Persistance of the Cyclopnane Radical Anions and its Relation to Structure

Reactions of [2N]cyclophanes (N = 2, ⃛6) with solvated electrons in 1,2‐di‐methoxyethane at 193 K have been studied by ESR. and ENDOR. spectroscopy. All but the two most highly bridged cyclophanes (N = 5 and 6) are reduced to paramagnetic species under these conditions. Whereas the radical anions of [2.2]‐paracyclophane and [23](1,2,4)‐ and [24](l,2,4,5)cyclophanes are sufficiently persistent to be characterized by their hyperfine data, those of the remaining five cyclophanes undergo a rapid cyclization to the radical anions of 4,5,9,10‐tetrahydropyrenes. These have been identified as the unsubstituted tetrahydropyrene (from [2.2]‐metacyclophane and [23](l,2,3)cyclophane), the 2,7‐dimethyl‐derivative (from [23](1,3,5)‐ and [24](l,2,3,5)cyclophanes) and the 1,8‐dimethyl‐derivative (from (24l,2,3,4)cyclophane). The persistence of the cyclophane radical anions seems to depend on the numbers, nmeta and npara, of the meta‐and para‐positions of the bridging ethano groups in the two benzene rings. The prerequisite for the radical anion to be persistent is nmeta⩽npara.