The Radical Ions of Dipleiadiene (Dicyclohepta(de,ij)naphthalene) and Its 12b,12c-Homo Derivative. An ESR and ENDOR Study.

The radical anions and the radical cations of dipleiadiene (dicyclohepta[de,ij]naphthalene; 1) and its 12b, 12c-homo derivative 2 were characterized by ESR and ENDOR spectroscopy. Their singly occupied orbitals are related to the degenerate nonbonding MOs of a 16-membered π-perimeter. The π-spin distribution over the perimeter is similar in the radical cations 1.+ and 2.+, and an analogous statement holds for the radical anions 1.− and 2.−. However, deviations of the π-system from planarity lead to a decrease in the absolute values of the negative coupling constants of the perimeter protons in 2.+ and 2.− relative to those in 1.+ and 1.−. The hyperfine data for the perimeter protons in the radical ions correlate with the changes in 13C chemical shifts on passing from the neutral compounds to the corresponding diions. It is concluded from the coupling constants of the CH2 protons in the radical ions of 2 that the cation 2.+ exists in the methano-bridged form (A) of the neutral 2 (and, presumably, also of the dication 22+), whereas the anion 2.− adopts the bisnorcaradiene form (B) of the dianion 22−.