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71.
72.
An innovative one‐step procedure for the synthesis of 4‐hydroxybenzofuran and an improved synthesis of 5‐hydroxybenzofuran is reported. Such compounds were also transformed into their amino derivatives via Smiles rearrangement with good to high overall yields. 相似文献
73.
74.
V.B. Gavrikov V.P. Likhachev J.D.T. Arruda-Neto A.L. Bonini 《The European Physical Journal A - Hadrons and Nuclei》2001,12(4):487-493
Differential and integral features of incoherent X-radiation, induced by relativistic electrons in crystals, are studied for
observation angles θγ several times greater than γ-1, where γ is the projectile Lorentz factor. The existence of sharp maxima and a minimum of the five-folded incoherent differential
cross-section as a function of the final electron angles, and a dip minimum when the cross-section is taken as a function
of the photon energies, is demonstrated. At near backward observation angles the three-folded cross-section shows a maximum
in the region of several keV photon energies. The obtained results allow us to optimize the conditions for coincidence experiments,
minimizing the incoherent contribution to the total radiation yield, and helping to analyse results of finite-size detector
experiments with crystal targets.
Received: 2 July 2001 / Accepted: 26 November 2001 相似文献
75.
Extraction and gas chromatographic evaluation of plasticizers content in food packaging films 总被引:3,自引:0,他引:3
Cling films are prepared by adding (5-30% w/w) adipates, citrates, and phthalates. The adverse effects on human health of the plasticizers have been demonstrated, and then their content in food contact plastics and possible migration to foodstuffs must be carefully checked. To offer an easier tool to perform these controls, a Soxhlet extraction by ethyl acetate and a multi residue chromatography analysis, with Flame Ionization Detector, have been optimised for the application in evaluating both the real content of plasticizers in films and freezing bags, and their migrated amounts in simulants. The average extraction yield was 95 ± 10%. The chromatographic analysis was able to determine 16 different compounds, clearly separated, taking only 25 min to complete the assay. The detection limits ranged from 0.07 to 0.7% (w/w). The total amount of plasticizers in the packaging products was comprised between 3 and 10% (w/w). Extracted and migrated amounts were compared, and they resulted in good agreement. No migration of Phthalates, whose presence has been demonstrated in some samples, has been observed. It has been also demonstrated that a prolonged contact (till 60 days) did not increase the amount of migrated plasticizers, and then the risks for health. 相似文献
76.
Bianca F Bonini aetano Maccagnani ermana Mazzanti Piero Piccinelli 《Tetrahedron letters》1979,20(41):3987-3990
The reaction of organolithium compounds with stilbene episulphoxides and episulphides leads to stereospecific desulphurization and to ring opening. The stereochemistry of the latter reaction depends on the structural features. 相似文献
77.
A new asymmetric synthesis of R-(?)- and S-(+)- mevalonolactones is described. Starting from a single achiral precursor, the synthesis proceeds by a nine-steps sequence, Sharpless epoxidation of an appropriate allylic alcohol. 相似文献
78.
Alessandro Degl'innocenti Bianca Bonini Germana Mazzanti Antonella Capperucci M. Cristiana Ferrara Alfredo Ricci 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):365-366
Abstract Fluoride ion induced reaction of allyl- and benzyl-silanes with thiocarbonyls leads, contrary to the corresponding lithium or Grignard reagents, to products of S-functionalization. 相似文献
79.
In this paper we take an approach similar to that in [13] to establish a positive mass theorem for spin asymptotically hyperbolic
manifolds admitting corners along a hypersurface. The main analysis uses an integral representation of a solution to a perturbed
eigenfunction equation to obtain an asymptotic expansion of the solution in the right order. This allows us to understand
the change of the mass aspect of a conformal change of asymptotically hyperbolic metrics.
Vincent Bonini: The first named author supported by MSRI Postdoctoral Fellowship.
Jie Qing: The second named author supported partially by NSF grant DMS 0402294.
Submitted: April 6, 2007. Accepted: September 24, 2007. 相似文献
80.
Both symmetrical and nonsymmetrical trans-2,3-diaryloxiranes are regio- and stereoselectively opened by the LiBr/Amberlyst 15 system. In the case of symmetrical trans-stilbene oxide, the syn- versus anti-bromohydrins ratio ranged between 88/12 and 30/70, by varying the reaction temperature from 20 to -30 degrees C. In the case of nonsymmetrical para-substituted trans-2,3-diaryloxiranes, the regioselectivity is determined by electronic effects. If one phenyl bears a strong electron-withdrawing group (as NO2 or CF3), the nucleophilic attack is totally on the beta-carbon with respect to the substituted phenyl ring. With one phenyl bearing a strong electron-releasing group (OCH3), the regioselectivity is reversed. Ab initio calculation at the DFT/B3LYP/6-31G level, run on protonated epoxide structures, supports the formation of a cationic acyclic intermediate. Application of the method on ortho-methoxy and ortho-nitro 2,3-diaryloxiranes afforded the syn-bromohydrins in excellent yield, via regio- and stereoselective opening at either alpha- or beta-carbon, respectively. 相似文献