Heterocyclic Compounds from Alloxan and Amines. XIV. Structure of Even-Electron Products Derived from Free-Radical Betaines

1979 ◽  
Vol 32 (9) ◽  
pp. 1943 ◽  
Author(s):  
JW Clark-Lewis ◽  
MR Taylor ◽  
J Westphalen
Keyword(s):  
Free Radical ◽  
Least Squares ◽  
Heterocyclic Compounds ◽  
Full Matrix ◽  
X Ray ◽  
Dimer Structure

X-ray crystallographic determination of structure has shown that the even-electron product obtained thermally from 5-(10-phenyl-5,10-dihydro-5-phenazinioyl)-1,3-dimethyl-4-barbiturate (1) (e.g. by heating in benzene) has the structure 1,3-dimethy1-5-(10-phenyl-2,10-dihydrophenazin-2-ylidene)- hexahydropyrimidine-2,4,6-trione (3) instead of the previously supposed dehydro dimer structure (2). Crystals of compound (3) are triclinic, Pī, a 11�014(3), b 9�343(3), c 10�927(3) �, α 110�47(4), β 64�99(4), γ 101�47(4)�, Z = 2. Full-matrix least-squares refinement gave R 0�09. The rearrangement that occurs in the conversion of the free-radical betaine (1) into the trione (3) is a novel type of N to p-aromatic rearrangement which presumably entails dissociation followed by recombination and oxidation.

1,2,3,4-Tetra-O-acetyl-β-D-arabinopyranose: A Neutron Refinement and Comparison with X-Ray Refinement

2002 ◽  
Vol 55 (2) ◽  
pp. 167 ◽  
Author(s):  
V. J. James ◽  
F. H. Moore ◽  
J. D. Stevens
Keyword(s):  
Neutron Diffraction ◽  
Least Squares ◽  
Diffraction Study ◽  
Neutron Diffraction Study ◽  
Precise Determination ◽  
Hydrogen Atoms ◽  
Full Matrix ◽  
X Ray ◽  
Motion Parameters

A neutron diffraction study of 1,2,3,4-tetra-O-acetyl-β-D-arabinopyranose, C13H18O9, has been carried out. Space group P21; Z 2; a 10.0779(5), b 9.0228(5), c 8.9659(5) �and β 101.965(5)°. Full-matrix least squares refinements varying anisotropic parameters for all atoms have led to a discrepancy value over all data of 0.058 and R w 0.054. This structure gives a precise determination of position and thermal motion parameters for all hydrogen atoms. The neutron diffraction results agree well with the X-ray results for non-hydrogen positional and thermal parameters.

Structural Chemistry of the Platinum Group-Metals: MCl2(bpy) (M = Pd, Pt, bpy = 2,2′-Bipyridine)

1992 ◽  
Vol 45 (2) ◽  
pp. 417 ◽  
Author(s):  
AJ Canty ◽  
BW Skelton ◽  
PR Traill ◽  
AH White
Keyword(s):  
Least Squares ◽  
Structure Determination ◽  
Structural Chemistry ◽  
Platinum Group Metals ◽  
Full Matrix ◽  
X Ray ◽  
Planar Molecules ◽  
Platinum Group

A singlecrystal X-ray structure determination of (2,2′-bipyridine)dichloropalladium(II), iso- morphous with the 'yellow' form of the platinum(II) analogue, has been carried out. Crystals are orthorhombic, Pbca, a 18.144(5), b 15.952(5), c 7.494(2) A, Z 8, 1113 diffractometer reflections being refined by full matrix least squares to a residual of 0.052. The planar molecules of PdCl2(bpy) are stacked into columns along the c direction, at a separation of c/2, neighbouring molecules in the stacks being related by glide planes with Pd…Pd separations of 4.587(2) A.

Diiodo Acetals and Unsaturated Lactones From Dihydropyran

1993 ◽  
Vol 46 (2) ◽  
pp. 203 ◽  
Author(s):  
MJ Lynch ◽  
J Simpson ◽  
RT Weavers
Keyword(s):  
Free Radical ◽  
X Ray ◽  
Ester Formation ◽  
Propiolic Acid ◽  
Unsaturated Lactones ◽  
By Products

Reaction of dihydropyran with propiolic acid and N- iodosuccinimide gave an iodo ester which was cyclized under free-radical conditions to form an (E) iodomethylene lactone. Photolysis of this lactone could be controlled to generate mixtures of (E) and (Z) iodomethylene lactones, or alternatively the iodine-free methylene lactone. The structures of some by-products of the iodo ester formation have been shown to be a succinimide derivative and two stereoisomers of a diiodo acetal. X-Ray determination of the structure of one of the diiodo acetal isomers is described.

