EPR study of bridgehead‐substituted bicyclo [2.2.2]oct‐1‐yl and triptycyl radicals

4‐Substituted bicyclo [2.2.2] oct‐1‐yl radicals were generated by bromine atom abstraction from the corresponding 1‐bromobicyclo [2.2.2] octanes and observed in solution by EPR spectroscopy. A tendency towards lower a(H_β) and a(H_γ) values for inductively electron‐withdrawing substituents such as OMe and F and towards higher values for electron‐releasing groups such as Me₃Ge and Me₃Sn was observed. For a series of bridgehead radicals, the hfs of β‐hydrogens showed a monotonic increase as the extent of flattening at the bridgehead increased. The EPR data indicated that 4‐substitutents exercised a significant effect at the radical centre, mainly by a through‐bond mechanism. 10‐Substituted triptycl radicals were generated in a similar way but showed no hfs from magnetic nuclei of the substituents. Thus, the triptycyl cage transmitted spin density much less effectively than the bicyclo [2.2.2] octyl cage. Bicyclo [2.2.2] oct‐1‐yl and adamant‐1‐yl radicals added to benzene, tert‐butylbenzene and 1,3‐di‐tert‐butylbenzene to give cyclohexadienyl radicals which were characterized by EPR spectroscopy. Triptycyl radicals and strained bridgehead radicals such as cubyl and bicyclo [1.1.1] pent‐1‐yl gave no detectable cyclohexadienyl radicals under similar conditions. Both bicyclo [2.2.2] oct‐1‐yl and adamant‐1‐yl radicals generated in tert‐butylbenzene showed exclusive meta addition with formation of the corresponding 1‐polycyclo‐3‐tert‐butylcyclohexadienyl radical.