With the M06-2X functional, no TS could be located for this dissociation reaction. Interestingly, however, a barrier can readily be recovered when switching over to the M06 functional, as a shallow minimum -corresponding to a loose complex -is formed at this level of theory. The computed M06 barrier amounts to 11 kcal/mol, which agrees with the approximate dissociation energy inferred from a relaxed scan along the C-O bond axis with the M06-2X functional (see Section S2 of the Supporting Information). As such, one can reasonably expect the carbocation to be thermally accessible in acidic solution (see Section S3 of the SI for a more in-depth discussion).