Moderately strong phenols dissociate by forming an ion-pair kinetic intermediate.

We show computational evidence that ground-state moderately strong hydroxyarenes (Ar-OH, pKa ∼ 0) dissociate by forming an ion-pair intermediate that lives for 3-5 ps. The concentration of this intermediate is approximately 2 times smaller than that of the un-ionized acid at pH ∼ 0.6 and is characterized by average C-O bond lengths (1.