The Radical Cations of Bicyclohepta-2,5-diene (8,9,10-Trinorborna-2,5-diene) and Bicycloocta-2,5-diene (2,3-Dihydrobarrelene). An ESR and ENDOR Study

Article abstract of DOI:10.1002/hlca.19890720226

The radical cation of bicyclo<2.2.1>hepta-2,5-diene (8,9,10-trinorborna-2,5-diene; 1) in CF2ClCFCl2 and CF3CCl3 matrices and that of bicyclo<2.2.2>octa-2,5-diene (2,3-dihydrobarrelene; 2) in CFCl3 and CF3CCl3 matrices have been studied by ESR and ENDOR spectroscopy.For 1^+., the coupling constants of the olefinic, methano-bridge, and bridgehead protons are -0.780 +/- 0.005, +0.304 +/- 0.002, and -0.049 +/- 0.002 mT, respectively.The hyperfine tensor for the methano-bridge protons is axial.A<*> = +0.263 +/- 0.002 and A<*> = +0.386 +/- 0.002 mT, while that for the olefinic protons is orthorhombic, A_x = -0.594 +/- 0.005, A_y = -0.913 +/-0.005, and A_z = -0.834 +/- 0.005 mT (x parallel to C-H bond, z parallel to 2p_? axis).For 2^+., the coupling constants of the olefinic, ethano-bridge, and bridgehead protons are -0.68 +/- 0.01, +0.162 +/- 0.005, and -0.108 +/- 0.005 mT, respectively.The hyperfine data for 1^+. and 2^+. fully support the presentation of their singly occupied orbitals as antisymmetric combinations, b₂(?), of the two bonding ethene ?-MO's.