The radical cation of bicyclo[2.2.l]hepta-2,5-diene (8,9,10-trinorboma-2,5-diene; 1) in CF,CICFCl, and CF,CCl, matrices and that of bicyclo[2.2.2]octa-2,5-diene (2,3-dihydrobarrelene; 2) in CFC1, and CF,CCl, matrices have been studied by ESR and'ENDOR spectroscopy. For It, the coupling constants of the olefinic, methano-bridge, and bridgehead protons are 4.780 M.005, +0.304 f 0.002, and 4 . 0 4 9 M.002 mT, respectively. The hyperfine tensor for the methano-bridge protons is axial, A,, = +0.263 k 0.002 and A, = +0.386 t 0.002 mT, while that for the olefinic protons is orthorhombic, A., = -0.594 t 0.005, A> = 4 , 9 1 3 f 0.005, and A: = 4 . 8 3 4 f 0.005 mT (n parallel to C-H bond; z parallel to 2pz axis). For 2t, the coupling constants of the olefinic, ethanobridge, and bridgehead protons are -0.68 k 0.01, +0.162 k 0.005, and 4.108 f 0.005 mT, respectively. The hyperfine data for lt and 2 t fully support the presentation of their singly occupied orbitals as antisymmetric combinations, b,(n_), of the two bonding ethene n-MO's.
Introduction.
-Bicyclo[2.2.l]hepta-2,5-diene (8,9,10-trinorborna-2,5-diene; 1) and bicyclo[2.2.2]octa-2,5-diene (2,3-dihydrobarrelene; 2) are, after bicyclo[2.2.0]hexa-2,5diene (Dewar benzene), the simplest bicyclic dienes of C," symmetry.