The Dianions of Pyrene and Pyrene Isomers as (4n)π‐Perimeters

Metal reduction of pyrene and of pyrene isomers under carefully controlled conditions yields the corresponding dianions. The properties of the neutral compounds and of the dianions are studied via 1 H‐NMR. spectroscopy. Whereas the former exhibit similar behaviour, the charge distribution within the dianionic species proves to be very different. As a consequence, some of the polycyclic dianions can be regarded essentially as (4n)π‐perimeters, an approach which is satisfactorily rationalized by simple MO‐models. Further evidence in favour of this bonding scheme comes from the ESR. spectroscopic measurement of the spin density distribution within the corresponding radical anions.