THE FUKUI FUNCTION OF AN ATOM IN A MOLECULE - A CRITERION TO CHARACTERIZE THE REACTIVE SITES OF CHEMICAL-SPECIES

The principle of hard and soft acids and bases is interpreted as the r esult of two opposing tendencies, one related to the charge transfer p rocess (chemical potential equalization principle), and the other one related to the reshuffling of the electronic density (maximum hardness or minimum softness principle). A local version of the principle is e lucidated by assuming that these tendencies are dominated by the local properties rather than by the global properties of the molecule. This principle is used together with the Fukui function of the atoms in th e molecule to characterize the reactive sites. The results presented f or the nucleophilic addition to the pyridinium ion, and for the electr ophilic substitution on pyridine oxide show the usefulness of these co ncepts in describing the inherent reactivity of chemical species.