Proton-Transfer Dynamics in Protonated Benzene

The proton-transfer reaction mechanism in protonated benzene was examined using ab initio molecular dynamics, paying special attention to cooperative motions. We first examined the lifetime of each stable state of protonated benzene, taken as equal to the time lag between proton-transfer reactions. The theoretically obtained lifetime distribution shows non-statistical behavior, since it contains a large number of short lifetime trajectories. By analyzing the nature of these short trajectories, we found that a transferred proton can be trapped between two carbon atoms. Because carbon atoms adjacent to the transferred proton will change their hybridization during proton-transfer reactions, and since it requires tens of femtoseconds to reform hybrid orbitals, the proton will oscillate between the two carbon atoms without bonding to either. We refer to this trapped state as a “dynamically stable trapped state” and consider that such states may appear in many types of chemical reactions.