Abstract
The radical anion of trans‐10b, 10c‐dihydropyrene (V), which is formed upon reduction of the isomeric [2.2]metacyclophane‐1,9‐diene (III) with solvated electrons, has been identified by its ESR.‐spectrum. The large coupling constant (19.1 Gauss), due to the two equivalent β‐protons in the alkyl bridge, gives evidence of an important hyperfine interaction between the σ‐MO's of the C(sp^3^)‐H bonds and the singly occupied π‐MO of the fourteen‐membered perimeter. This finding supports the assumption that the unexpected energy sequence of the lowest antibonding perimeter MO's in the dihydropyrene V and its 10b, 10c‐dimethyl derivative (VI) is determined by hyperconjugation rather than by the inductive effect of the alkyl bridge.
When the solution of V^○^ in 1,2‐dimethyoxyethane (DME) is brought in contact with an alkali metal mirror, an immediate conversion of V^Φ^ into the radical anion of pyrene (IV) occurs. The anion IV^Φ^ also results from reduction of 2.2.2cyclophane‐1,9,17‐triene (VIII) with potassium in DME, whereas the radical anions of 4,5,9,10‐tetrahydropyrene (II) and its 2,7‐dimethyl‐derivative (IX) are obtained by corresponding reactions of [2.2]metacyclophane (I) and 2.2.2cyclophane (VII), respectively.