The charge alternation concept: Application to cyclic conjugated doubly charged systems

The application of the charge alternation concept to the charge distribution in doubly charged ions of mono- and polycyclic molecules (Figure 1) is described. The charge density in the systems under investigation was determined both by calculations and experiments (¹³C NMR). The charges are not distributed uniformly over the entire system but appear in an alternating mode. This charge alternation—a basic characteristic of these systems—is a result of maximum donor–acceptor interactions which stabilize the systems. Rules are derived which enable the prediction of the charge distribution in the system without any need for elaborate calculations.