Free energy relationships, classes mechanism

There are two main problems in the use of linear-free-energy relationships The first and largest problem is the determination of the reaction series to which an unknown belongs. Such a deduction from electrochemical behavior is not straightforward Furthermore, there may be several reaction series which may be constructed for a class of compounds depending on solution conditions The slope of the E /2 vs a P -ot would be different at high pH s due to a change in the mechanism of reduction. 

Nucleophilic substitution reactions are one of the most important classes of reactions in organic chemistry. In particular, 8 2 reactions are among the most extensively stndied chemical processes in solution and in the gas phase, both theoretically and experimentally. The history of the study of these reactions closely parallels (and is sometimes responsible for) the development of concepts such as structure-reactivity relationships, linear free-energy relationships, steric inhibition, kinetics as a probe of mechanism, stereochemistry as a probe of mechanism and solvent effects. 

---