Structural parameters for the chair or twist-boat conformations of 1,3-dioxa-5,6-benzocycloheptene and its 2-methyl and 2,2-dimethyl derivatives

1986 ◽  
Vol 64 (3) ◽  
pp. 500-506 ◽  
Author(s):  
Robert St-Amour ◽  
Marc J. Olivier ◽  
Maurice St-Jacques ◽  
François Brisse
Keyword(s):  
Low Temperature ◽  
Oxygen Atom ◽  
Structural Parameters ◽  
Lone Pair ◽  
Molecular Conformations ◽  
X Ray ◽  
Bond Lengths ◽  
Structural Differences ◽  
Back Donation ◽  
Twist Boat

Low temperature X-ray studies of 1,3-dioxa-5,6-benzocycloheptene (1) and its 2-methyl (2) and 2,2-dimethyl derivatives (3) show that 1 and 2 exist in the crystal state exclusively in the chair (C) form while 3 exists exclusively in the twist-boat (TB) form. The final values of the agreement index, Rw, are 0.048, 0.059, and 0.046 for 1, 2, and 3, respectively. Significant structural differences between the g+g+ arrangement of the acetal moiety with the TB form and the g+g− disposition in the C form are revealed. These differences can be interpreted as arising from a less efficient back-donation of an antiperiplanar lone pair on the oxygen atom in the g+g+ relative to the g+g− arrangement. Furthermore, the C—O bond lengths shed some light on the hybridization state of the lone pairs of electrons on oxygen. Finally the results are used to rationalize nmr observations in terms of molecular conformations in solution.

The Through-Bond Interaction of a Sulfur Lone Pair with Oxygenated Substituents in the Thiacyclohexane Framework

2005 ◽  
Vol 58 (7) ◽  
pp. 531
Author(s):  
Laura Andrau ◽  
Jonathan M. White
Keyword(s):  
Low Temperature ◽  
Crystal Structures ◽  
Bond Distance ◽  
Lone Pair ◽  
X Ray ◽  
Ester Derivative ◽  
Bond Interaction ◽  
Derivatives Of ◽  
Electron Demand

Low-temperature X-ray crystal structures were determined on a range of derivatives of 4-thiacyclohexanol 5a of varying electron demand with a view to finding evidence for a through-bond interaction between the sulfur lone pair and the oxygenated substituent. In contrast to earlier suggestions, plots of C–OR bond distance versus pKa (ROH) showed that any interaction between the sulfur and the OR group is unlikely to be of a through-bond origin. Furthermore, unimolecular solvolysis rate measurements on the nosylate ester derivative 5g showed that the sulfur actually retards the reaction slightly in comparison with the corresponding sulfur-free analogue 6.

Structure of russellite (Bi2WO6): origin of ferroelectricity and the effect of the stereoactive lone electron pair on the structure

2018 ◽  
Vol 74 (3) ◽  
pp. 295-303 ◽  
Author(s):  
Hiroki Okudera ◽  
Yuka Sakai ◽  
Kentaro Yamagata ◽  
Hiroaki Takeda
Keyword(s):  
Low Temperature ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Lone Pair ◽  
Orthorhombic Phase ◽  
Electrostatic Charge ◽  
X Ray Diffraction ◽  
Coordination Environment ◽  
X Ray ◽  
Powder Neutron Diffraction

The structure of the low-temperature polar (orthorhombic) phase of russellite (Bi2WO6) was examined on artificial specimens with precise single-crystal X-ray diffraction experiments. The final atomic arrangement thus obtained was identical to that reported by Knight [Miner. Mag. (1992), 56, 399–409] with powder neutron diffraction. The residual density attributable to a stereochemically-active lone pair of electrons of bismuth was prominent at approximately the centre of a larger cap of BiO8 square antiprisms, that is on the line from the Bi sites to an adjacent WO4 2− slab along the b-axis direction. Quite uneven Bi—O distances and the formation of a vacant coordination hemisphere (within 3 Å) should, therefore, be ascribed to the strong demand of bismuth to form shorter Bi—O bonds to use up its electrostatic charge within its coordination environment. The shift of bismuth along −c propagates via the correlated shift of the W site and these cooperative shifts cause ferroelectricity in the compound. This propagation was easily effected by the intrusion of molecules such as acetone into the structure.

