An empirical extension of the Bell-Evans-Polanyi relationship

4 An empirical extension of the Bell—Evans—Polanyi relationship 

So far we have considered only the effect of reaction energy and of the electronic electrophilicity parameter on chemical reactivity. ISM implies that other structural factors, such as force constants and bond lengths, can also play a significant role. Although this may be found in very specific cases, it does not have the generality of the factors previously discussed. 

The empirical approach continues to be a useful source of knowledge, particular in complex systems such as many of those involved in chemical reactivity. This can be extended to employ powerful statistical methods (chemometrics), such as Partial Least Squares and multivariate analysis, to retrieve useful information and predict system response. It has been shown that activation energies of several atom-transfer reactions can be described 

Electronic and thermodynamic effects in the reaction barriers as a function of the reactant and product force constants, for AG =0. 

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