The phrase “linear free energy relationship”(LFER) as applied in organic chemistry to the Hammett equation grew out of the seminal studies of Hammett. 1 Normally such an LFER refers to a linear correlation where a chemical or spectroscopic process is used as a probe. The resultant equilibrium, rate constants, or excitation energies for the processes are then correlated in the presence of a variety of perturbations. As a consequence, substituent ...