Influence of Trimethylsilyl Substituents on Primary C - O Bond Lengths at the b-Position: Results from Low-Temperature X-Ray Structural Studies

1997 ◽  
Vol 50 (9) ◽  
pp. 927 ◽  
Author(s):  
Alison J. Green ◽  
William Issa ◽  
Jonathan M. White
Keyword(s):  
Low Temperature ◽  
Ester Bond ◽  
Structural Studies ◽  
Structural Effects ◽  
X Ray ◽  
Bond Lengths

The β-trimethylsilyl substituent in 2-trimethylsilylethyl p-nitrobenzoate (12b) and 2-trimethylsilylethyl 2,4-dinitrobenzenesulfenate (12c) leads to significant lengthening of the C(alkyl)–O(ester) bond. Lengthening of the Si-CH2 distance in the more electronegative ester (12c) relative to (12b) is also observed. These structural effects are consistent with the presence of σC-Si–σ* C-O interactions.

scholarly journals Catalytic activity of nanostructured Au: Scale effects versus bimetallic/bifunctional effects in low-temperature CO oxidation on nanoporous Au

2013 ◽  
Vol 4 ◽  
pp. 111-128 ◽  
Author(s):  
Lu-Cun Wang ◽  
Yi Zhong ◽  
Haijun Jin ◽  
Daniel Widmann ◽  
Jörg Weissmüller ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Low Temperature ◽  
Co Oxidation ◽  
Surface Area ◽  
Photoelectron Spectroscopy ◽  
Scale Effects ◽  
Structural Parameters ◽  
Kinetic Measurements ◽  
X Ray ◽  
Low Temperature Co Oxidation

The catalytic properties of nanostructured Au and their physical origin were investigated by using the low-temperature CO oxidation as a test reaction. In order to distinguish between structural effects (structure–activity correlations) and bimetallic/bifunctional effects, unsupported nanoporous gold (NPG) samples prepared from different Au alloys (AuAg, AuCu) by selective leaching of a less noble metal (Ag, Cu) were employed, whose structure (surface area, ligament size) as well as their residual amount of the second metal were systematically varied by applying different potentials for dealloying. The structural and chemical properties before and after 1000 min reaction were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic behavior was evaluated by kinetic measurements in a conventional microreactor and by dynamic measurements in a temporal analysis of products (TAP) reactor. The data reveal a clear influence of the surface contents of residual Ag and Cu species on both O2 activation and catalytic activity, while correlations between activity and structural parameters such as surface area or ligament/crystallite size are less evident. Consequences for the mechanistic understanding and the role of the nanostructure in these NPG catalysts are discussed.

Improved Synthetic Route to Unsymmetrically Substituted Phosphinimino-phosphonium Salts. Crystal Structure of Tri-n-butyl- [tris(diethylamino)phosphinimino]phosphonium Chloride

2001 ◽  
Vol 56 (12) ◽  
pp. 1319-1321 ◽  
Author(s):  
R. Bartsch ◽  
M. Freytag ◽  
S. Goller ◽  
R G. Jones ◽  
R. Schmutzler
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Title Compound ◽  
Phosphonium Salts ◽  
Synthetic Route ◽  
X Ray ◽  
Bond Lengths ◽  
Phosphonium Chloride

Abstract The title compound was prepared from tri-n-butyl-chlorophosphonium chloride and N-tri-methylsilyl-tris(diethylamino)-phosphinimine. A low temperature X-ray crystal structure de­termination revealed PN bond lengths of 156.1(2) and 158.0(2) pm, with a PNP angle of 149.36(17)°.

A contribution to the structure of coals from x-ray diffraction studies

1960 ◽  
Vol 252 (1019) ◽  
pp. 557-602 ◽  
Keyword(s):  
Bond Length ◽  
Structural Model ◽  
Structural Parameters ◽  
Amorphous Material ◽  
Average Bond Length ◽  
Size Distributions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structural Differences ◽  
Average Bond

Detailed X-ray diffraction studies have been carried out on a series of vitrains, anthracites, lignites, durains, fusains and certain coal extracts, of varying rank. The results are interpreted in terms of a basic structural model in which the carbon atoms are arranged in small aromatic layers linked to each other by aliphatic or alicyclic material or by five-membered rings to form large buckled sheets. Data have been obtained on the layer size distributions, the average layer diameters, the average bond length, the proportion of amorphous material and on the nature of the packing. The significance of the various structural parameters deduced from X-ray data is discussed critically. All the results are considered together in an attempt to develop as detailed a structural model as possible. The nature of the coalification process and the structural differences between various macerals are discussed and the results are compared with those deduced from other studies.

