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11.
A paradigm shift in rate determining step from single electron transfer between phenylsulfinylacetic acids and iron(III) polypyridyl complexes to nucleophilic attack of water to the produced sulfoxide radical cation: a non‐linear Hammett 下载免费PDF全文
Perumal Subramaniam Jebamoney Janet Sylvia Jaba Rose Rajasingh Jeevi Esther Rathinakumari 《Journal of Physical Organic Chemistry》2016,29(10):496-504
Mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAAs) by iron(III) polypyridyl complexes in aqueous acetonitrile medium has been investigated spectrophotometrically. An initial intermediate formation between PSAA and [Fe(NN)3]3+ is confirmed from the observed Michaelis–Menten kinetics and fractional order dependence on PSAA. Significant rate retardation with concentration of [Fe(NN)3]3+ is rationalized on the basis of coordination of a water molecule at the carbon atom adjacent to the ring nitrogen of the metal polypyridyl complexes by nucleophilic attack at higher concentrations. Electron‐withdrawing and electron‐releasing substituents in PSAA facilitate the reaction and Hammett correlation gives an upward ‘V’ shaped curve. The apparent upward curvature is rationalized based on the change in the rate determining step from electron transfer to nucleophilic attack, by changing the substituents from electron‐releasing to electron‐withdrawing groups. Electron‐releasing substituents in PSAA accelerate the electron transfer from PSAA to the complex and also stabilize the intermediate through resonance interaction leading to negative reaction constants (ρ). Conversely, electron‐withdrawing groups, while retarding the electron transfer exert an accelerating effect on the nucleophilic attack of H2O which leading to low magnitude of ρ+ compared to high ρ? values of electron‐releasing groups. Marcus theory is applied, and a fair agreement is seen with the experimental values. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
12.
An experiment is discussed in which CO can be excited up to energies of several electronvolts by the absorption of infrared radiation from a relatively low-power CO laser. Furthermore, experimental results are examined through kinetic modelling. In the experiment, the beam of an intracavity-chopped CO laser operating on all lines at 500 mW and containing a few milliwatts of the fundamental ν= 1→0 band component, is focused into an absorption cell containing a mixture of CO and Ar. The absorption of this infrared radiation is monitored by the optoacoustic effect. A second CO laser operating cw and capable of providing 8 W on all lines but not lasing on the ν= 1→0 band component, is then focused into the same volume in the absorption cell. With both lasers simultaneously focused into the absorption cell, strong fluorescence from the irradiated region is detected by a photomultiplier tube. Modulation of the signal intensity with time is observed, and indicates chemical destruction of the CO in the cell. An analysis and kinetic modelling calculation of this experiment shows that it is possible to excite CO up to high vibrational quantum numbers (ν40) at gas temperatures up to 800 K. by means of CO laser irradiation at the fundamental ν= 1→0 band component. One source responsible for the fluorescence signal observed in the experiment is identified as the 4th positive A 1Π→X 1Σ+ spontaneous emission. Although the present kinetic model does not incorporate the chemical processes that may lead to the production of additional fluorescing species such as C2, good agreement is obtained with the observed fluorescence signal characteristics. 相似文献
13.
Numerical simulations and laboratory measurements have been used to illuminate the interaction of a moving shock wave impacting
on metallic grids at various shock strengths and grid solidities. The experimental work was carried out in a large scale shock
tube facility while computational work simulated the flow field with a time-dependent inviscid and a time-dependent viscous
model. The pressure drop measured across the grids is a result of two phenomena which are associated with the impact of the
shock on the metallic grids. First are the reflection and refraction of the incoming shock on the grid itself. This appears
to be the main inviscid mechanism associated with the reduction of the strength of the transmitted shock. Second, viscous
phenomena are present during the reflection and refraction of the wave as well as during the passage of the induced flow of
the air through the grid. The experimental data of pressure drop across the grid obtained in the present investigation are
compared with those obtained from computations. The numerical results slightly overpredict the experimental data of relative
pressure drop which increases substantially with grid solidity at fixed flow Mach numbers. The processes of shock reflection
and refraction are continuous and they can be extended in duration by using thicker grids that will result in lower compression
rates of the structural loading and increase the viscous losses associated with these phenomena which will further attenuate
the impacting shock. Preliminary theoretical analysis suggests that the use of a graded porosity/solidity material will result
in higher pressure drop than a constant porosity/solidity material and thus provide effective blast mitigation.
