Acid-catalyzed aromatization of benzene CIS-1,2-dihydrodiols - a carbocation transition-state poorly stabilized by resonance

Acid-catalysed dehydration of 3-substituted benzene cis-1,2-dihydrodiols exhibits a Hammett plot with ρ=–8.2, consistent with reaction via a benzenonium ion-like intermediate; however, correlation of +M resonance substituents such as Me and MeO by σp rather than σ+ constants indicates a marked imbalance between resonance and inductive stabilisation of the transition state.