Stable Ion Study of Regioisomeric Carboxonium-Substituted Pyrenium Ions: Directive Effects, Charge Delocalization Mode, and Conformational Aspects

Regioisomeric monoacyl- and monobenzoyl-substituted pyrenes are diprotonated in FSO3H·SbF5 (4:1)/SO2ClF to give persistent carboxonium−pyrenium dications, whereas diacetyl- and dibenzoylpyrenes are diprotonated to give dicarboxonium dications. The resulting dications were studied by low-temperature NMR at 500 MHz. Conformational aspects of the carboxonium group in various regioisomers are addressed by a combination of NOED spectra and 2D-NMR and AM1 calculations. Charge delocalization pathways are gauged and compared on the basis of the magnitude of Δδ 13C values.