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61.
62.
Baldomero Esquivel Jorge Cardenas Alfredo Toscano Manuel Soriano-Garcia Lydia Rodriguez-Hahn 《Tetrahedron》1985,41(16):3213-3217
From the aerial parts of Salvia fulgens Cav. (Labiatae) a new diterpenoid with a rearranged neo-clerodane skeleton was isolated. This novel compound named salvigenolide, showed a six-seven A/B ring system with a trans fussion. A probable biogenetic route is proposed. Its structure and relative stereochemistry as in , were established by spectroscopic means and X-ray diffraction analysis. 相似文献
63.
64.
Summary The effects of aggregation on the electromagnetic resonance scattering by small, strongly reflecting spheres are studied.
Two or more spheres are allowed to cluster together to form rather complicated anisotropic scatterers whose extinction cross-section
is calculated as a function of the wave number of the incident field in the neighbourhood of the lowest resonance of the individual
spheres. The macroscopic absorption coefficient of a low-density random dispersion of clusters is also calculated in the same
range of wave number. The results for two-, three- and four-sphere clusters are discussed.
Work supported in part by C.N.R. through the G.N.S.M. and in part by the U.S. Army European Research Office through grant
DAJA45-84-C-0005 and contract DAJA37-81-C-0895. 相似文献
65.
Rubén A. Toscano Rachel Mata José Calderon Rosabel Segura 《Journal of chemical crystallography》1996,26(10):707-711
Chloroform/Methanol extraction of the bark ofCedrela salvadorensis (Meliaceae), followed by chromatography afforded the crystalline C28H34O7 terpene. The structure first proposed by spectroscopy is confirmed by this X-ray analysis as 7-acetyloxy-14,15:21,23-diepoxy-4,4,8-trimethyl-d-homo-24-nor-17-oxachola-1,20,22-triene-3,16,-dione. The title compound crystallized in the orthorhombic space groupP212121 with unit cell parametersa=10.243(2),b=13.356(3) andc=18.058(4) Å. The molecule is comprised of a six-membered tetracyclic skeleton, with a circular arc overall conformation. No intermolecular hydrogen bonding is indicated. 相似文献
66.
Marcos Martínez Francisco Lara Ochoa Raymundo Cruz-Almanza Rubén A. Toscano 《Journal of chemical crystallography》1996,26(7):451-456
The title compound crystallizes in a solvent-free form and also includes solvent molecules. The X-ray structure analysis reveals that in the both crystal forms the cyclododecatetraene ring in the host molecules adopts a sofa conformation. The guest molecules occupy the channels formed among columns of stacked host molecules.Contribution No. 1452 of Instituto de Química, UNAM. 相似文献
67.
Manuel Soriano-García Rubén Alfredo Toscano Tessy López Antonio Campero-Celis 《Journal of chemical crystallography》1987,17(6):719-728
The title compound is C35H32NBFe3, monoclinic,P21/n,a=14.204 (4),b=11.582 (4),c=17.547 (6) Å,=101.46 (2)°. The structure was solved by the heavy-atom method and refined by least-squares techniques to anR factor of 0.037 for 3148 observed reflections. The X-ray study confirms that in the solid state the structure of the title compound is similar to that inferred from chemical and spectroscopic evidence. The B atom is coordinated by three ferrocenyl groups and a pyridine ring in a distorted tetrahedral array. The molecule has a nearly three-fold axis normal to the plane defined by the ferrocenyl groups. The B-N distance of 1.656 (5) Å is larger than that obtained for other compounds studied. Bond lengths and angles for the whole structure are all in accord with similar compounds. The pyridine and cyclopentadienyl rings are planar. The H atoms of the cyclopentadienyl rings are displaced significantly toward their corresponding Fe atom. The molecules in the crystal are packed at normal van der Waals distances. No unusually short intermolecular contacts are noted. 相似文献
68.
Jesús Valdés-Martínez Manuel Rubio Raul Cetina Rosado Javier Salcedo-Loaiza Rubén A. Toscano Georgina Espinosa-Pérez Simón Hernandez-Ortega Klaus Ebert 《Journal of chemical crystallography》1994,27(11):627-634
The crystal structure of 5-methyl-acetophenonethiosemicarbazone monohydrate,A, and salicylaldehyde-2-methylthiosemicarbazone monohydrate,B, were determined using single crystal X-ray diffraction.A crystallizes in the monoclinic space groupC2/c, with lattice parametersa=14.161(2),b=15.753(1) ?,c=11.084(1) ?, β=112.59(1)° andZ=4, yielding a calculated density ofD
calc=1.352 mg/m3.B crystallizes in the triclinic space groupP1, witha=7.233(2) ?,b=7.371(2) ?,c=11.841(2) ?, α=82.77(2)°, β=78.33(2)°, γ=63.06(2)° andD
calc=1.371 mg/m3 forZ=2,. In bothA andB the immine nitrogen and the sulfur atom areanti with respect to N2-C8. WhileA presents the usual intramolecular six membered hydrogen bond ring,B has instead an intermolecular hydrogen bond between the hydroxy moiety of the salicyladehyde and a water molecule. AM1 calculations
agree with the experimental conformations observed in both compounds.
Contribution No. 1619 of the Instituto de Química, UNAM. 相似文献
69.
Francesco P. Ballistreri Gaetano A. Tomaselli Rosa M. Toscano 《Tetrahedron letters》2008,49(20):3291-3293
Aromatic and aliphatic thiols are oxidized in acetonitrile at 20 °C by hydrogen peroxide in the presence of methyltrioxorhenium as the catalyst to yield the corresponding sulfonic acids in high isolated yields (85-94%). 相似文献
70.