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81.
82.
Abboud JL Castaño O Dávalos JZ Jiménez P Gomperts R Müller P Roux MV 《The Journal of organic chemistry》2002,67(4):1057-1060
The standard enthalpy of formation of gaseous 2-adamantyl chloride(2-Ad-Cl) was determined by calorimetric techniques. The standard Gibbs energy change for the chloride anion exchange between 1-adamantyl (1-Ad+) and 2-adamantyl (2-Ad+) cations in the gas phase was obtained by Fourier transform ion cyclotron resonance spectroscopy (FT ICR). Theoretical calculations at the G2(MP2) level were performed on these and other relevant species. This and data from the literature provided three highly consistent independent estimates of the relative stabilities of 2-Ad+ and 1-Ad+. This difference in gas-phase stability was compared to the differential structural effects on the rates of solvolysis of the corresponding chlorides and tosylates, and it was shown that the thermodynamic stability of the secondary cation is the leading factor determining the solvolytic reactivity of the precursors in the absence of solvent effects. Thus, under these conditions, the previously established linear free energy correlation between carbenium ion stability and solvolytic reactivity of bridgehead derivatives applies also to secondary derivatives. 相似文献
83.
Herman Zagppey Roel H. Fokkens Steen Ingemann Nico M. M. Nibbering Helena Florencio 《Journal of mass spectrometry : JMS》1991,26(6):587-594
The regioselectivity of methyl cation transfer from (CH3)2F+, (CH3)2Cl+ and (CH3)3O+ to 1-phenyl-2-aminopropane was studied by Fourier transform ion cyclotron resonance in combination with collision-induced dissociation and neutralization-reionization mass spectrometry of the stable [M + CH3]+ ions formed in a chemical ionization source. The (CH3)2F+ ion transfers a methyl cation to the NH2 group and the phenyl ring with almost equal probability. Predominant CH3+ transfer to the NH2 group is observed for the (CH3)2Cl+ ion whereas the (CH3)3O+ ion reacts almost exclusively at the amino group. The preference for methylation at NH2 is discussed in terms of a lower methyl cation affinity of the phenyl ring than of the amino group and the existence of an energy barrier for methylation of the phenyl moiety. 相似文献
84.
Zaragoza F 《The Journal of organic chemistry》2002,67(14):4963-4964
Treatment of alcohols with an excess of (cyanomethyl)trimethylphosphonium iodide leads, after aqueous hydrolysis, to the clean formation of nitriles with two more carbon atoms than present in the original alcohol. Benzylic, allylic, and aliphatic alcohols without beta-branching (RCH(2)CH(2)OH) have been converted to nitriles with success. The required phosphonium iodide is simple to prepare and can be stored for a long time at room temperature. 相似文献
85.
Ana Fernández-la-Villa Diego F. Pozo-Ayuso Mario Castaño-Álvarez 《Current Opinion in Electrochemistry》2019
Microfluidic and electrochemical technologies have been at the forefront of the development of emerging analytical microsystems. Microfluidics and electrochemistry show a synergistic relationship, empowering their inherent features. Thus, integration of microfluidics and electrochemical (bio)sensors is envisioned as a powerful tandem for boosting the next generation of lab-on-a-chip platforms, including point-of-care and point-of-need systems. In this review, a general overview of the advantages, drawbacks, and gaps as well as remaining challenges and future trends of coupling microfluidics and electrochemical cells is presented. Special attention is given to the manufacturing and scale-up of the integrated devices and all those aspects that can push on the development of true lab-on-a-chip platforms for reaching the industrial domain and actual commercialization. 相似文献
86.
