The Dianion of Heptalene

Heptalene – a very unstable compound – can be reduced by lithium at −80° into its dianion. 1H‐ and 13C‐NMR. studies indicate that this dianion, contrary to the neutral molecule, has its π‐bonds delocalized. The magnetic field induces in this species a large diamagnetic ring current. The dianion of heptalene is thermally very stable, much more so than the neutral compound. All these observations point to an appreciable stabilization energy associated with the 14°‐electron system; this stabilization energy is probably large enough to impose a planar geometry to this dianion.