The ortho‐effect of substituents upon the kinetics of reactions taking place at a reaction center attached to an aromatic ring has long been a topic of interest. For benzoyl chloride solvolyses, it was shown by Bentley and coworkers that the 2,6‐dimethyl‐derivative followed an ionization pathway with characteristics very similar to those for the solvolyses of p‐methoxybenzoyl chloride. We have carried out a Grunwald–Winstein equation treatment of the solvolyses of 2,6‐dichlorobenzoyl chloride, with similar sized chlorines replacing the methyl groups but now with an overall electron‐withdrawing influence of the ortho‐substituents. In this way the reactivity is moderated and the study can be extended to the important fluoroalcohol‐containing solvents. For the 30 solvents studied, an ionization pathway with a moderate nucleophilic solvation component is indicated. For comparison purposes, the treatment has also been applied to the 2,4‐, 3,4‐, and 3,5‐dichloro‐ derivatives. For the 2,4‐dichloro‐derivative, the two reaction channels are clearly visible and the solvents included for each channel are consistent with their solvent properties. Copyright © 2011 John Wiley & Sons, Ltd.

The ortho effect of the chloro substituents in 2,6-dichlorobenzoyl chloride sufficiently hindered attack on the acyl carbon such that an ionization mechanism was observed over the full range of solvents studied. We now compare this behavior with that of 2,6-difluorobenzoyl chloride. The smaller fluoro substituents allow the dominant pathway to be addition-elimination (association-dissociation) in all solvents except those rich in fluoroalcohol, where ionization is dominant. Ranges of operation for both mechanisms had previously been observed for the parent benzoyl chloride but with a wider ionization range than for the 2,6-difluoro derivative. This indicates that, relative to the parent, the electronic destabilizing influence of the fluorines on acyl cation formation outweighs the steric retardation to attack because of the presence of the two ortho-fluorine atoms. An extended (two-term) Grunwald-Winstein equation treatment of the solvolyses of 2,6-difluorobenzoyl chloride is reported.