排序方式: 共有48条查询结果,搜索用时 15 毫秒
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Lopez JM Männle F Wawer I Buntkowsky G Limbach HH 《Physical chemistry chemical physics : PCCP》2007,9(32):4498-4513
Using dynamic NMR spectroscopy, the kinetics of the degenerate double proton transfer in cyclic dimers of polycrystalline (15)N,(15)N'-di-(4-bromophenyl)-formamidine (DBrFA) have been studied including the kinetic HH/HD/DD isotope effects in a wide temperature range. This transfer is controlled by intermolecular interactions, which in turn are controlled by the molecular conformation and hence the molecular structure. At low temperatures, rate constants were determined by line shape analysis of (15)N NMR spectra obtained using cross-polarization (CP) and magic angle spinning (MAS). At higher temperatures, in the microsecond time scale, rate constants and kinetic isotope effects were obtained by a combination of longitudinal (15)N and (2)H relaxation measurements. (15)N CPMAS line shape analysis was also employed to study the non-degenerate double proton transfer of polycrystalline (15)N,(15)N'-diphenyl-formamidine (DPFA). The kinetic results are in excellent agreement with the kinetics of DPFA and (15)N,(15)N'-di-(4-fluorophenyl)-formamidine (DFFA) studied previously for solutions in tetrahydrofuran. Two large HH/HD and HD/DD isotope effects are observed in the whole temperature range which indicates a concerted double proton transfer mechanism in the domain of the reaction energy surface. The Arrhenius curves are non-linear indicating a tunneling mechanism. Arrhenius curve simulations were performed using the Bell-Limbach tunneling model. The role of the phenyl group conformation and hydrogen bond compression on the barrier of the proton transfer is discussed. 相似文献
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M. Marinov N. Stoyanov A. Ugrinov S. Angelova I. Wawer M. Pisklak V. Enchev 《Journal of Structural Chemistry》2014,55(3):446-455
The structure of 2-(4-hydroxyphenyl)-substituted indan-1,3-dione and phenalene-1,3-dione is investigated using a combination of solid-state NMR, single crystal X-ray analyses and quantum chemical calculations. It is shown that 2-(4-hydroxyphenyl)-1,3-indandione exists as a diketo tautomer while 2-(4-hydroxyphenyl)-1,3-phenalenedione exists in the enol form. 相似文献
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New solid compounds of Al(III), Ga(III) and In(III) with chrysin were obtained. Their composition and some physicochemical properties were studied by thermogravimetric analysis, UV-vis, infrared and solid state 13C NMR spectroscopies. Upon heating the hydrated compounds M(C15H9O4)3·nH2O decomposed to the oxides. The structure of the compounds was elucidated on the basis of obtained results. 相似文献
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13C CP MAS NMR and GIAO-CHF calculations of coumarins 总被引:1,自引:0,他引:1
13C cross-polarization magic-angle spinning NMR spectra were recorded for a series of solid coumarins. Ab initio calculations of shielding constants were performed with the use of GIAO-CHF method. The combined CPMAS NMR and theoretical approach was successful in characterizing solid-state conformations of coumarins; a relationship sigma (ppm) = -1.032 xdelta + 205.28 (R(2) = 0.9845) can be used to obtain structural information for coumarins, for which solid-state NMR or crystal structure data are not available. 相似文献
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Jarosaw Wawer Joanna Krakowiak Wacaw Grzybkowski 《The Journal of chemical thermodynamics》2008,40(8):1193-1199
Densities of solutions of sodium bromide, sodium perchlorate, sodium tetraphenylborate, and tetraphenylphosphonium bromide in methanol at the temperatures ranging from 283.15 to 313.15 K have been measured. Ultrasound velocities for the above systems at T = 298.15 K have been determined. From the obtained data, the partial molar volumes and the partial molar isentropic compressibilities for electrolytes in solution have been estimated. Division into the ionic contributions has been proposed on the basis of the reference electrolyte method. The existence of the high-volume intermediate shell with an enhanced structure has been suggested. 相似文献
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