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121.
Leonardo Lo Presti Raffaella Soave Riccardo Destro 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(4):o199-o201
The title compound, (7R,8S)‐7,8‐dihydroxy‐3,7‐dimethyl‐6‐oxo‐7,8‐dihydro‐6H‐isochromene‐5‐carbaldehyde, C12H12O5, is a trans‐vicinal diol. Of the two fused rings, which lie approximately in the same plane, the pyran ring is almost perfectly planar, while the cyclohexenone ring adopts a slightly distorted half‐chair conformation. The crystal packing is dictated by two strong intermolecular O—H⃛O interactions, one involving hydroxy and keto groups, the other involving two hydroxy groups. Molecules are linked together through twofold axes, forming zigzag ribbons extended along the a axis. 相似文献
122.
Carlo Andrea Mattia Alessandra Braca Nunziatina De Tommasi Raffaella Puliti 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(11):o644-o646
The title tetracyclic diterpenoid, 10,13,16,17‐tetrahydroxy‐9‐methyl‐15‐oxo‐20‐norkaurane‐18,10‐carbolactone hemihydrate, C20H28O6·0.5H2O, is a plant metabolite from Parinari sprucei, part of the Venezuelan Amazon flora. The asymmetric unit consists of two nearly identical molecules of the diterpenoid and one molecule of water. Some of the geometric parameters reflect steric strain in the molecule. The extended structure is characterized by hydrogen bonds and weaker hydrogen‐mediated interactions, which involve all of the hydroxy groups and propagate in sheets that coincide with the (002) family of planes. The water molecule acts as a double hydrogen‐bond donor and single acceptor and thus plays a critical role in the pattern of intermolecular interactions. 相似文献
123.
Optimisation of a new headspace mass spectrometry instrument. Discrimination of different geographical origin olive oils 总被引:1,自引:0,他引:1
Cerrato Oliveros C Boggia R Casale M Armanino C Forina M 《Journal of chromatography. A》2005,1076(1-2):7-15
A fast head-space analysis instrument, constituted by an automatic sample introduction system directly coupled to a mass detector without performing any chromatographic separation, was assembled. A suitable and original response was computed to optimise, by experimental design, the measured signals for discrimination purposes. The volatile fractions of 105 extra virgin olive oils coming from five different Mediterranean areas were analysed. The rough information collected by this system was unravelled and explained by well-known chemometrical techniques of display (principal component analysis), feature selection (stepwise linear discriminant analysis) and classification (linear discriminant analysis). The 93.4% of samples resulted to be correctly classified and the 90.5% correctly predicted by cross-validation procedure, whilst the 80.0% of an external test set, created to full validate the classification rule, were correctly assigned. 相似文献
124.
Raffaella Cincinelli Sabrina Dallavalle Lucio Merlini Raffaella Nannei Leonardo Scaglioni 《Tetrahedron》2009,65(17):3465-5823
Acid treatment of indole-2-carboxylic acid β- and γ-oxoamides causes Friedel-Crafts intramolecular cyclization to β-carbolinones and dihydro-2H-azepino[3,4-b]indol-1-ones, in contrast to secondary δ-,?-, and ζ-oxoamides, which cyclize to the novel heterocyclic rings pyrrolizino[2,1-b]indole, indolizino[2,1-b]indole, and 9a,11-diaza-indeno[1,2-a]azulene, via an intermediate N-acyliminium ion. Tertiary amides lead only the Friedel-Crafts ring closure, thus allowing the synthesis of larger fused rings. 相似文献
125.
The kinetic study of the efficient regioselective oxidation of the C? C double bond of 4‐methylcoumarins with isolated dimethyldioxirane was investigated using UV–vis spectroscopy methods. In the excess of dimethyldioxirane, the pyrone ring of a coumarin skeleton is selectively epoxidated and hydroxylated in neutral media, in high yields. Kinetic analyses demonstrate two independent reaction pathways, epoxidation and hydroxylation, respectively, which was also confirmed using kinetic isotope effect methods. Both reaction products were isolated, and their structures were determined by NMR and mass spectra. The position of methyl groups attached at the aromatic part of coumarin molecule shows significant influence on kinetic rate constants and activation parameters. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 414–420, 2009 相似文献
126.
Emiliano Manzo M. Letizia Ciavatta Raffaella Puliti Yue-Wei Guo Guido Cimino 《Tetrahedron》2005,61(31):7456-7460
Three novel halogenated C15-acetogenins, compounds 1-3, have been isolated, together with known metabolites, from a South China Sea collection of the anaspidean mollusc Aplysia dactylomela. The structures have been suggested by both NMR analysis and comparison with literature data. The structure of 1 was confirmed by a single crystal X-ray study, which also allowed the establishment of its absolute stereochemistry. 相似文献
127.
Burgemeister K Franciò G Hugl H Leitner W 《Chemical communications (Cambridge, England)》2005,(48):6026-6028
An inverted supercritical CO2/aqueous biphasic catalytic system allows highly enantioselective hydrogenation of polar water-soluble substrates and efficient recycling of the CO2-philic catalysts. 相似文献
128.
With the proposed fast frequency selective MR imaging (FFSMRI) method, we focused on the elimination of all off-resonance components from the image of the observed object. To maintain imaging speed and simultaneously achieve good frequency selectivity, MRI was divided into two steps: signal acquisition and postprocessing. After the preliminary phase in which we determine imaging parameters, MRI takes place; the signal from the same object is successively acquired M times. As a result, we obtain M partial signals in k-space, from which we calculate the image of the observed object in postprocessing phase, after signal acquisition has been completed. With proper selection of parameters, it is possible to exclude from the image a majority of off-resonance components present in the observed object. However, we can decide to keep only a chosen off-resonance component in the image and eliminate all other components, including the on-resonance component and thus producing a different image from the same acquisition. The experiments with Fe(OH)(3) and oil showed that signal-to-noise ratio (SNR) can be improved by about a factor of four. The proposed FFSMRI method is suitable for frequency selective MR imaging and quantitative measurements in dynamic MRI where exclusion of off-resonance components can improve the reliability of measurement. 相似文献
129.
Raffaella Franci 《Annali dell'Universita di Ferrara》1971,16(1):45-53
Sommario Si da un nuovo metodo per costruire algebre da una data algebra, si studiano le identità che si conservano in questa costruzione
e l'operatore ad essa collegato.
Lavoro eseguito nell'ambito dell'attività dei gruppi di ricerca matematica del C.N.R. contratto n. 115218205174.
Ringrazio il Prof.R. Magari dell'Università di Ferrara sotto la cui guida è stato eseguito questo lavoro. 相似文献
Summary I give a new method for building new algebras from a given algebra, we study identities preserved in this construction and related operator.
Lavoro eseguito nell'ambito dell'attività dei gruppi di ricerca matematica del C.N.R. contratto n. 115218205174.
Ringrazio il Prof.R. Magari dell'Università di Ferrara sotto la cui guida è stato eseguito questo lavoro. 相似文献
130.
[reaction: see text] 6-Phenanthridinones and their heterocyclic analogues were synthesized through a one-pot procedure based on consecutive Pd-catalyzed aryl-aryl and N-aryl coupling from iodoarenes ortho-substituted by electron-releasing substituents and amides of o-bromoarene- and heteroarenecarboxylic acids. 相似文献