Linear Gibbs-energy relationships LFER

The Hammett equation is the best-known example of a linear free-energy relationship (LFER), that is an equation which implies a linear relationship between free energies (Gibbs energies) of reaction or activation for two related processes10. It describes the influence of polar meta- or para-substituents on reactivity for side-chain reactions of benzene derivatives. 

Linear free energy relationship (LFER) — For various series of similar chemical reactions it has been empirically found that linear relationships hold between the series of free energies (-> Gibbs energy) of activation AG and the series of the standard free energies of reactions AGf, i.e., between the series of log fc (k -rate constants) and log K (Kt - equilibrium constants) (z labels the compounds of a series). Such relations correlate the - kinetics and -> thermodynamics of these reactions, and thus they are of fundamental importance. The LFER s can be formulated with the so-called Leffler-Grunwald operator dR ... 

Such relationships are usually referred to as linear free energy relationships (LFER). The appropriateness of this term may easily be seen. For equilibria, equation (1) applies, where is the standard free energy (Gibbs energy) of reaction. 

This expression reveals the existence of a linear relation between energy barrier and reaction energy. When expressed in terms of Gibbs energy, this represents a linear free-energy relationship (LFER). 

The Kc values measured in CCI4 are significantly lower than tliose in alkanes, except in the case of selenoethers. It was not possible to find a general relationship between the Kc values determined in these two solvents. However, linear Gibbs energy relationships of good precision were found [84] for families of structurally related bases. The LFER equation is... 

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