A Protonated Quinone Methide Stabilized by a Combination of Partial Aromatization and π‑Interaction: Spectroscopic and Crystallographic Analysis

We have expanded
the repertoire of cation−π interactions
to include a carbocation−π system resulting from the
protonation of a π-stacked para-quinone methide
(p-QM). This unusual carbocation is stabilized by a combination of
partial aromatization of the QM moiety and through-space interaction
with the π-system of the adjacent aromatic ring. Single crystal
X-ray analysis of the protonated form reveals a structure consisting
of a hydrogen-bound complex involving two molecules of the precursor
and one proton.