The Mechanism of Nucleophilic Substitution Reactions at an Iodine Center: Single-Well or Double-Well Potential Energy Surface?

High Resolution Image Download MS PowerPoint Slide Nucleophilic substitution (S N ) reactions belong to the most important transformations in both organic and inorganic chemistry. Although S N reactivity is well-known for many main group elements, its extension to halogen centers is restricted to a few examples, and the mechanism of such reactions lacks fundamental understanding. Recent achievements initiated our investigations to decipher the mechanism of the substitution reactions between various amide ions and elemental I 2 . Here, we present that these reactions follow an addition–elimination pathway through a charge-transfer complex (single-well potential energy surface), opposing a classical bimolecular mechanism via a central transition state (double-well potential energy surface), as reported recently. In addition, inclusion of a continuum solvent model for a polar solvent (such as water) remarkably impacts the thermodynamic feasibility of these reactions. Uncovering the mechanism of these S N 2 reactions is a key step to a general understanding of S N reactions involving other attacking nucleophiles and to possible future extensions toward further halogens.