymes is that the three-dimensional structure of thymidine-specific nucleoside phosphorylase is similar to the structure of nonspecific pyrimidine nucleoside phosphorylase. The three-dimensional structures of thymidine phosphorylase from Salmonella typhimurium and nonspecific pyrimidine nucleoside phosphorylase from Bacillus subtilis in complexes with a sulfate anion were determined for the first time by X-ray crystallography. An analysis of the structural differences between these enzymes demonstrated that Lys108, which is involved in the phosphate binding in pyrimidine nucleoside phosphorylase, corresponds to Met111 in thymidine phosphorylases. This difference results in a decrease in the charge on one of the hydroxyl oxygens of the phosphate anion in thymidine phosphorylase and facilitates the catalysis through SN2 nucleophilic substitution. Based on the results of X-ray crystallography, the virtual screening was performed for identifying a potent inhibitor (anticancer agent) of nonspecific pyrimidine nucleoside phosphorylase, which does not bind to thymidine phosphorylase. The molecular dynamics simulation revealed the stable binding of the discovered compound—2-pyrimidin-2-yl-1H-imidazole-4-carboxylic acid—to the active site of pyrimidine nucleoside phosphorylase. 相似文献
13.
I. S. Vinogradova 《Crystallography Reports》2001,46(2):288-291
This work is a part of the systematic study of the structure and the physical properties of alkaline hydroselenite crystals with the general formula MeHSeO3, where Me is an alkali ion. The characteristic feature of this family is a net of hydrogen bonds between SeO3 groups forming closed [HSeO 3 ? ]2 dimers. 相似文献
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15.
X-ray diffraction studies of phase transitions in (NH4)2SbF3 single crystals have been made by using the Bond-type diffractometer for high-precision measurements of the unit-cell dimensions in a function of temperature. The principal linear thermal expansion coefficients and the linear Eulerian strain tensor have been calculated in the temperature interval 110 – 298 K. The phase transition diagram was proposed and the sequence of the phases has been compared with the results of other experimental techniques (NMR, NQR, DTA, electrophysical methods). 相似文献
16.
S. Arumugam S. V. Bhat N. Kumar K. V. Ramanathan R. Srinivasan 《Molecular Crystals and Liquid Crystals》2013,570(2-4):161-173
Abstract Wideline and high resolution NMR studies have been carried out on MBBA in its isotropic, nematic and solid phases. Isotropic and nematic phase spectra correspond to what has been reported earlier. In the solid phase, contrary to expectations, very intense narrow signals similar to signals of the isotropic phase have been observed for the first time at temperatures close to the solid ? nematic phase transition temperature. This indicates rapid reorientational or translational motion in the system. The X-ray results however confirm the existence of translational order. The results are interpreted as indicative of the existence of a plastic crystalline phase in MBBA. 相似文献
17.
Adriano Benedetti Antonio C. Fabretti Carlo Preti 《Journal of chemical crystallography》1988,18(6):685-692
The compound C14H24HgN2S4 was prepared and characterized by means of X-ray, IR, and NMR measurements. The crystals are monoclinic, space group P21/c, (No. 14) witha=8.697(2),b=19.156(3),c=12.098(2) Å,=108.14(1)° andZ=4. The structure was solved by the heavy-atom method, and least-squares refinement of structural parameters led to a conventionalR factor of 0.027 for 2469 independent reflections. The structure consists of discrete dimeric units with the metals coordinated to five sulphur atoms. The IR and NMR spectra are discussed on the basis of the known structure. 相似文献
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19.
The crystal structure of 2,4-dinitrophenyl phenylsulfide, C12H8N2O4S, has been determined by single crystal X-ray diffraction. The crystals are monoclinic, space groupP2
1/n, Z = 8, witha = 10.670(2),b = 8.381(4),c = 27.998(18) Å, and = 100.44(4) °. There are two crystallographically independent molecules per asymmetric unit. All intensity measurements were made at room temperature on an Enraf-Nonius CAD-4 automatic diffractometer using monochromatized MoK radiation. The structure was solved by direct methods and refined to a finalR value of 0.032. The two independent molecules have nearly identical geometries, with the most notable difference being the torsion angles involving the sulfur atoms. Thepara-nitro groups are more nearly in the planes of the central phenyl rings than are theortho-nitro groups although there may be nonbonded attractions between the latter. The two phenyls of each molecule are nearly at right angles to each other, as necessitated by steric forces involvingortho hydrogens. The characteristic distortions of the central phenyl rings caused by differing substituent electronegativities and degrees of conjugation are noted. The13C-NMR spectrum of the compound was assigned by comparison of calculated with observed chemical shift data. Calculated chemical shifts were obtained by incrementation of the chemical shifts of diphenylsulfide with standard nitro group additivities which were adjusted for the sulfur-nitro group interaction. Where necessary, assignments were confirmed with selective excitation spin-coupled subspectra. Solution behavior of the molecule was determined from spin-lattice (T
1) relaxation measurements which showed the unsubstituted ring to reorient anisotropically about the C(21)-C(24) bond axis while the substituted ring appears to be governed by the overall isotropic reorientation of the molecular framework, indicating that the sulfur-nitro group interaction restricts anisotropic reorientation about the C(11)-C(14) bond axis. 相似文献
20.
《Journal of Non》2005,351(8-9):632-639
Neutron and X-ray scattering studies of (Li2O)x–(TeO2)2–V2O5 glasses with x = 0, 1 and 2, obtained by melting and subsequent cooling in air to room temperature, have been performed. Reciprocal space data have been Fourier transformed into real space yielding the radial distribution functions. Nearest and next neighbor peaks have been analyzed using a least-squares fitting method which suggests the presence of both TeO3 and TeO4 coordination polyhedra, the fivefold coordination of lithium and mixture of 6, 5 and 4 coordination numbers of vanadium. These results are discussed in relation to the electronic and ionic conductivity properties. 相似文献