Connection between the average local ionization energy and the Fukui function

The average local ionization energy I ¯ ( r ) and the Fukui function f(r) are conceptually-independent measures of molecular reactive behavior. In this Letter, we use Janak’s theorem to establish a plausible link between I ¯ ( r ) and f(r). In particular, both can generally be expected to identify the same sites as most reactive toward electrophiles.