Separation of triadimefon and triadimenol enantiomers and diastereoisomers by supercritical fluid chromatography 总被引:4,自引:0,他引:4
The enantiomeric separation of triadimenol and triadimefon on a Chiralpak AD column using supercritical fluid chromatography, was studied in this work. The effect of different modifiers (methanol, ethanol and 2-propanol) was tested, with methanol and ethanol providing the best results for the enantiomeric separation of the two compounds. The enantioseparation of a mixture of triadimenol and triadimefon (six stereoisomers) was achieved in only 15 min using a gradient of ethanol, 200 bar, 35 degrees C and a flow-rate of 2 ml/min. The separation of triadimenol diastereoisomers on different achiral columns (diol, silica and ODS) was also investigated. In this case, the type of organic modifier to be used depended on the stationary phase, the Spherex Diol being the column that gave the best separation. Using this column, resolutions higher than 3 were obtained in analysis times of 5 min with any of the modifiers checked. 相似文献
87.
A new synthesis of perchlorotolane (perchlorodiphenylacetylene; I) is described. It dimerizes at high temperature to give (III) and (IV). Under the same conditions the latter yields (V). 相似文献
88.
Simultaneous determination of sulfaquinoxaline, sulfamethazine and pyrimethamine by liquid chromatography 总被引:2,自引:0,他引:2
Berzas Nevado JJ Castañeda Peñalvo G Guzmán Bernardo FJ 《Journal of chromatography. A》2000,870(1-2):169-177
A liquid chromatography method is described to determine sulfaquinoxaline (SQX), sulfamethazine (SMT), and pyrimethamine (PMT), by using a Kromasil C18 column and a 40 mM NaH2PO4 buffer solution, containing 10 mM NaClO4 (pH 3.0)–acetonitrile (65:35) as mobile phase. The mobile phase flow-rate and sample volume injected were 1.5 ml/min and 20 μl, respectively and the samples were dissolved in the mobile phase. The limits of quantification were found to be about 180 μg/l (3.6 ng) for each compound. The method was applied in veterinary commercial formulations. Analyses were made by means of the standard addition method, whose results were compared with those obtained by preparing “tests” (from the stock solutions) and with those obtained by a capillary electrophoresis method. Both methods showed similar results, and then it was proved that some commercial claimed levels were not in agreement with the obtained results by using our analytical method, as they were in other cases. 相似文献
89.
J. Rodríguez Flores J. J. Berzas Nevado G. Castañeda Peñalvo M. I. Rodríguez Cáceres 《Chromatographia》2002,56(5-6):283-288
Summary A micellar electrokinetic capillary chromatography (MEKC) method has been developed for quantification of four drugs-tamoxifen,
anastrozole, letrozole, and methotrexate—used to treat advanced breast cancer. Separation was performed at 25°C and 25kV,
with 20mm borate buffer (pH 9.2) containing 40mm sodium dodecylsulfate as electrolyte solution. Under these conditions analyses were performed in 12 min. The linearity of
the response was investigated for the concentration range 2.0–20.0 mg L−1. The intra-day residual standard deviation (n=4 graphs) between the slopes of the calibration graphs was acceptable for the four drugs studied. Detection limits (signal-to-noise
ratio=3) were below 1 mg L−1 for all the compounds. The simplicity, precision, and sensitivity of MEKC proved suitable for quality control of pharmaceutical
preparations used to treat advanced breast cancer. Six different pharmaceutical preparations, each containing one of the above-mentioned
drugs, were successfully analyzed. 相似文献
90.
Dimitri P. Bertsekas David A. Castañon 《Computational Optimization and Applications》1993,2(3):229-259
In this paper we broadly generalize the assignment auction algorithm to solve linear minimum cost network flow problems. We introduce a generic algorithm, which contains as special cases a number of known algorithms, including the -relaxation method, and the auction algorithm for assignment and for transportation problems. The generic algorithm can serve as a broadly useful framework for the development and the complexity analysis of specialized auction algorithms that exploit the structure of particular network problems. Using this framework, we develop and analyze two new algorithms, an algorithm for general minimum cost flow problems, called network auction, and an algorithm for thek node-disjoint shortest path problem. 相似文献