Crystal structure of Tetracyclo[5,3,1,12,6,04,9]dodecane (iceane)

1977 ◽  
Vol 30 (8) ◽  
pp. 1837 ◽  
Author(s):  
DPG Hamon ◽  
CL Raston ◽  
GF Taylor ◽  
JN Varghese ◽  
AH White
Keyword(s):  
Crystal Structure ◽  
Rigid Body ◽  
Least Squares ◽  
Title Compound ◽  
Molecular Geometry ◽  
Thermal Motion ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
X Ray ◽  
Hexagonal Close Packed

The crystal structure of the title compound, C12H18, has been determined at 295 K by X-ray diffraction and refined by full-matrix least squares to a residual of 0.049 for 216 ?observed? reflections; molecular geometry has been corrected for the effects of thermal motion using a rigid body approximation. Crystals are hexagonal, P63/m, a = 6.582(1), c = 11.843(3) Ǻ, Z = 2, the molecules occupying a hexagonal close- packed array.

Synthesis and Structure of cis-Dioxobis(pyrimidine-2-thiolato-N,S)molybdenum(VI)

1992 ◽  
Vol 45 (11) ◽  
pp. 1933 ◽  
Author(s):  
PR Traill ◽  
AG Wedd ◽  
ERT Tiekink
Keyword(s):  
Least Squares ◽  
Octahedral Geometry ◽  
Distorted Octahedral Geometry ◽  
Monoclinic Space Group ◽  
Full Matrix ◽  
X Ray ◽  
Distorted Octahedral ◽  
Cell Dimensions ◽  
Unit Cell Dimensions

The characterization of two MoVI complexes, cis -[MoO2(2-pymS)2] and cis -[MoO2(2-pyS)2] (where 2-pymSH is pyrimidine-2-thiol and 2-pySH is pyridine-2-thiol), and their reaction with Ph3P are reported. The X-ray structure of cis -[MoO2(2-pymS)2] shows the molybdenum atom to exist in a distorted octahedral geometry defined by two mutually cis oxygen atoms and two chelating 2-pymS ligands so that the two sulfur atoms occupy approximate trans positions. Crystals of cis -[MoO2(2-pymS)2] are monoclinic, space group P 21/n, with unit cell dimensions: a 9.301(3), b 12.121(2), c 11.303(3) �, β 112.62(3)�, V 1176.3 �3, Z 4. The structure was refined by a full-matrix least-squares procedure to R 0.067 for 1858 reflections with I ≥ 2.5 (I).

A REFINEMENT OF THE CRYSTAL STRUCTURES OF (NH4)2TeBr6 AND Cs2TeBr6

1966 ◽  
Vol 44 (8) ◽  
pp. 939-943 ◽  
Author(s):  
A. K. Das ◽  
I. D. Brown
Keyword(s):  
Least Squares ◽  
Crystal Structures ◽  
Diffraction Data ◽  
Bromine Atom ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
X Ray ◽  
Anisotropic Temperature ◽  
Temperature Factors

(NH4)2TeBr6 and Cs2TeBr6 crystals have the cubic K2PtCl6 structure with space group: [Formula: see text] with a0 = 10.728 ± 0.003 Å and 10.918 ± 0.002 Å respectively. The positional coordinate of the bromine atom, and the anisotropic temperature factors of all atoms in the unit cell, have been refined for both crystals by a full matrix least-squares analysis of the three dimensional X-ray diffraction data (R = 0.08). The Te—Br distance, corrected for probable thermal motions of atoms forming the bond, is 2.70 ± 0.01 Å in both crystals.

