Meisenheimer Complexes in SN Ar Reactions: Intermediates or Transition States?

Abstract

Meisenheimer's missing! Anionic σ-complexes, best known as Meisenheimer complexes, have long been assumed to be intermediates in S_N Ar reactions. New evidence now suggests that these intermediates may only be formed in select cases and that a concerted pathway is more common. These claims are supported by ¹² C/¹³ C kinetic isotopes effects, determined using a new method based on ¹⁹ F NMR, and DFT calculations.

Keywords: concerted reactions; density functional calculations; kinetic isotope effect; mechanistic studies; nucleophilic aromatic substitution.