Energy Sequence of the Lowest Antibonding Orbitals in Symmetrical Didehydro[n]annulenes with n = 4N+2

A model of a perturbed n‐membered perimeter (n = 4N + 2) is used to interpret the ESR.‐data for the radical anions of symmetrical tetra‐t‐butyl‐didehydro[n]annulenes with n = 14, 18, 22 and 26 (N = 3, 4, 5 and 6). The singly occupied orbital of such radical anions correlates with one of the doubly degenerate, lowest antibonding perimeter MO's which have been classified as symmetric (ΨS) or antisymmetric (ΨA) with respect to the mirror plane passing through two opposite centres and perpendicular to the plane of the perimeter. The relevant MO is ΨS for n = 14 (N = 3) and 22 (N = 5), but ΨA for N = 18 (N = 4) and 26 (N = 6), in accordance with the prediction of the model. It has been shown that the introduction of two symmetrically placed triple bonds into a (4N + 2)‐membered perimeter should stabilize ΨS and destabilize ΨA when N is odd, whereas the reverse should hold when N is even.