Activation free frequency factor

Usually, only the Arrhenius energy of activation, E, is given in these papers it differs from the heat of activation,JH, by RT (about 0.6 kcal at ordinary temperatures). Only a few entropies of activa-tion, JS, were calculated the frequency factor, whose logarithm is tabulated, is proportional to this reaction parameter. It is clear that the rate, E, and JS determined for an 8jfAr2 reaction are for the overall, two-stage process. Both stages will contribute to the overall results when their free energies of activation are similar. 

Both the frequency factor and the energy of activation are far smaller than for the other cyclopropane isomerizations discussed so far. The small frequency factor suggests a very rigid transition complex, in which the free rotation of the methyl and vinyl groups has been lost. The postulated complex is shown below. 

Because of the limitations imposed by activity coefficients and specific interactions, a precise quantitative check of experimental data against the collision formula presented here is not possible. However, the frequency factors of bimolecular reactions which are diffusion-controlled (i.e., those which occur on nearly every collision) such as free radical recombinations,... 

The steric and frequency factors of reactions of free radicals with one another or with small molecules are rather alike, and the activation energies are very low for exothermic reactions and only barely higher than the standard-enthalpy changes AH0 for endothermic steps. In simple cases this makes it possible to use thermochemical data to identify which of the many possible steps dominate kinetics. 

Free energy of activation, 207, 210 Free induction decay, 170 Free radical reactions, 8 Frequency, 153, 155 exchange, 167 precessional, 155, 165 relaxation, 167 resonance, 164 Frequency domain, 170 Frequency factor, 188... 

The isomerization of 8 -HOABA and 37 was observed as a first-order reaction in which the rate was proportional only to the concentration of the 8 -hydroxyl compound. As the pH and temperature increased the reaction proceeded more rapidly. At 25°C, the half-life of 8 -HOABA was 30 hr at pH 3, 4 hr at pH 7, and shorter than 1 min at pH 10, that is, 8 -HOABA was isomerized to PA more rapidly at pH 10 than at pH 3 by a fa.ctor of 2,000. The temperature dependence of the rate was greater under alkaline conditions than under acidic conditions. The Arrhenius plots of the rate constants gave the activation energies of Arrhenius and frequency factors, which were converted to the kinetic parameters, i.e. the activation enthalpy activation entropy (4S ) and activation free... 

---