The “|Δμ| big is good” rule, the maximum hardness, and minimum electrophilicity principles

We show the relation between the “|Δμ| big is good” rule and the maximum hardness and the minimum electrophilicity principles. We focus on a double-exchange acid–base (e.g., charge transfer) reaction. We then prove that the species favored by the “|Δμ| big is good” rule are those such that the multiplication of their hardnesses is the biggest, while the validity of the minimum electrophilicity principle requires other conditions.