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871.
The oxidation of several 2-diphenylamino-substituted thiophenes and N,N'-bis(2-diphenylamino-5-thienyl)-substituted phenylene-1,4-diamines with different substitution patterns in the 5-position of their thiophene moieties was studied by cyclovoltammetric and spectroelectrochemical measurements (ESR, UV/Vis/NIR). These measurements revealed both the structure of the oxidation products obtained and that of their cationic intermediates, as well as the pathway of their formation and follow-up reactions. Thus, the formation of the radical cations in the first electrochemical oxidation step of the target molecules was demonstrated. Depending on the substitution pattern, these radical cations give rise to several consecutive processes to a different extent. Thus radical dimers, dehydrodimers with a 2,2-bithiophene, 3,3'-bithiophene, or benzidine structure, as well as radical monocationic and dicationic products can be formed. For N,N'-bis(2-diphenylamino-5-thienyl)-substituted phenylene-1,4-diamines rather stable radical cations and dications were primarily formed and unambiguously identified. These species were transformed into 2,2'-bithiophene dimers and oligomers when the 5-position of the thiophene moiety was unsubstituted. By in situ spectroelectrochemistry the influence of the substituents on the type of coupling reactions can be demonstrated and followed in detail. 相似文献
872.
We have studied the vibrational relaxation of the H(2)O bending mode in an H(2)O:HDO:D(2)O isotopic mixture using infrared pump-probe spectroscopy. The transient spectrum and its delay dependence reveal an anharmonic shift of 55+/-10 cm(-1) for the H(2)O bending mode, and a value of 400+/-30 fs for its vibrational lifetime. 相似文献
873.
Olaf Melsheimer 《Foundations of Physics》1980,10(5-6):375-401
874.
In order to make analytical measurement results traceable to the SI units in the field of clinical chemistry, an ion chromatographic (IC) measurement procedure has been developed which allows the amount of substance of the four so-called electrolytes Na, K, Mg and Ca as well as that of Li to be determined efficiently in human serum and with high accuracy. The IC measurement procedure was validated using primary measurement procedures confirmed by international comparison measurements and is proposed for use as a transfer standard when comparing measurements with clinical reference laboratories. The solutions used for calibration were gravimetrically prepared from pure substances (salts). Their chemical compositions had been iteratively fitted to those of the samples. The serum samples were mineralized by microwave-assisted digestion. The following relative expanded uncertainties for the average elemental contents were obtained: Li 0.4%, Na 0.14%, K 0.6%, Mg 0.8% and Ca 0.4%. 相似文献
875.
876.
Mingliang Xie Wenqing Wang Joëlle De Jonge Olaf Kolditz 《Transport in Porous Media》2007,66(3):311-339
The focus of this work is to provide a new concept for accessing the swelling stress in expansive porous media, especially
in highly compacted bentonite. The key to the new approach is the simulation with a chemical swelling model of an infinitesimal
volume change followed by a back compaction Process. Free extension is allowed in the first step, to calculate the interlayer
porosity change (micro) and the induced volume change potential (macro). The object-oriented FEM simulator GeoSys/RockFlow
allows the combination of different processes. The hydro-mechanic/chemical (H2M/C) model takes into consideration two phase flow and deformation, as well as chemical swelling effects. The negative displacements
on each boundary after the free extension simulation are taken as Dirichlet boundary conditions of the back compaction problem.
The deformation step is simulated in the context of elasto-plasticity using the modified Cam-Clay model. The stresses obtained
by back compaction represent the swelling pressure. A 2D example of compacted bentonite is analyzed with the new H2M/C model. 相似文献
877.
878.
Olaf D. Kinzel Richard G. Ball Courtney K. Maguire Silvia Pesci Vincenzo Summa 《Tetrahedron letters》2008,49(46):6556-6558
An efficient and reliable synthesis of the heterocyclic scaffold methyl-3-hydroxy-4-oxo-4H-pyrido[1,2-a]pyrimidine-2-carboxylate is described. The scope of the synthesis regarding the introduction of substituents on the pyrido-fused ring is explored. 相似文献
879.