Femtosecond Nucleophilic Substitution Reaction Dynamics

A general class of reactions termed aromatic nucleophilic (S_NAr) is central to organic syntheses, reaction mechanisms, and electron transfer processes. A textbook example is the following reaction which is generally considered as a two-step process, the addition of the nucleophile (a → b) and the elimination to form final products (b → c). However, if the processes of addition and elimination are concerted, the so-called σ-complex (b) becomes a transition state, similar in nature to S_N2 reactions.