Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Pentafluorophenyl (3R,4R,5S)-5-{[(3R,4R,5S)-5-azidomethyl-3,4-dimethoxy-2,3,4,5-tetrahydrofuran-3-carboxamido]methyl}-3,4-dimethoxy-2,3,4,5-tetrahydrofuran-3-carboxylate  [cached]
Michela I. Simone,Alison A. Edwards,Samuel G. Parker,George E. Tranter
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810038559
Abstract: The title compound, C22H25F5N4O9, is a stable pentafluorophenyl ester intermediate in the synthesis of novel homo-oligomeric structures containing branched carbon chains. The structure is epimeric to the previously characterized dimeric pentafluorophenyl ester with stereochemistry (3R,4R,5R), which was synthesized using d-ribose as starting material. The crystal structure of the title molecule removes any ambiguities arising from the relative stereochemistries of the six chiral centres. Two hydrogen bonds, bifurcating from the NH group, stabilize the crystal: one intramolecular and one intermolecular, both involving O atoms of the methoxy groups. The asymmetric unit contains two independent molecules not related by any pseudo-symmetry operators. The major conformational differences are localized, leading to one molecule being extended compared to the other. The collected crystal was twinned (twin ratio is 0.939:0.061), and the azide group is positionally disordered over two positions in one molecule [occupancy ratio 0.511 (18):0.489 (18)].
The Minkowskian planar 4R mechanism  [PDF]
Gabor Hegedüs,Brian Moore
Mathematics , 2010,
Abstract: We characterize and classify completely the planar 4R closed chain working on the Minkowskian plane. Our work would open a new research direction in the theory of geometric designs: the classification and characterization of the geometric design of linkages working in non--Euclidean spaces.
[(3R*,4R*,5R*)-2,3-Diphenylisoxazolidine-4,5-diyl]dimethanol  [cached]
Selahaddin Guner,Kűbra Şeftalicioglu
Acta Crystallographica Section E , 2012, DOI: 10.1107/s1600536812025032
Abstract: In the title compound, C17H19NO3, the isoxazolidine ring adopts an envelope conformation with the O atom as the flap. In the crystal, O—H...O hydrogen bonds form C23(14) R22(14) motifs.
Synthesis and Physical Characterization of 4-(anthracen-10-yl)-1-cyclohexyl-3-phenoxyazetidin-2-one as a New Trans 2-azetidinone  [PDF]
Aliasghar Jarrahpour,Mohammad Nazari,Abraham F. Jalbout
Molbank , 2007, DOI: 10.3390/m538
Abstract: In this paper we propose the synthesis of 4-(anthracen-10-yl)-1-cyclohexyl-3-phenoxyazetidin-2-one. In addition to its synthesis AM1 calculations to characterize the physical properties of the molecule is also presented.
4,4′-[(2R*,3R*,4R*,5R*)-3,4-Dimethyltetrahydrofuran-2,5-diyl]diphenol  [cached]
Juan Manuel de Jesús Favela-Hernández,María del Rayo Camacho-Corona,Sylvain Bernès,Marcos Flores-Alamo
Acta Crystallographica Section E , 2012, DOI: 10.1107/s1600536812039359
Abstract: The title molecule, C18H20O3, is a furanoid lignan extracted from the leaves of Larrea tridentata. The relative absolute configuration for the four chiral centers was established, showing that this compound is 4-epi-larreatricin, which has been previously reported in the literature. The molecule displays noncrystallographic C2 symmetry, with the methyl and phenol substituents alternating above and below the mean plane of the furan ring. The conformation of this ring is described by the pseudorotation phase angle P = 171.3° and the maximum out-of-plane pucker νm = 37.7°. These parameters indicate that the furan ring adopts the same conformation as the ribose residues in B-DNA. The packing is dominated by intermolecular O—H...O hydrogen bonds. The phenol hydroxy groups form chains in the [110] direction and these chains interact via O—H...O(furan) contacts.
Topological Symmetry Groups of K_{4r+3}  [PDF]
Dwayne Chambers,Erica Flapan,John D. O'Brien
Mathematics , 2009, DOI: 10.3934/dcdss.2011.4.1401
Abstract: We present the concept of the topological symmetry group as a way to analyze the symmetries of non-rigid molecules. Then we characterize all of the groups which can occur as the topological symmetry group of an embedding of the complete graph K_{4r+3} in S^3.
