FIRST EXAMPLES OF FLUORINATED AND CHLORINATED POLYCYCLIC AROMATIC HYDROCARBON (PAH) DICATIONS FROM BENZO[A]PYRENE, PYRENE, AND THEIR ALKYL-SUBSTITUTED DERIVATIVES

Two-electron oxidations (SbF5/SO2ClF) of 6-fluoro-benzo[a]pyrene, 3, 6 -chloro-benzo[a]pyrene 4, and their corresponding 7-methyl derivatives 5 and 6 as well as 1-fluoropyrene,;7, 1-chloropyrene, 8, and 1-fluoro -2,7-di-tert-butylpyrene, 9, allowed the charge delocalization mode, s ubstituent effects, one-bond and long-range C/F coupling constants, an d the tropicity of the resulting persistent PAH dications to be examin ed by NMR for the first time. For comparison, detailed NMR studies of the dications of 7-methylbenzo[a]pyrene, 2, and the parent benzo[a]pyr ene, 1, are also reported. Total deshieldings Sigma Delta delta C-13 i n the resulting dications are ca. 195-211 ppm/e for the benzo[a]pyreni um and ca. 200-209 ppm/e for the pyrenium dications, respectively. The ir AM1-calculated Delta Delta H(f)degrees values are between 421 and 4 27 kcal/mol and 444 and 449 kcal/mol, respectively, well within the pr eviously predicted dication formation limit of 463 +/- 4 kcal/mol.