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941.
Ohne Zusammenfassung 相似文献
942.
Udo Werner 《Rheologica Acta》1964,3(3):184
Ohne Zusammenfassung 相似文献
943.
944.
945.
Udo Kaatze 《Journal of Molecular Liquids》2011,162(3):105-112
Broadband dielectric spectra of a variety of aqueous solutions are evaluated as to indications of water that may be considered bound. Static permittivity decrements due to depolarizing internal electric fields, from kinetic depolarization, as well as from dielectric saturation are discussed. The latter effect reflects the preferential orientation of water permanent dipole orientations within strong Coulombic field of small ions, especially multivalent cations. Such water may be considered bound even though rapid rotations around the orientation of the electric dipole moment are definitely possible and also a fast exchange of water molecules between the hydration region and the bulk may take place. Water exhibiting large dielectric relaxation times, as typical for regions with large local concentration of foreign matter, may also be named bound. However, no clear evidence for interaction energies exceeding the hydrogen bond energy of pure water has been found. Rather enhanced relaxation times at low water content reflect the small concentration of hydrogen bonding sites and thus low probability density for the formation of a new hydrogen bond. Potential interferences of the water relaxation with relaxations from other molecules or from ionic structures are mentioned briefly. 相似文献
946.
947.
Su KJ Pačar M Mieusset JL Arion VB Brinker UH 《The Journal of organic chemistry》2011,76(18):7491-7496
Foiled carbene structures comprising strong stabilizing interactions between the divalent carbon and the intramolecular double bond have been located by DFT calculations. These tetracyclic species bearing fused five-membered rings impeding intramolecular rearrangements are theoretically predicted to lie in a deep potential energy well. A suitable dibromocyclopropane precursor for this type of foiled carbene has been prepared in 12 steps. Its treatment with methyllithium led to the isolation of a product of a formal carbene dimerization, a bicyclopropylidene. 相似文献
948.
Levy E Puzenko A Kaatze U Ben Ishai P Feldman Y 《The Journal of chemical physics》2012,136(11):114503
In this, the second part of our series on the dielectric spectrum symmetrical broadening of water, we consider ionic aqueous solutions. If in Part I, dipole-dipole interaction was the dominant feature, now ion-dipole interplay is shown to be the critical element in the dipole-matrix interaction. We present the results of high-frequency dielectric measurements of different concentrations of NaCl/KCl aqueous solutions. We observed Cole-Cole broadening of the main relaxation peak of the solvent in the both electrolytes. The 3D trajectory approach (described in detail in Part I) is applied in order to highlight the differences between the dynamics and structure of solutions of salts on one hand and dipolar solutes on the other hand. 相似文献
949.
The reaction of the NHC iPr2Im [NHC=N‐heterocyclic carbene, iPr2Im = 1, 3‐bis(isopropyl)imidazolin‐2‐ylidene] with freshly prepared NiBr2 in thf or dme results in the formation of the air stable nickel(II) complex trans‐[Ni(iPr2Im)2Br2] ( 2 ). Complex 2 was structurally characterized. Thermal analysis (DTA/TG) reveals a very high decomposition temperature of 298 °C. Reduction of 2 with sodium or C8K in the presence of the olefins COD (cyclooctadiene) or COE (cyclooctene) affords the highly reactive compounds [Ni2(iPr2Im)4(COD)] ( 1 ) and [Ni(iPr2Im)2(COE)] ( 4 ). Alkylation of 2 with organolithiums leads to the formation of trans‐[Ni(iPr2Im)2(R)2] [R = Me ( 5 ), CH2SiMe3 ( 6 )], whereas the reaction of 2 with LiCp* [Cp* = (η5‐C5(CH3)5)] at 80 °C causes the loss of one NHC ligand and affords [(η5‐C5(CH3)5)Ni(iPr2Im)Br] ( 7 ). 相似文献