相似文献
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R. Garg C. Narayanan D. Lakehal S. Subramaniam 《International Journal of Multiphase Flow》2007,33(12):1337-1364
The Lagrangian–Eulerian (LE) approach is used in many computational methods to simulate two-way coupled dispersed two-phase flows. These include averaged equation solvers, as well as direct numerical simulations (DNS) and large-eddy simulations (LES) that approximate the dispersed-phase particles (or droplets or bubbles) as point sources. Accurate calculation of the interphase momentum transfer term in LE simulations is crucial for predicting qualitatively correct physical behavior, as well as for quantitative comparison with experiments. Numerical error in the interphase momentum transfer calculation arises from both forward interpolation/approximation of fluid velocity at grid nodes to particle locations, and from backward estimation of the interphase momentum transfer term at particle locations to grid nodes. A novel test that admits an analytical form for the interphase momentum transfer term is devised to test the accuracy of the following numerical schemes: (1) fourth-order Lagrange Polynomial Interpolation (LPI-4), (3) Piecewise Cubic Approximation (PCA), (3) second-order Lagrange Polynomial Interpolation (LPI-2) which is basically linear interpolation, and (4) a Two-Stage Estimation algorithm (TSE). A number of tests are performed to systematically characterize the effects of varying the particle velocity variance, the distribution of particle positions, and fluid velocity field spectrum on estimation of the mean interphase momentum transfer term. Numerical error resulting from backward estimation is decomposed into statistical and deterministic (bias and discretization) components, and their convergence with number of particles and grid resolution is characterized. It is found that when the interphase momentum transfer is computed using values for these numerical parameters typically encountered in the literature, it can incur errors as high as 80% for the LPI-4 scheme, whereas TSE incurs a maximum error of 20%. The tests reveal that using multiple independent simulations and higher number of particles per cell are required for accurate estimation using current algorithms. The study motivates further testing of LE numerical methods, and the development of better algorithms for computing interphase transfer terms. 相似文献
16.
Dispersion of spray droplets and the modulation of turbulence in the ambient gas by the dispersing droplets are two coupled phenomena that are closely linked to the evolution of global spray characteristics, such as the spreading rate of the spray and the spray cone angle. Direct numerical simulations (DNS) of turbulent gas flows laden with sub-Kolmogorov size particles, in the absence of gravity, report that dispersion statistics and turbulent kinetic energy (TKE) evolve on different timescales. Furthermore, each timescale behaves differently with Stokes number, a non-dimensional flow parameter (defined in this context as the ratio of the particle response time to the Kolmogorov timescale of turbulence) that characterizes how quickly a particle responds to turbulent fluctuations in the carrier or gas phase. A new dual-timescale Langevin model (DLM) composed of two coupled Langevin equations for the fluctuating velocities, one for each phase, is proposed. This model possesses a unique feature that the implied TKE and velocity autocorrelation in each phase evolve on different timescales. Consequently, this model has the capability of simultaneously predicting the disparate Stokes number trends in the evolution of dispersion statistics, such as velocity autocorrelations, and TKE in each phase. Predictions of dispersion statistics and TKE from the new model show good agreement with published DNS of non-evaporating and evaporating droplet-laden turbulent flow. 相似文献
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Bhabak KP Satheeshkumar K Jayavelu S Mugesh G 《Organic & biomolecular chemistry》2011,9(21):7343-7350
In the present study, the synthesis and characterization of a series of N-methylimidazole-based thiourea and selenourea derivatives are described. The new compounds were also studied for their ability to inhibit peroxynitrite (PN)- and peroxidase-mediated nitration of protein tyrosine residues. It has been observed that the selenourea derivatives are more efficient than the thiourea-based compounds in the inhibition of protein nitration. The higher activity of selenoureas as compared to that of the corresponding thioureas can be ascribed to the zwitterionic nature of the selenourea moiety. Single crystal X-ray diffraction studies on some of the thiourea and selenourea derivatives reveal that the C=S bonds in thioureas possess more of double bond character than the C=Se bonds in the corresponding selenoureas. Therefore, the selenium compounds can react with PN or hydrogen peroxide much faster than their sulfur analogues. The reactions of thiourea and selenourea derivatives with PN or hydrogen peroxide produce the corresponding sulfinic or seleninic acid derivatives, which upon elimination of sulfurous/selenous acids produce the corresponding N-methylimdazole derivatives. 相似文献
20.
Kalaivani Subramaniam Amit Das Dagmar Steinhauser Manfred Klüppel Gert Heinrich 《European Polymer Journal》2011,47(12):2234-2243
This paper focuses on the influence of ionic liquid on carbon nanotube based elastomeric composites. Multi-walled carbon nanotubes (MWCNTs) are modified using an ionic liquid at room temperature, 1-butyl 3-methyl imidazolium bis (trifluoromethylsulphonyl) imide (BMI) and modified MWCNTs exhibit physical (cation–π/π–π) interaction with BMI. The polychloroprene rubber (CR) composites are prepared using unmodified and BMI modified MWCNTs. The presence of BMI not only increases the alternating current (AC) electrical conductivity and polarisability of the composites but also improves the state of dispersion of the tubes as observed from dielectric spectroscopy and transmission electron microscopy respectively. In addition to the hydrodynamic reinforcement, the formation of improved filler–filler networks is reflected in the dynamic storage modulus (E′) for modified MWCNTs/CR composites in amplitude sweep measurement upon increasing the proportion of BMI. Hardness and mechanical properties are also studied for the composites as a function of BMI. 相似文献