RESUMEN
A modern industrial route for the manufacture of methyl methacrylate involves the reaction of methyl propanoate and formaldehyde over a silica-supported Cs catalyst. Although the process has been successfully commercialised, little is known about the surface interactions responsible for the forward chemistry. This work concentrates upon the interaction of methyl propanoate over a representative silica. A combination of infrared spectroscopy, inelastic neutron scattering, DFT calculations, X-ray diffraction and temperature-programmed desorption is used to deduce how the ester interacts with the silica surface.
RESUMEN
The title compound, [Ni(C13H11N4S2)2], was obtained by the reaction of S-2-picolyldi-thio-carbazate and pyridine-2-carbaldehyde with nickel(II) acetate. The Ni(II) atom is located on a twofold rotation axis and is bonded to four N atoms at distances of 2.037â (8) and 2.109â (9)â Å, and to two S atoms at a distance of 2.406â (3)â Å, leading to a distorted octa-hedral coordination. The angle between the mean planes of the coordinating moieties of the two symmetry-related tridentate ligands is 83.3â (2)°. In the crystal, complex mol-ecules are linked by weak C-Hâ¯S hydrogen bonds, π-π inter-actions between the pyridine rings [centroid-centroid distance = 3.775â (9)â Å] and C-Hâ¯π inter-actions. The hydrogen-bonding inter-actions lead to the formation of layers parallel to (010); π-π inter-actions link these layers into a three-dimensional network.
RESUMEN
X-ray crystallography unequivocally confirmed the stereochemistry of the 2-C-methyl group in the title mol-ecule, C(10)H(16)O(5), in which the 1,5-lactone ring exists in a boat conformation. The absolute stereochemistry was determined by the use of d-ribose in the synthesis. The crystal exists as O-Hâ¯O hydrogen bonded chains of mol-ecules running parallel to the a axis with each mol-ecule acting as a donor and acceptor for one hydrogen bond.
RESUMEN
The relative stereochemistry of the title compound, C(10)H(15)N(3)O(5), was confirmed by the crystal structure determin-ation. The absolute configuration was determined from the use of d-lyxonolactone as the starting material. The six-membered ring adopts a boat conformation with the larger azide group, rather than the methyl group, in the bowsprit position. In the crystal structure, a bifurcated inter-molecular O-Hâ¯O/O-Hâ¯N hydrogen bond links mol-ecules into chains running parallel to the b axis.
RESUMEN
X-ray crystallography defines the relative configuration at the three-stereogenic centres in the title compound N-benzyl-l-XYLNAc, C(14)H(20)N(2)O(3). The five-membered pyrrolidine ring adopts an envelope conformation with the N atom lying out of the plane of the other four atoms. In the crystal structure, inter-molecular O-Hâ¯O, N-Hâ¯O and O-Hâ¯N hydrogen bonds link the mol-ecules into chains along [100]. The carbonyl group O atom acts as an acceptor for a bifurcated hydrogen bond. The absolute configuration is determined by the use of l-glucuronolactone as the starting material for the synthesis.
RESUMEN
In the title compound, C(13)H(21)N(3)O(6), the six-membered ring adopts a twist-boat conformation with the azide group in the bowsprit position. The azide group is disordered over two sets of sites in a 0.642â (10):0.358â (10) ratio. The crystal structure consists of O-Hâ¯O hydrogen-bonded trimer units. The absolute configuration was determined from the use of d-mannose as the starting material.
RESUMEN
The title compound, C(22)H(25)F(5)N(4)O(9), is a stable penta-fluoro-phenyl ester inter-mediate in the synthesis of novel homo-oligomeric structures containing branched carbon chains. The structure is epimeric to the previously characterized dimeric penta-fluoro-phenyl ester with stereochemistry (3R,4R,5R), which was synthesized using d-ribose as starting material. The crystal structure of the title mol-ecule 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 intra-molecular and one inter-molecular, both involving O atoms of the meth-oxy groups. The asymmetric unit contains two independent mol-ecules not related by any pseudo-symmetry operators. The major conformational differences are localized, leading to one mol-ecule 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 mol-ecule [occupancy ratio 0.511â (18):0.489â (18)].
RESUMEN
X-ray crystallographic analysis with Cu Kα radiation established the relative configurations of the stereogenic centers in the title compound, C(15)H(20)N(2)O(5), 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-Hâ¯O and O-Hâ¯O hydrogen-bonded bi-layers, with the terminal methyl and phenyl groups forming a hydro-phobic inter-layer inter-face. Some weak C-Hâ¯O inter-actions are also present.
RESUMEN
The name of one of the authors in the paper by Newton et al. [Acta Cryst. (2004), E60, o909-o910] is corrected.[This corrects the article on p. o909 in vol. 60.].
RESUMEN
The unusual methylene aziridine 6-tert-butyl-3-oxa-2-thia-1-azabicyclo[5.1.0]oct-6-ene 2,2-dioxide, C(9)H(15)NO(3)S, was found to crystallize with two molecules in the asymmetric unit. The structure was solved in both the approximately orthogonal and the oblique settings of space group No. 14, viz. P2(1)/n and P2(1)/c, respectively. A comparison of these results clearly displayed an increase in the correlation between coordinates in the ac plane for the oblique cell. The increase in the corresponding covariances makes a significant contribution to the standard uncertainties of derived parameters, e.g. bond lengths. Since there is yet no CIF definition for the full variance-covariance matrix, there are clear advantages to reporting the structure in the nonstandard space-group setting.
