Aqueous binary mixtures, variations

Figure 3. Variation of the standard molar free energy of transfer of n-Bu4NBr from water to aqueous binary mixtures at 298.15°K...

Figure 7. Variations of aggregation numbers for ionic and non-ionic micelles in aqueous binary mixtures at 298.15 K...

If the reaction takes place in an aqueous solution, the temperature variation method can be used. The thermal expansion coefficient of water strongly depends on the temperature, and in particular, it vanishes at 4°C. Therefore, the signal observed at this temperature should come from the volume effect (volume grating). Of course, it also includes the population grating or other effects except for the thermal effect, and these contributions should be subtracted. When organic solvents are the media, a series of solvents or binary mixtures of solvents, which do not affect the other reaction parameters (such as the quantum yield, the volume change, the... 

Solvent Structure. There has been some discussion of the importance of solvent structure in kinetics, for example in connection with aquation of cobalt(m) complexes in binary aqueous mixtures. There are difficulties in squaring the kinetic parameters for dimethylformamide and for dimethyl sulphoxide exchange at iron(u) with Bennetto and Caldin s model of solvent structural effects, but this model proved useful in discussion of the aquation of [Co(NH3)s(DMSO)] + in binary aqueous mixtures. Bulky hydrophobic groups in solvent molecules have an effect on solvent structure which is reflected in the kinetics of complex formation. - For dissociative solvent exchange at some M + ions, activation enthalpies appear to be determined by the solvation enthalpy of the metal ion and the solvent structure as manifested in its enthalpy of vaporization. In the reaction of Ni + with malonate, the range of solvent variation of activation parameters is comparable with their likely errors, preventing the authors from discussing their results in terms of Bennetto and Caldin s theories. ... 

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