Evans-Polanyi plot

FIGURE 1. Evans-Polanyi plot for the H-abstraction reaction by BTNO with selected substrates (EL stands for fluorene). Reprinted with permission from Reference 134. Copyright (2005) American Chemical Society... 

FIGURE 5.5. Evans-Polanyi plot for the reaction of a sodium atom with an alkyl halide RX in the gas phase. 

FIGURE 5.6. Evans-Polanyi plots for reactions of sodium vapor with three different alkyl halides RjX, R2X, and R3X. 

FIGURE 5.7. Bell-Evans-Polanyi plot of energy vs. a reaction coordinate for the reaction of equation (5.70). 

FIGURE 5.8. Bell-Evans-Polanyi plots showing the decrease in selectivity with increasing exothermicity and the corresponding change in structure of the transition state. 

Fig. 10. Evans-Polanyi plot (activation energy vs. R-H bond dissociation energy D(R-H)) for the hydrogen abstraction reactions NH2 + R-H NH3 + R.

The rate constant k(T) = 1.1 x 10 exp[-(9.4 2) kJ morVRT] cm -mol s" for the aromatic hydrocarbon CgHgCHg was measured in an isothermal flow reactor in the temperature range 297 to 542 K and interpreted to be due to hydrogen abstraction, since the activation energy fits an Evans-Polanyi plot for saturated hydrocarbons [151]. The effect of the aromatic ring on the reactivity is mainly due to the reduction of the CH bond energy in the methyl group. 

Logadottir A, Rod TH, N0rskov JK, Hammer B, Dahl S, Jacobsen CJH. 2001. The Br0nsted-Evans-Polanyi relation and the volcano plot for ammonia synthesis over transition metal catalysts. J Catal 197 229. 

Figure 16.3 Equipotential curves representing reactant and product in an electron exchange reaction as a function of a solvent reorganisation coordinate and an internal coordinate, both treated as harmonic. The heavy line represents the classical reaction path (path of steepest descent from the top of the barrier). The dotted line represents the Evans-Polanyi diabatic path , whose energy dependence is determined by the generalised internal coordinate q. In this plot, = 5 and the energy change from to is very close to the energy change from [ (R),...

It is also widely appreciated that extrathermodynamic linear correlations between enthalpy and entropy changes are widespread in nature. The interrelations of G°, AJI° and AS° were probably first discussed at length by Evans and Polanyi (1936, 1937). They were explored in much greater detail twenty-seven years later by Leffler and Grunwald (1963). Particular discussion has revolved around the value (or lack thereof) of so-called isokinetic correlations between enthalpy and entropy changes for various processes. Two questions in particular have prevented the development of widespread interest in isokinetic plots. 

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