Asunto(s)
Compuestos Aza/química , Aziridinas/química , Óxidos/química , Cristalografía por Rayos X , Modelos Moleculares , EstereoisomerismoRESUMEN
The title compound, C(6)H(12)O(6), also known as d-Tagatose, occurs in its furanose and pyranose forms in solution, but only the α-pyran-ose form crystallizes out. In the crystal, the molecules form hydrogen bonded chains propagating in [100] linked by O-Hâ¯O interactions. Further O-Hâ¯O bonds cross-link the chains.
RESUMEN
The crystal structure of the title compound, C(13)H(14)O(5), establishes (i) the (S) - rather than (R) - configuration at the acetal carbon and (ii) that both the acetal and the lactone form five- rather than six-membered rings; the absolute configuration is determined by the use of 2-C-methyl-d-ribono-1,4-lactone as the starting material. The compound consists of hydrogen-bonded chains of mol-ecules running along the a axis; there are no unusual packing features. Only classical hydrogen bonding has been considered.
RESUMEN
X-ray crystallography unequivocally confirmed the stereochemistry of the C atom at position 2 in the carbon scaffold of the title mol-ecule, C(10)H(18)O(4). The pyran-ose ring exists in a chair conformation with the methyl group on the C atom in the 2 position in an equatorial configuration. The absolute stereochemistry was determined from the starting material. The crystal structure consists of O-Hâ¯O hydrogen-bonded chains of mol-ecules running parallel to the b axis.
RESUMEN
The chemical name of the title compound in the paper by Jenkinson, Fenton, Booth, Fleet & Watkin [Acta Cryst. (2009), E65, o610-o611] is corrected.[This corrects the article DOI: 10.1107/S1600536809006357.].
RESUMEN
The reaction of 5-azido-5-de-oxy-2,3-O-isopropyl-idene-2-C-methyl-d-ribose with N,N-diethyl-2-(dimethyl-sulfuranyl-idene)acetamide gave the title compound, C(15)H(26)N(4)O(5), as the major product arising from initial formation of an epoxide which was subsequently opened by intra-molecular attack of the free 4-hydroxyl group. X-ray crystallography confirmed the relative stereochemistry of the title compound and the absolute configuration was determined by the use of d-ribose as the starting material. The crystal structure contains chains of mol-ecules running parallel to the a axis, being linked by weak bifurcated O-Hâ¯(N,N) hydrogen bonds.
RESUMEN
X-ray crystallographic analysis has established that the major product from the protection of d-glucoronolactone with benzaldehyde is (1S)-1,2-O-benzyl-idene-α-d-glucurono-6,3-lactone, C(13)H(12)O(6), rather than the R epimer. The crystal structure exists as O-Hâ¯O hydrogen-bonded chains of mol-ecules lying parallel to the a axis. The absolute configuration was determined by the use of d-glucuronolactone as the starting material.
RESUMEN
X-ray crystallography confirmed the structure of the title triazole, C(11)H(15)N(3)O(5), formed from a single-step reaction of a sugar azide with a brominated ylid. The absolute configuration was determined by the use of d-ribose as the starting material. The six-membered ring is in a half-chair conformation. The crystal structure exists as chains of O-Hâ¯O hydrogen-bonded moleclues running parallel to the b axis.
RESUMEN
The crystal structure of the title compound, C(6)H(11)NO(5), 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. Mol-ecules are linked by inter-molecular O-Hâ¯O and N-Hâ¯O hydrogen bonds into a three-dimensional network, with each mol-ecule acting as a donor and acceptor for five hydrogen bonds.
RESUMEN
The title mol-ecule, C(7)H(15)NO(5), the major product from selective enzymatic oxidation followed by hydrogeno-lysis of the corresponding azido-heptitol, was found by X-ray crystallography to exisit in a chair conformation with three axial hydroxyl groups. One of the hydroxymethyl groups is disordered over two sets of sites in a 0.590â (3):0.410â (3) ratio. In the crystal, O-Hâ¯O, O-Hâ¯(O,O), O-Hâ¯N and N-Hâ¯O hydrogen bonding occurs.
RESUMEN
X-ray crystallographic analysis of the title hydro-bromide salt, C(10)H(20)N(+)·Br(-), of (1R,2S,3R,5R,8aR)-3-hydroxy-meth-yl-5-methyl-octa-hydro-indolizine-1,2-diol defines the absolute and relative stereochemistry at the five chiral centres in steviamine, a new class of polyhydroxy-lated indolizidine alkaloid isolated from Stevia rebaudiana (Asteraceae) leaves. In the crystal structure, mol-ecules are linked by inter-molecular O-Hâ¯Br and N-Hâ¯Br hydrogen bonds, forming double chains around the twofold screw axes along the b-axis direction. Intra-molecular O-Hâ¯O inter-actions occur.