Strukturverfeinerung von Kalium - periodat bei 297 und 150 K/Structure Refinement of Potassium Periodate at 297 and 150 K

1996 ◽  
Vol 51 (3) ◽  
pp. 444-446 ◽  
Author(s):  
Danita de Waal ◽  
Klaus-Jürgen Range
Keyword(s):  
Low Temperature ◽  
Single Crystal ◽  
Structural Parameters ◽  
Structure Refinement ◽  
Potassium Periodate ◽  
Space Group ◽  
X Ray ◽  
Two Temperatures

Abstract The scheelitetype structure of potassium perio­date, KIO4, has been confirmed and refined from single-crystal X-ray data at two temperatures. The compound crystallizes tetragonally, space group I41/a, with a = 5.726(1), c = 12.607(4) Å at 297(1) K, and a = 5.704(3), c = 12.478(8) Å at 150(1) K, respectively. Except for a significant decrease in the anisotropic displacement factors, the changes in the structural parameters at low temperature are rather small.

Notizen: Synthesis and Crystal Structure of the Hydrogen Bonded Complex of Tri-paratoluidylphosphazenyl Oxide with Ethyl Alcohol

1976 ◽  
Vol 31 (9) ◽  
pp. 1295-1296 ◽  
Author(s):  
T. Stanley Cameron ◽  
M. Gerard Magee ◽  
Samuel Mclean
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bond ◽  
Oxygen Atom ◽  
Ethyl Alcohol ◽  
Title Compound ◽  
Synthesis And Crystal Structure ◽  
X Ray ◽  
Bond Lengths ◽  
X Ray Crystallography ◽  
Phosphoryl Oxygen

The title compound was synthesised and its structure determined by X-ray crystallography. The structure contains a hydrogen bond between the OH group of the alcohol and the phosphoryl oxygen atom. The P–N bond lengths are significantly different and the differences can be attributed to varying ρπ—dπ interactions along the bonds.

Low-temperature X-ray diffraction studies on [Cu(4-Xpz)2]x linear chain polymers (where X = Cl, Br, CH3, H; pz = pyrazolate)

1993 ◽  
Vol 71 (3) ◽  
pp. 331-334 ◽  
Author(s):  
Martin K. Ehlert ◽  
Alan Storr ◽  
Robert C. Thompson ◽  
Frederick W. B. Einstein ◽  
Raymond J. Batchelor
Keyword(s):  
Low Temperature ◽  
Room Temperature ◽  
Copper Ions ◽  
Structural Parameters ◽  
Linear Chain ◽  
Crystallographic Axis ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
X Ray ◽  
Cell Parameters

Room temperature and low-temperature (110–140 K) powder diffractograms have been obtained for the polymeric compounds [Cu(4-Xpz)2]x (where X = H, CH3, Cl, and Br), and values of the unit cell parameters (orthorhombic, space group Ibam) a, b, and c have been obtained at both high and low temperatures. A single crystal X-ray diffraction study of the X = H compound at 116 K was completed and the results compared with a published study done at room temperature. The structures of these complexes involve extended chains of pyrazolate-bridged copper ions extending along the c crystallographic axis. The X-ray studies indicate little change in the c parameter with decreasing temperature and small but significant changes in the a or b parameters reflecting changes in interchain packing. This study permits some evaluation of how structural parameters are affected by these variations in interchain packing and how these variations may be affecting the magnitude of magnetic exchange in the compounds.

Pump and probe X-ray absorption fine structure using high-brilliance photon sources

1998 ◽  
Vol 5 (3) ◽  
pp. 1001-1003 ◽  
Author(s):  
H. Oyanagi ◽  
A. Kolobov ◽  
K. Tanaka
Keyword(s):  
Fine Structure ◽  
Low Temperature ◽  
Optical Pumping ◽  
Lone Pair ◽  
Amorphous Selenium ◽  
Fluorescence Excitation ◽  
X Ray ◽  
Absorption Fine ◽  
Pump And Probe ◽  
X Ray Absorption

Pump and probe X-ray absorption fine structure (XAFS) is used as a local probe of excited atoms, which can provide direct information on lattice distortion, relaxation and atomic rearrangements associated with electronic excitations. In situ XAFS experiments during optical excitation are reported. Utilizing a grazing-incidence fluorescence excitation, which minimizes the mismatch between the probing depths of X-ray excitation and optical pumping, it is found that the dominant photoinduced defect state in amorphous selenium at low temperature is a pair of threefold neutral C^0_3 states: 2C^*_2 \rightarrow (C^0_3-C^0_3), where C^*_2 denotes the twofold excited lone-pair state. The results indicate that optical pumping of chalcogen atoms at low temperature leads to locally over-coordinated defect pairs similar to those in the liquid state. The origin of reversible photostructural changes, such as photodarkening or photoinduced fluidity, is attributed to the structural disorder caused by the formation and annihilation of dynamical interchain bonds during optical melting.

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