Complex permittivity measurements on acetophenone and its derivatives o-hydroxybenzaldehyde, o-methylacetophenone, and o-hydroxyacetophenone are performed at frequencies between 1 MHz and 20 GHz at temperatures from 273 to 323 K. The parameters obtained from the fitting of the complex permittivity are analyzed in order to study the effects of the hydroxyl group within a molecule on the dielectric relaxation phenomenon in these liquids. The analysis indicates that dynamical properties are affected not only by the intermolecular hydrogen bond but also by the slight change in molecular structure. This conclusion differs from those obtained from the results of other experiments. 相似文献
Aromatic ketones are enantioseletively hydrogenated in alcohols containing [RuX{(S,S)‐Tsdpen}(η6‐p‐cymene)] (Tsdpen=TsNCH(C6H5)CH(C6H5)NH2; X=TfO, Cl) as precatalysts. The corresponding Ru hydride (X=H) acts as a reducing species. The solution structures and complete spectral assignment of these complexes have been determined using 2D NMR (1H‐1H DQF‐COSY, 1H‐13C HMQC, 1H‐15N HSQC, and 1H‐19F HOESY). Depending on the nature of the solvents and conditions, the precatalysts exist as a covalently bound complex, tight ion pair of [Ru+(Tsdpen)(cymene)] and X?, solvent‐separated ion pair, or discrete free ions. Solvent effects on the NH2 chemical shifts of the Ru complexes and the hydrodynamic radius and volume of the Ru+ and TfO? ions elucidate the process of precatalyst activation for hydrogenation. Most notably, the Ru triflate possessing a high ionizability, substantiated by cyclic voltammetry, exists in alcoholic solvents largely as a solvent‐separated ion pair and/or free ions. Accordingly, its diffusion‐derived data in CD3OD reflect the independent motion of [Ru+(Tsdpen)(cymene)] and TfO?. In CDCl3, the complex largely retains the covalent structure showing similar diffusion data for the cation and anion. The Ru triflate and chloride show similar but distinct solution behavior in various solvents. Conductivity measurements and catalytic behavior demonstrate that both complexes ionize in CH3OH to generate a common [Ru+(Tsdpen)(cymene)] and X?, although the extent is significantly greater for X=TfO?. The activation of [RuX(Tsdpen)(cymene)] during catalytic hydrogenation in alcoholic solvent occurs by simple ionization to generate [Ru+(Tsdpen)(cymene)]. The catalytic activity is thus significantly influenced by the reaction conditions. 相似文献
Three different solvates of TBA6[Nb10O28] (TBA = tetra-n-butylammonium) were structurally characterized. The results revealed that two water molecules are hydrogen-bonded to the terminal oxygens of the [Nb10O28]6− anion in the same manner in all of the solvates. Decaniobate [Nb10O28]6− dimerizes by the action of HCl to form icosaniobate [Nb20O54]8−, while icosaniobate breaks up into decaniobate [Nb10O28]6− by the action of TBAOH. Decaniobate also dimerizes spontaneously to form icosaniobate [Nb20O54]8− in CH2Cl2 even if no acid is added to the solution. The reaction was followed by IR spectroscopy, and the results suggested the reaction is second order with respect to the concentration of [Nb10O28]6−. 相似文献
Switchable molecules : The electronic configurations of the Fe center in trans‐[Fe(tzpy)2(NCS)2] in low‐spin, high‐spin, and LIESST states (LIESST=light‐induced excited spin‐state trapping) were confirmed by K‐ and L‐edge X‐ray absorption and magnetic measurements. The molecular structures at 40 K before and after irradiation are superimposed in the picture, which demonstrates a single‐crystal‐to‐single‐crystal transition by irradiation.
Pyridine attacks : Nucleophilic addition of pyridine derivatives to a doubly linked corrole, which is a stable singlet biradical species, occurs at the bay area with high regioselectivity to provide zwitterionic dimers (see picture; Ar=C6F5). Charge transfer between the anionic corrole and the pyridinium groups induces effective fluorescence quenching of the corrole dimer, which can be utilized for selective fluoride ion recognition.
Mix and match : The pentagonal [Mo6O21]n? polyoxomolybdate building block assembles with other sources of Mo, V, and Sb ions to form an orthorhombic Mo‐V‐Sb oxide. The first single‐crystal X‐ray analysis of an orthorhombic Mo–V‐based oxide, a promising catalyst for light alkane selective oxidation known as the “M1 phase”, revealed the structure of the compound.
We have prepared and isolated neutral polycyclic hydrocarbon radicals. A butyl-substituted radical gave single crystals, in which a π-dimeric structure, not a σ-bonded dimer, was observed, even though steric protection was absent. Thermodynamic stabilization due to the highly spin-delocalized structure contributes effectively to the suppression of σ-bond formation. 相似文献
A novel method for preparing enzyme membranes was developed. The enzyme was attached onto the electrode surface by dropping the enzyme solution and allowing it to dry. Glucose oxidase was used for entrapment. Then, the electrode surface was coated with an ionic liquid containing cellulose, and the ionic liquid was removed by immersing the electrode into water. Enzyme activity was retained in the membrane; the enzyme electrode can be used for detecting glucose in the range of 10 μM to 1 mM, and the response time was ~10 s. The stability duration of the electrode was examined: the enzyme electrode could be used for glucose detection for 6 months. The membrane was observed by atomic force microscopy in the force modulation mode; crystalline and amorphous parts were intermingled. In conclusion, the cellulose membrane can be a suitable immobilization matrix for enzymes. 相似文献
[2.2]Paracyclophane‐based through‐space conjugated oligomers and polymers were prepared, in which poly(p‐arylene–ethynylene) (PAE) units were partially π‐stacked and layered, and their properties in the ground state and excited state were investigated in detail. Electronic interactions among PAE units were effective through at least ten units in the ground state. Photoexcited energy transfer occurred from the stacked PAE units to the end‐capping PAE moieties. The electrical conductivity of the polymers was estimated using the flash‐photolysis time‐resolved microwave conductivity (FP‐TRMC) method and investigated together with time‐dependent density functional theory (TD‐DFT) calculations, showing that intramolecular charge carrier mobility through the stacked PAE units was a few tens of percentage larger than through the twisted PAE units. 相似文献