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1.
2.
Alessandro Cecchi Giuditta Bartalucci Cinzia Chiappe Roberto Bianchini 《国际化学动力学杂志》2007,39(4):197-203
The kinetics of the electrophilic bromination of three allylic ethers in a nonprotic solvent, 1,2‐dichloroethane, has been investigated. Two of them followed a prevalent second‐order pathway, while the third one exhibited a classical, clean third order. The second‐order pathway in the first two olefins is attributed to electrophilic assistance of the ethereal oxygen to the attacking bromine molecule. In the molecular bromination of 2,4‐cis‐dimethyl‐8‐oxabicyclo[3.2.1]‐6‐octen‐3‐cis‐ol, opposite temperature dependences were found for the two different kinetic pathways. An exoergonic process for the second‐order reaction was explained by the lesser stability of the bromiranium–bromide ionic intermediate, compared to the bromiranium–tribromide in the third‐order profile. © 2007 Wiley Periodicals, Inc. 39: 197–203, 2007 相似文献
3.
This Review discusses the synthesis and characterization by our Group of new antibiotics belonging to the class of penicillins, cephalosporins and rifamycins with ferrocenyl and 1, 1′-ferrocenilene residues in the molecule. As reactants for 6-aminopenicillanic acid (6-APA) and 7-aminocephalosporanic acid (7-ACA) the following were used: 1, 1-bis(chlorocarbonyl)ferrocene, ferrocenyl sulfochloride, 1, 1′-ferrocenylenedisulfochloride and thioglycolic acids S-modified with ferrocene. In the synthesis of rifamycins, the hydrazides of the thioglycolic acids, S-modified with ferrocene, were employed as nucleophilic agents. The synthesized intermediates were characterized by elemental analysis, TLC, IR, UV and 1H NMR spectra. The characterization of new antibiotics was made by TLC, IR and UV spectral analysis. Biological activity was tested on Gram-negative and Gram-positive bacteria. Good activity is reported towards Gram-positive bacteria in the case of derivatives containing residues of thioglycolic acid S-modified with ferrocene, the antibacterial activity being similar to that of amoxicillin, carbenicillin and cephalothin. All compounds are inactive towards Gram-negative bacteria. 相似文献
4.
Paolo De Lucia J. D. Maitland Wright 《Rendiconti del Circolo Matematico di Palermo》1991,40(3):442-452
Dopo aver dato una definizione di parte convessa di un gruppo topologico, si stabilisce una condizione affinchè il condominio
di una misura sia convesso. 相似文献
5.
Miloslav Duchoň Anatolij Dvurečenskij Paolo de Lucia 《International Journal of Theoretical Physics》1997,36(9):1941-1958
We present a solution to the moment problem for effect algebras, concerning mean values of all powers of an observable concentrated
on the interval [0, 1] for states from a convex set. We give a solution for particular examples, e.g., for the set of all
effect operators. We examine how this problem is related to a socalled E-property. Finally, we give a solution for observables
studied in the operational approach to physical theories. 相似文献
6.
Luigi Ambrosone Lucia Costantino Gerardino D'errico Vincenzo Vitagliano 《Journal of colloid and interface science》1997,190(2):286
The densities and viscosities of binary aqueous mixtures of poly(ethylenoxide)hexanols [C6H13(OCH2CH2)mOH, C6Em] (m= 3, 4, and 5) have been studied in the micellar composition range. For the same surfactants the self-diffusion coefficients in mixtures with heavy water have been determined by the spin-echo pulsed field gradient method. The volumetric data are interpreted by means of the phase separation model, and values of the CMC, volume change, and standard free energy change of micellization are obtained. From the viscosity data the hydration numbers of the surfactant hydrophilic head in the micellar state are computed; they are in agreement with those obtained from HDO self-diffusion data. The surfactant self-diffusion data are used to calculate the apparent micelle radius and the aggregation number. The micellization parameters obtained for the different surfactants are compared and discussed. 相似文献
7.
The title pyridazine 1 was found to react with both 2,3-dihydrofuran (2) and 3,4-dihydro-2H-pyran (9) to give the tetracyclic skeletons 5-8 and the phthalonitrile 12 through the intermediates 4 and 10, respectively. A more complex mechanism was ascertained for the reaction of 1 with the pyrroline 14 which, under suitable conditions, afforded the bicyclic derivative 19 as the predominant product; selective elaborations of this species into the 5,6-dicyanoindoles 22 and 23 are reported. 相似文献
8.
We introduce a new approach to crystal-packing analysis, based on the study of mutual recognition modes of entire molecules or of molecular moieties, rather than a search for selected atom-atom contacts, and on the study of crystal energy landscapes over many computer-generated polymorphs, rather than a quest for the one most stable crystal structure. The computational tools for this task are a polymorph generator and the PIXEL density sums method for the calculation of intermolecular energies. From this perspective, the molecular recognition, crystal packing, and solid-state phase behavior of caffeine and several methylxanthines (purine-2,6-diones) have been analyzed. Many possible crystal structures for anhydrous caffeine have been generated by computer simulation, and the most stable among them is a thermodynamic, ordered equivalent of the disordered phase, revealed by powder X-ray crystallography. Molecular recognition energies between two caffeine molecules or between caffeine and water have been calculated, and the results reveal the largely predominant mode to be the stacking of parallel caffeine molecules, an intermediately favorable caffeine-water interaction, and many other equivalent energy minima for lateral interactions of much less stabilization power. This last indetermination helps to explain why caffeine does not crystallize easily into an ordered anhydrous structure. In contrast, the mono- and dimethylxanthines (theophylline, theobromine, and the 1,7-isomer, for which we present a single-crystal X-ray study and a lattice energy landscape) do crystallize in anhydrous form thanks to the formation of lateral hydrogen bonds. 相似文献
9.
F. Melani L. Cecchi V. Colotta D. Catarzi G. Filacchioni 《Journal of heterocyclic chemistry》1992,29(4):819-823
The synthesis of the new tricyclic heteroaromatic system 5H-1,2,4-triazolo[5,1-c][1,4]benzodiazepine, diazaanalogue of 5H-pyrrolo[2,1-c][1,4]benzodiazepine, which is the common feature of some antitumor antibiotics, is reported. The structure of the new tricyclic system and of some of its key intermediates is assigned by means of nuclear magnetic resonance studies. 相似文献
10.
Cr. Simionescu Tatiana Lixandru Lucia Tǎtaru I. Mazilu M. Vâţǎ 《Journal of organometallic chemistry》1982,238(4):363-381
The synthesis and study of some polyenes, polýiminoimides and Schiff polybases with ferrocene obtained by either polymerization or polycondensation are reported.The following monomers were used: ethynylferrocene, 1-chloro-1′-ethynyl-ferrocene, α-chloro-β-formyl-p-ferrocenylstyrene, p-ferrocenylphenylacetylene, p-ferrocenylacetophenone, 1,1′-diacetylferrocene and 1,1′-bis[β-(2-furyl)acryloyl]ferrocene which were characterized by spectral and thermodifferential analyses and Hückel MO calculations. The polymerization was performed in the presence of benzoyl and lauroyl peroxides, triisopropylboron and complex catalysts of [P(C6H5)3]2 NiX2 type. The ferrocene derivatives were polycondensed with biuret, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl thioether, 4,4′-diamino-2,2′-dinitrodiphenyl disulphide in the presence of metallic salts and p-toluene sulphonic acid as catalysts.Polymers with either linear or tridimensional structure showing good thermal stability and semiconducting properties have been obtained. Some polymers show catalytical activity in the polymerization of chloroformylated vinylic derivatives. 相似文献