Charge delocalization from cationic substituents into phenanthrene: variation in response among regioisomeric carbocations and carboxonium ions

Abstract

In an effort to assess charge delocalization and stabilities, a series of regioisomeric PAH–C⁺R₂ carbocations (PAH = phenanthrene; R = Me, Ph) were generated from their alcohols by ionization with FSO₃H/SO₂ClF. Model carboxonium ions were also generated by O-protonation of the isomeric acetyl- and benzoyl-phenanthrenes with FSO₃H/SO₂ClF. The delocalization paths and the arenium ion character in the resulting carbocations and carboxonium ions are evaluated via low temperature NMR studies; conformational aspects in the carboxonium ions are also addressed. The resulting cations may serve as models for epoxide ring opening in biologically active dihydro diols of several classes of PAHs for which the diol epoxide activation path is believed to be significant in cancer induction.