(3R,4R,5R)-5-(Acetamidomethyl)-N-benzyl-3,4-dihydroxytetrahydrofuran-3-carboxamide  [cached]
Michela I. Simone,Alison A. Edwards,Andrew R. Cowley,George W. J. Fleet
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810039589
Abstract: X-ray crystallographic analysis with Cu Kα radiation established the relative configurations of the stereogenic centers in the title compound, C15H20N2O5, and clarified mechanistic ambiguities in the synthesis. The conformation of the five-membered ring approximates twisted, about a C—O bond. The absolute configuration of this carbon-branched dipeptide isostere was known based on the use of d-ribose as the starting material. Refinement of the Flack parameter gave an ambiguous result but the refined Hooft parameter is in agreement with the assumed (d-ribose) absolute structure. The crystal structure consists of N—H...O and O—H...O hydrogen-bonded bi-layers, with the terminal methyl and phenyl groups forming a hydrophobic inter-layer interface. Some weak C—H...O interactions are also present.
(3R,4R)-2,5-Dioxo-1-m-tolyl-3,4-diyl diacetate  [cached]
Sara Naz,Javid Zaidi,Tahir Mehmood,Peter G. Jones
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809020637
Abstract: In the enantiomerically pure title compound, C15H15NO6, the five-membered ring displays a twist conformation with the local axis through the N atom. The acetyl groups are perpendicular to the ring [dihedral angles 80.3 (1) and 89.3 (1)°] and project to opposite sides. The packing is governed by two weak C—H...O interactions, forming layers of molecules parallel to the ab plane.
Movilidad del Mecanismo Esférico Tipo 4R Movilidad del Mecanismo Esférico Tipo 4R
Hugo I. Medellín Castillo,J. J. Cervantes Sánchez,L. Antonio Aguilera Cortés
Acta Universitaria , 2012,
Abstract: Un mecanismo esférico se define como aquel en el que cada eslabón móvil rota respecto a un punto estacionario común, cualquier punto sobre el eslabón está restringido a moverse en una superficie esférica, y todas las superficies esféricas del movimiento son concéntricas. En este trabajo se presenta el análisis de movilidad del mecanismo esférico 4R considerando, además de la movilidad del eslabón de entrada y de salida, la movilidad del eslabón acoplador respecto al eslabón de entrada y respecto al eslabón de salida. De este análisis se derivan las condiciones de movilidad del mecanismo las cuales se presentan en diagramas de movilidad, y de este mismo análisis se obtuvieron las condiciones de movilidad global que permiten identificar de una manera sencilla, el tipo de movimiento que tendrá cada eslabón, sólo con conocer las dimensiones del mecanismo. A spherical mechanism is defined as the one in which each movable link rotates with respect to a common stationary point, any point on the link is confined to move in a spherical surface, and all spherical surfaces of the movement are concentric. In this paper the analysis of the movable spherical mechanism 4R is presented considering, besides the mobility of the link entering and exiting the mobility of the coupler link regarding the linkage entrance with regards to the linkage exit. From this analysis the conditions of mobility of the mechanism was derived and are presented in mobility diagrams and from the same analysis was obtained the conditions for global mobility that allow the identification in a simple way, the type of mobility that each link will have, with only the dimensions of the mechanism.
(2S,3R,4R,5R)-3,4-Dihydroxy-5-(hydroxymethyl)pyrrolidine-2-carboxylic acid [(2S,3R,4R,5R)-3,4-dihydroxy-5-(hydroxymethyl)proline]
Daniel Best,Sarah F. Jenkinson,Amber L. Thompson,David J. Watkin
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809035636
Abstract: The crystal structure of the title compound, C6H11NO5, establishes the relative configuration at the four stereogenic centres; the absolute configuration is determined by the use of d-glucuronolactone as the starting material for the synthesis. Molecules are linked by intermolecular O—H...O and N—H...O hydrogen bonds into a three-dimensional network, with each molecule acting as a donor and acceptor for five hydrogen bonds.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.