Leaving group effects on the mechanism of aromatic nucleophilic substitution (SNAr) reactions of some phenyl 2,4,6‐trinitrophenyl ethers with aniline in acetonitrile

Kinetic studies are reported for the reactions with aniline in acetonitrile of a series of X‐phenyl 2,4,6‐trinitrophenyl ethers [X=H, 2‐, 3‐, 4‐CH3, 2,4‐, 2,6‐(CH3)2, 2‐, 3‐, 4‐NO2, 2,4‐, 2,6‐(NO2)2]. X‐ray crystal structures for X=H, 2,6‐(CH3)2 and 2,6‐(NO2)2 are reported and provide evidence for steric crowding around the 1‐position of these molecules. Nevertheless, the kinetic data show that increasing substitution does not sterically inhibit nucleophilic attack by aniline and an ‘early’ transition state is likely. In general, the reactions are base catalysed; interpreted as rate‐limiting deprotonation of the zwitterionic intermediates. Only with the dinitro derivatives is an uncatalysed reaction involving intramolecular proton transfer observed and when X=2,6‐(NO2)2 this pathway takes all the reaction flux.