Factors Contributing to the Energy of Reaction

Of these, the first and last terms are quickly dealt with. 

In pairs of similar reactions, the bonds involved in the two reactions are those in the corresponding reaction centers, which are by nature similar. The term will therefore be the same or nearly the same for both processes and will cancel in the expression for the relative equilibrium constant [equation (4.10)]. 

This point can be easily illustrated. Take, for example, the protonation of a pair of even AHs [cf. equation (4.6)]. The only localized bonds undergoing any change in the reaction are those formed by the carbon atom to which the proton is to be attached i.e.. 

Now Ecu and 5 ch will be the same for substitution at different positions in different hydrocarbons. Since the CC bond lengths in aromatic hydrocarbons vary very little, the terms 5Eqc will also be much the same since they represent the difference in bond energy between a CC sp -sp a bond compressed to the aromatic length of 1.4 A and a normal sp -sp a bond. All the terms in equation (4.14) should therefore be much the same for attack at different points in different hydrocarbons, so their sum, AE, should be likewise constant. 

The last term in equation (4.12) refers to changes in solvation energies. 

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