Eyring differences from Arrhenius

If isotope effects arise solely from the difference between isotopic zero-point energy differentials in the reactant state and transition state, with no role of excited vibrational states, then - A5p) = 0 on the Eyring model and Ah = Ad on the Arrhenius model. Thus ... 

The second, slow reaction was followed for 17 and 23-25 in several solvents at several different reaction temperatures. Arrhenius and Eyring activation parameters for the second, slow reaction observed in the addition of iodine to 17 and 23-25 along with those for the addition of bromine to compound 20 are compiled in Table 2. In the examples of Table 2, the rate of reaction increases as the polarity of the solvent increases from CCI4 to EtOAc to CH3CN. The slow reaction remains first-order in all three solvents. For di-4-methoxyphenyltelluride (24), values of and A// in CH3CN are 20-40 kJ moP lower than in CCI4 or EtOAc. Again, the data from the kinetics studies are consistent with the formation of an ionic intermediate via a dissociative process. 

The first-order rate constants observed for the isomerization at different temperatures are shown in Table 6.10. Calculate Ea for the isomerization from an Arrhenius plot and AH from an Eyring plot. 

Unfortunately, the values of the rate constants of the elementary reactions k) could not be evaluated because of the non-availability of the formation constants K2) at different temperatures. Therefore, the apparent rate constants k andk") are considered to be composite quantities of the rate constants, the protonation constants and the formation constants, respectively. The activation parameters of the second-order rate constants were calculated from the temperature dependence of the rate constants using Arrhenius and Eyring equations by the method of least-squares and are summarized in Table 12.4. Again, the thermodynamic parameters of the protonation constants were evaluated from the well-known thermodynamic methods and are listed in Table 12.5. 

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