The use of perfluoroalkanesulfonic acids and their derivatives in drastic conditions leads us to study their behaviour with respect to temperature and radiative factors.Such acids as CF3SO3H and C2F5SO3H, used in a pure state as well as their related pure anhydride are stable until they reach a temperature of at least 180°C.On the other hand, the solutions of anhydride with its related acid, yield perfluorosulfonic esters and SO2 at room temperature already: This mechanism is discussed.These results involve a new and easy synthesis of symmetrical perfluorosulfonic esters RFSO3RF with acids and P2O5. Further more, it occurs no transformation of the anhydride under UV and visible irradiation. But under the same conditions, a small account of acids are deshydrated into anhydrides.A further experiment combining both effects of temperature and light leads to the esters. 相似文献
The electron impact mass spectrometric fragmentation pathways for some 3-substituted derivatives of coumarin, benzo[f]coumarin, thieno[3,2-f]coumarin, thieno[2,3-h]coumarin and azacoumarin, viz nitriles, carboxamides, thiocarboxamides and esters were investigated. The initial cleavage of the pyrone ring is found to be largely dependent on the stability, under electron impact, of the attached functional group. 相似文献
Nitroaromatics and nitroalkanes quench the fluorescence of Zn(Salophen) (H2Salophen = N,N'-phenylene-bis-(3,5-di- tert-butylsalicylideneimine); ZnL(R)) complexes. A structurally related family of ZnL(R) complexes (R = OMe, di-tBu, tBu, Cl, NO2) were prepared, and the mechanisms of fluorescence quenching by nitroaromatics were studied by a combined kinetics and spectroscopic approach. The fluorescent quantum yields for ZnL(R) were generally high (Phi approximately 0.3) with sub-nanosecond fluorescence lifetimes. The fluorescence of ZnL(R) was quenched by nitroaromatic compounds by a mixture of static and dynamic pathways, reflecting the ZnL(R) ligand bulk and reduction potential. Steady-state Stern-Volmer plots were curved for ZnL(R) with less-bulky substituents (R = OMe, NO2), suggesting that both static and dynamic pathways were important for quenching. Transient Stern-Volmer data indicated that the dynamic pathway dominated quenching for ZnL(R) with bulky substituents (R = tBu, DtBu). The quenching rate constants with varied nitroaromatics (ArNO2) followed the driving force dependence predicted for bimolecular electron transfer: ZnL* + ArNO2 --> ZnL(+) + ArNO2(-). A treatment of the diffusion-corrected quenching rates with Marcus theory yielded a modest reorganization energy (lambda = 25 kcal/mol), and a small self-exchange reorganization energy for ZnL*/ZnL(+) (ca. 20 kcal/mol) was estimated from the Marcus cross-relation, suggesting that metal phenoxyls may be robust biological redox cofactors. Electronic structure calculations indicated very small changes in bond distances for the ZnL --> ZnL(+) oxidation, suggesting that solvation was the dominant contributor to the observed reorganization energy. These mechanistic insights provide information that will be helpful to further develop ZnL(R) as sensors, as well as for potential photoinduced charge transfer chemistry. 相似文献
Heat capacities of -CD·9.7H2O weremeasured by adiabatic calorimetry in the temperature range10–300 K. Differential scanning calorimetry wasused to follow the evolution of the thermalbehaviour versus hydration ratio between 170 and300 K. At least three different behaviours wereobserved, according to the number, n, of watermolecules: 0 < n < 7, 7 < n < 10, and n > 10.These macroscopic results are discussed in terms oforganization differences between the most or theleast hydrated -CD. The structuring effectof the hydration water molecules is emphasised. Theexistence of two energetically distinct -CDhydrates (n < 10 and n > 10) seems to be confirmed. Thishypothesis is discussed in comparison with previousspectroscopic and structural studies. 相似文献
Oyster farming structures are artificial obstacles which disturb tidal flow and wave propagation. These effects can induce modifications of erosion and sedimentation patterns, turbidity changes, local silting up and can be threatening for the shellfish farming itself. The understanding of the impact of these structures in terms of hydrodynamics and sediment dynamics in the far-field, i.e. at the scale of a bay, is a very challenging task.In order to investigate the far-field impact, it is very important to understand in the first place all the changes which occur at a smaller scale, i.e. at the scale of a single table for a farm consisting of oyster tables made of metallic wire structures on which porous bags of oysters are laid. This work is carried out through the idealized representation of the in-situ flow in a free surface flume tank. The flow characteristics around the overall structure are determined from velocity measurements obtained by laser velocimetry. The results highlight an asymmetric development of the boundary layers which suggest the existence of preferential areas for silting up and suspended matter fragmentation under the table. 相似文献
In the case where the charge of the particle is small compared to its mass, we describe the asymptotics of the Lorentz–Maxwell
equation (Abraham model) for any finite-energy data. As time goes to infinity, we prove that the speed of the particle converges
to a certain limit, whereas the electromagnetic field can be decomposed into a soliton plus a free solution of the Maxwell
equation.
It is the first instance of a scattering result for general finite energy data in a field-particle equation.
Submitted: October 31, 2007. Accepted: April 21, 2008. 相似文献
This article is devoted to the study of the nonhomogeneous incompressible Navier-Stokes system in dimension d ≥ 3. We use new a priori estimates, which enable us to deal with low-regularity data and vanishing density. In particular,
we prove new well-posedness results which improve the results of Danchin [6] by considering a less regular initial density,
without a lower bound. Also, we obtain the first uniqueness criterion for weak solutions which is at the scaling of the equation. 相似文献