Crystal and molecular structure of 3-ethyl-4-hydroxy-1,2,3(4H)-benzotriazine and 6-chloro-4-hydroxy-3-methyl-4-phenyl-1,2,3-benzotriazine

1985 ◽  
Vol 63 (3) ◽  
pp. 581-585 ◽  
Author(s):  
Kwong Khee Lai ◽  
Carl H. Schwalbe ◽  
Keith Vaughan ◽  
Ronald J. Lafrance ◽  
Clive D. Whiston
Keyword(s):  
Molecular Structure ◽  
Hydrogen Bonds ◽  
Least Squares ◽  
Least Squares Method ◽  
Crystal And Molecular Structure ◽  
Tetrahedral Geometry ◽  
Orthorhombic System ◽  
Full Matrix ◽  
X Ray ◽  
R Factor

The crystal structures of the title compounds have been determined from X-ray data collected on a four-circle diffractometer and refined by the full-matrix least-squares method. The former compound crystallizes in the orthorhombic system, space group Pbcn, with a = 14.346(8), b = 7.239(1), c = 17.276(2) Å, and has been refined to a conventional R factor of 0.043 for 890 observed reflections. Corresponding results for the latter compound are monoclinic, P21/n, a = 12.222(4), b = 7.482(2), c = 14.170(8) Å, β = 94.06(4)°, R = 0.060 for 2128 observed data. The triazine rings of both compounds exhibit short N(1)—N(2) bonds and tetrahedral geometry at C(4); however, the ring is puckered in the first compound but flat in the second. Molecules in both crystals are linked by [Formula: see text] hydrogen bonds.

Crystal Structure of N,N,N′,N′-Tetrakis-(trimethylsilyl)ethane-1,2-diamine

1985 ◽  
Vol 38 (11) ◽  
pp. 1729 ◽  
Author(s):  
LM Engelhardt ◽  
CL Raston ◽  
AH White
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Least Squares ◽  
Structure Determination ◽  
Title Compound ◽  
Full Matrix ◽  
X Ray ◽  
Methylene Groups

The title compound, [{(Me3Si)2NCH2}2], has been structurally characterized by a single-crystal X-ray structure determination at 130 K, being refined by full-matrix least-squares to a residual of 0.057 for 1244 'observed' reflections. Crystals are monoclinic, C2/c, a 21.00(2), b 9.089(8), c 11.744(9) Ǻ, β 92.31(7)°, Z 4. Molecules lie on inversion centres, but with some disorder of the methylene groups. Si -N are 1.735 Ǻ, and N-CH2 1.53(1) for the major fragment (70%). The nitrogen in the major fragment is approximately trigonal planar; Si -N- Si 124.6(3)°, Si -N-C 117.5(4), 115.5(4)°.

The Flavonoids of Combretum quadrangulare: Crystal structures of the Polymorphic Forms of 5-Hydroxy-2-(4'-hydroxy-3',5'-dimethoxyphenyl)-3,7-dimethoxy-4H-1-benzopyran-4-one

1985 ◽  
Vol 38 (8) ◽  
pp. 1177 ◽  
Author(s):  
IR Castleden ◽  
SR Hall ◽  
S Nimgirawath ◽  
S Thadaniti ◽  
AH White
Keyword(s):  
Least Squares ◽  
Crystal Structures ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
X Ray ◽  
Β Phase ◽  
Α Phase ◽  
Polymorphic Forms

The following substituted 2-phenyl-4H-1-benzopyran-4-ones have been isolated from the dried flowers of Combretum quadrangulare Kurz ( Combretaceae ): 5-hydroxy-3,3′,4′,5′,7-pentamethoxy ( combretol ) (1), 3′,5-dihydroxy-3,4′,7-trimethoxy ( ayanin ) (2) and 4′,5-dihydroxy- 3,3′,5′,7-tetramethoxy (3). The last substance (3) was obtained as a mixture of two polymorphic forms (α and β) each of which was characterized by X-ray diffraction. Diffractometer data at 295 K were refined by full matrix least squares to residuals of 0.043 (1181 'observed' reflections) for the α-phase and 0.044 (1421) for the β phase of (3). Crystals of the α-phase of (3) are triclinic, Pī, a 12.663(6), b 9.592(4), c 7.444(4) Ǻ, α 102.48(3), β 101.39(4), γ 91.72(4)°,Z 2. Crystals of the β-phase of (3) are monoclinic P21/n, a 17.139(8), b 12.728(6), c 7.845(7) Ǻ, β 95.07(6)°, Z 4. An unambiguous synthesis of (3) was also achieved.

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