The stepwise binding energies (&UDelta; H°(n-1,n)) of 1-8 water molecules to benzene(•+) [Bz(•+)(H2O)(n)] were determined by equilibrium measurements using an ion mobility cell. The stepwise hydration energies, &UDelta; H°(n-1,n), are nearly constant at 8.5 ± 1 kcal mol(-1) from n = 1-6. Calculations show that in the n = 1-4 clusters, the benzene(•+) ion retains over 90% of the charge, and it is externally solvated, that is, hydrogen bonded to an (H2O)(n) cluster. The binding energies and entropies are larger in the n = 7 and 8 clusters, suggesting cyclic or cage-like water structures. The concentration of the n = 3 cluster is always small, suggesting that deprotonation depletes this ion, consistent with the thermochemistry since associative deprotonation Bz(•+)(H2O)(n-1)+ H2O → C6H5• + (H2O)nH(+) is thermoneutral or exothermic for n ≥ 4. Associative intracluster proton transfer Bz(•+)(H2O)(n-1) + H2O → C6H5•(H2O)(n)H+ would be also exothermic for n a 4, but lack of H/D exchange with D2O shows that the proton remains on C6H6•+ in the observed Bz(•+)(H2O)n clusters. This suggests a barrier to intracluster proton transfer, and as a result, the [Bz(•+)(H2O)(n)]* activated complexes either undergo dissociative proton transfer, resulting in deprotonation and generation of (H2O)(n)H+, or become stabilized. The rate constant for the deprotonation reaction shows a uniquely large negative temperature coefficient of k = cT(-67± 4) (or activation energy of -34 ± 1 kcal mol(-1)), caused by a multibody mechanism in which five or more components need to be assembled for the reaction.