The Effects of Ring Substituents and Leaving Groups on the Kinetics of S N Ar Reactions of 1‐Halogeno‐ and 1‐Phenoxy‐nitrobenzenes with Aliphatic Amines in Acetonitrile

Rate constants are reported for the reactions of a series of 1‐chloro‐, 1‐fluoro‐ and 1‐phenoxy‐nitrobenzenes activated by CF 3 or CN groups or by ring‐nitrogen with n ‐butylamine, pyrrolidine or piperidine in acetonitrile. The results are compared with results reported previously for more strongly ring‐activated compounds. Decreasing ring activation leads to lower values of k 1 for nucleophilic attack although this may be mediated by reduced steric congestion around the reaction centre. Specific steric effects, leading to rate‐retardation, is noted for the ortho ‐CF 3 group. The 1‐phenoxy compounds are subject to base catalysis and values of k Am / k –1 are reduced relative to more strongly activated compounds. This is likely to reflect increases in values of k –1 coupled with decreases in values of k Am as the proton transfer from zwitterionic intermediates to catalysing amine becomes less thermodynamically favourable. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)