Perimeter‐Type Structures in Charged [4n + 2] Annuleno [4n + 2] annulenes. The Importance of the Frontier‐Orbitals

The tetra(tert‐butyl)[14]annuleno[14]annulene 1 is transformed, via alkali metal reduction, into its radical monoanion, dianion, radical trianion, and tetraanion. The paramagnetic species are characterized by ESR and ENDOR spectroscopy and the diamagnetic species by 1H‐ and 13C‐NMR spectroscopy. Well‐resolved ESR and NMR spectra can only be obtained, if the reduction is carefully monitored. For the interpretation of the data, the ions derived from the structurally related [14]‐ and [22]annulenes 3 and 5 as well from the tetra(tert‐butyl)[14]annuleno[18]annulene 2 serve as suitable model compounds. While the behavior of the neutral annulenoannulene 1 is governed by that of the [14]annulene‐subunit, the corresponding ionic systems can best be described as macrocyclic perimeters. This outcome can be rationalized by the nodal properties of the frontier MO's.