Annulenes. Part XII. The dianion of [12]annulene

Abstract

[12]Annulene is very unstable and can be reduced by alkali metals at –80° to the corresponding dianion. An n.m.r. study of this species clearly indicates that (i) it has the same perimeter configuration as the parent [12]-21-annulene, (ii) it presents a diamagnetic ring current (14 π-electrons, τ 14·60 for the three inner protons), it is thermally much more stable than the parent [12]-21-annulene, and it does not undergo any dynamical process such as the very fast conformational mobility observed in [12]-21-annulene itself.

All these observations point to an appreciable resonance energy associated with the 14 π-electrons, despite the non-planarity of the ring.