ELECTROPHILIC AND OXIDATIVE CHEMISTRY OF 4-METHYL[6]HELICENE, [6]HELICENE AND CORONENE - PERSISTENT ION GENERATION IN SUPERACID MEDIA, GAS-PHASE MASS-SPECTROMETRIC STUDIES AND AM1 CALCULATIONS

4-Methyl[6]helicene 3 is protonated in FSO3H-SO2 at C-3 to give a pers istent-methylhexahelicenium cation; there is minor competing oxidation . The monoarenium ion of parent [6]helicene 2 was observed in the less oxidizing CF3SO3H (TfOH)-SO2CIF. Competing oxidation is extensive and the arenium ion slowly disappears from the NMR spectrum. A monoproton ated coronene cation could not be observed. The coronene radical catio n formed in attempted protonation was characterized by EPR. The proton ation, acetylation and trimethylsilylation of coronene and the [6]heli cenes were studied in the gas phase by Cl-MS and the decomposition of the resulting adducts were examined by tandem mass spectrometry. The o xidations of 1-3 were also probed by El-MS and MS-MS experiments. The energies of arenium ions of protonation of 2-3 were calculated by the AM1 method. The monocations observed under stable ion conditions are n ot the theoretically predicted lowest energy arenium ions. AM1 calcula tions were also performed on coronene radical cation, and its singlet and triplet dications. The previously observed singlet dication is pre dicted to be less stable than the triplet dication by 6.54 kcal mol-1. dagger