NMR studies of bridged ring systems: XIX—13C?1H spin coupling and 13C chemical shift of the bridge methylene in benzonorbornene and benzonorbornadiene

Data on ¹³C chemical shifts and ¹³C? ¹H spin coupling constants of norbornane ( 1 ), norbornene ( 2 ), norbornadiene ( 3 ), benzonorbornene ( 4 ) and benzonorbornadiene ( 6 ) are reported. The non-equivalence in J(¹³C? H) values determined from the two bridge methylene proton signals in 2,2,3,3-tetradeuteriobenzonorbornene ( 5 ) and 6 is briefly discussed. The extraordinary deshielding of the bridge methylene carbon in 6 has been noted.