organic compounds
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The title compound, C19H24O6, is a sesquiterpene lactone isolated from the Kenyan plant Warburgia ugandensis. Ring A adopts a chair conformation, ring B is in a C2 twist conformation and the lactone ring is nearly planar with maximum deviation 0.007 (1) Å. The reported absolute configuration is based on that of the similar compound bromo-parasiticolide A and is supported by analysis of Bijvoet differences from light atoms in Mo Kα radiation.
organic compounds
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The title compound, C11H13NO2Si, is a low-temperature form of the previously reported room-temperature structure [Garcia et al. (1998). Acta Cryst. C54, 489-491]. At 298 K, the material crystallizes in the space group Pnma and occupies a crystallographic mirror plane, but at 100 K the space group changes to P212121, the volume decreases by 5% and the molecule distorts. The greatest molecular distortions from Cs symmetry are rotations of the trimethylsilyl and nitro groups by 10.56 (8) and 11.47 (9)°, respectively, to the benzene mean plane. At low temperature, the crystal also becomes an inversion twin, the refined ratio of the twin components being 0.35 (15):0.65 (15).
organic compounds
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The title compound C20H20O4S, is polymorphic. In the tetragonal form, the molecule lies on a crystallographic twofold axis, while the monoclinic form has only approximate C2 molecular symmetry. The greatest excursion from C2 symmetry is in the orientation of the two phenyl rings; at 100 K, one of the rings is rotated -37.2 (3)° and the other by 46.9 (3)° from their symmetric (tetragonal) positions. There are only minor differences in the three-ring nucleus; the best molecular fit of the tetragonal and monoclinic forms, both at 100 K and excluding phenyl rings and H atoms, shows an r.m.s. deviation of 0.066 Å. Both forms have the same absolute configuration.
organic compounds
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The title compound, C18H14O, is polymorphic at 123 K. The orthorhombic form reported herein has two independent molecules in the asymmetric unit, with molecular volume 313.5 Å3. The previously reported triclinic (P-1) form [Raston & Scott (2000). Green Chem., 2, 49–52] has molecular volume 309.6 Å3 at the same temperature. All three molecules deviate significantly and systematically from the putative Cs symmetry (δr.m.s. = 0.0265, 0.0256, 0.0497 Å). Comparison of the two molecules in the orthorhombic polymorph shows that 16 of the 19 equivalent pairs of framework atoms have a mirror-image pattern of deviations (above/below plane), suggesting that the two are quasi-enantiomorphs. The pattern of deviations in the triclinic form is nearly the same (13 of 19 atom pairs) as the orthorhombic form.
organic compounds
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The title compound, C15H13N5, crystallizes with two independent molecules in the asymmetric unit. The molecular conformations are stabilized by C—HN contacts forming S(6) ring motifs. In the crystal, pairs of molecules are connected into R22(12) dimers by N—HN hydrogen bonds. C—Hπ interactions and π–π stacking interactions [centroid–centroid distances = 3.6085 (8), 3.6657 (8), 3.4745 (8) and 3.5059 (8) Å] also also observed.
organic compounds
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In the title compound, C10H9N5, the phenyl ring is twisted with respect to the pyrazole ring, forming a dihedral angle of 24.00 (6)°. In the crystal, molecules are linked by N—HN hydrogen bonds into chains running parallel to [010] containing alternating R22(6) and R22(12) rings. Further interactions are found in the crystal, viz. N—Hπ(phenyl) interactions and weak face-to-face π–π stacking interactions [centroid–centroid distance = 3.8890 (6) Å] between the centroids of the pyrazole and phenyl rings are observed.
organic compounds
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The title compound, C24H26O2Si2, has C2 crystallographic symmetry. The dihedral angle between the aromatic rings is 84.5 (2)°. The acetylene group is slightly non-linear, with angles at the acetylene C atoms of 175.7 (2) and 177.0 (2)°. In the crystal structure, only van de Waals interactions occur.
organic compounds
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The title compound, C13H15ClN2O6, was synthesized by hypochlorous acid-mediated chlorination of N-acetyl-3-nitro-L-tyrosine ethyl ester. The OH group forms an intramolecular O—HO hydrogen bond to the nitro group and the N—H group forms an intermolecular N—HO hydrogen bonds to an amide O atom, linking the molecules into chains along [100]. The crystal studied was a non-merohedral twin, with a 0.907 (4):0.093 (4) domain ratio.