Kirkwood correlation plots

Initiator decomposition studies of AIBN in supercritical C02 carried out by DeSimone et al. showed that there is kinetic deviation from the traditionally studied solvent systems.16 These studies indicated a measurable decrease in the thermal decomposition of AIBN in supercritical C02 over decomposition rates measured in benzene. Kirkwood correlation plots indicate that the slower rates in supercritical C02 emanate from the overall lower dielectric constant (e) of C02 relative to that ofbenzene. Similar studies have shown an analogous trend in the decomposition kinetics ofperfluoroalkyl acyl peroxides in liquid and supercritical C02.17 Rate decreases of as much as 30% have been seen compared to decomposition measured in 1,1,2-trichlorotrifluoroethane. These studies also served to show that while initiator decomposition is in general slower in supercritical C02, overall initiation is more efficient. Uv-visual studies incorporating radical scavengers concluded that primary geminate radicals formed during thermal decomposition in supercritical C02 are not hindered to the same extent by cage effects as are those in traditional solvents such as benzene. This effect noted in AIBN decomposition in C02 is ascribed to the substantially lower viscosity of supercritical C02 compared to that ofbenzene.18... 

It is expected that the excellence of a correlation should diminish as the correlated process and the model process are made increasingly different in their mechanistic character. Thus, we should not expect great generality from univariate correlations on the other hand, from the quality of the correlation we may be able to leam something about the correlated process. It is not surprising that the rate of one Menschutkin reaction is well correlated with the rate of another Menschutkin reaction, for their mechanisms should be very similar. The solvent effect data (8mAG ) in Table 8-10 are poorly correlated with the Kirkwood dielectric constant function, but a plot against Er (30) shows some improvement. - In this... 

The importance of light absorption to directly populate the triplet state in the presence of heavy atoms [(10.271)] and the effect of heavy atoms on the phosphorescence of acenaphthylene [(10.27m)] are easily ruled out. No new absorption bands or increased band intensities are noted in the presence of heavy atoms. Since no phosphorescence is observed, even at low temperature, there cannot be an important effect on this process. A heavy-atom effect on the partitioning of reactions (10.27g,h) and (10.27k) is eliminated by the data of Hartmann, Hartmann, and Schenck in their study of solvent effects on the photosensitized photolysis of acenaphthylene. The influence of a number of solvents was described with the use of Kirkwood-Onsager solvent parameters (an empirical method for the correlation of reaction rate with the ability of the solvent to stabilize the change in dipole moment in proceeding to the transition state). A linear plot of log(fra/u/cw) vs. the expression [(Z) — 1)/(2Z) -f- where D is the dielectric constant, p is... 

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