On the importance of charge alternation

The concept of stabilization of polyanionic and polycationic compounds by charge alternation was introduced to explain the course of polymetalation of hydrocarbons and enolates. This concept is generalized to the positional stabilization of polar compounds containing two or more donor or acceptor groups and reconciled with the different known stabilizations of compounds containing a donor and an acceptor group. Various properties of other classes of compounds such as relative acidities and basicities of heterocyclic compounds, charge distribution in cyanines, mesocyanines,oxonoles and aromatic dianions, as well as the regioselectivity of some reactions seem also to obey the rules based on this concept.