Enthalpy-entropy compensation plots

Effusive beam technique, 157-158 Electron bombardment flow radiolysis, 238 Electrospray ionization and ionic clusters, 168 Enantiomers, separation techniques, 154-155 Enantioselectivity of enzymes, 148 Enthalpy-entropy compensation plots, 261 Enthalpy of activation, and quantum tunneling, 67, 70-71... 

The excellent enthalpy-entropy compensation plot, obtained by using AA// R and AAS R values, confirms that the enantiodifferentiation mechanisi is not altered by a change in solvent [37,38]. Judging from the clearly segregal activation parameters obtained in polar solvents (positive AA// R and AA5 and nonpolar solvents (negative AA// R and AAS R), this unprecedented so]... 

Plots of the standard entropy, or better standard free energy, against the standard enthalpy referred to as enthalpy-entropy compensation plots, are a useful tool for establishing the similarity of the retention mechanism for different solutes [25,79,83,95,96]. When enthalpy-entropy compensation occurs the plots are linear and the slope is called the compensation temperature. All compounds have the same retention at the compensation temperature, although their temperature dependence may differ. This is most likely to occur for processes governed by a single retention mechanism. All related processes... 

Certainly, one should be careful in selecting high-quality experimental data for an enthalpy-entropy compensation plot, particularly when limited sets of data are available, since an apparent compensation plot may arise from the experimental errors in measurement, as emphasized by Houk et al. [108]. However, the review of reliable experimental data by Williams et al. [109], as well as the theoretical consideration by Gilson et al. [110, 111] discussed below in detail, leave no doubts about the validity of the enthalpy-entropy compensation relationship itself. 

Fig. 8.6. Clo bal enthalpy-entropy compensation plots for complexation of a wide variety of guests with a- (O), jS- (A), and y-CyD ( ).

Recently, experimental confirmation of the Grunwald theory was achieved by comparison of the quality of differential enthalpy-entropy compensation plots for the exchange equilibrium between (R)- and (S)-enantiomers of chiral guests in ff CyD cavities (Eq. (9)) [82], and the exchange equilibrium between native fi-CyXi and 6-ammonio-6-deoxy-jg-CyD (am- 8-CyD) for chiral and achiral guests (Eq. (10)) [119] ... 

Fig. 8.8. Differential enthalpy-entropy compensation plots for the process of transfer of a CyD complex from H2O to D2O.

FIGURE 2.6 Enthalpy-entropy compensation plots for the water/CPC/alkane (C6, C9) microemulsions. , 1-butanol , 2-butanol , 2-methyl-l-butanol , 1-propanol , 1-hexanol. 

The formation of enthalpically controlled 1 1 and 2 1 (host guest) complexes between a-cyclodextrin and Ph-Me sulfides has been observed in a kinetic and thermodynamic study of the a-cyclodextrin-mediated reaction of substituted Ph-Me sulfides with j-CPBA and peroxomonosulfate. The enthalpically controlled 1 1 cyclodextrin- j-CPBA complex is also formed. Peroxomonosulfate does not form any such complex. The reaction rates are analysed using the transition-state pseudoequilibrium approach. Enthalpy-entropy compensation plots for transition-state pseudoequilibrium constant Kjs give slopes close to unity." ... 

Fig. 10. Enthalpy-entropy compensation plot of several enantiomer pairs interacting with -CD. Reproduced with permission from Ref. [30]. Copyright 2005, Am. Chem. Soc.

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