Transition State Theories. Whelands Method

The method of discussing chemical reactivity represented by theories of the type discussed above cannot in general be justified. The rate of a chemical reaction depends on the difference in energy between the reactants and the transition state for the reaction s. In principle, then, it is essential to consider the nature of this transition state rather than merely to concentrate on the nature of the reactants. 

The importance of the transition state in aromatic substitution has long been recognized. Thus Ingold and his co-workers frequently stressed the change in character, from the sp to the tetrahedral configuration, of the 

For pyridine, agreement with experiment follows with any positive value of and positive values of h Khx fers to oxygen atoms, ha to the nitrogen atom, and pai is an adjustment of the resonance integral of the 

This sort of approach can be criticized in several ways. First, of course, it shares the general shortcomings of all theories of reactivity in neglecting steric factors and solvation factors. More particularly, the application of 

Calculations of atom localization energies by Wheland s method have been made by a number of authors and will be considered at appropriate points in this work. 

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