Effect of some electron-withdrawing substituents from the meta- and para-positions in aromatic nucleophilic replacement reactions

Abstract

Arrhenius parameters have been measured for the reactions of 3- and 4-trifluoromethyl-, 3,5-bistrifluoromethyl-, and 3- and 4-methylsulphonyl-fluorobenzenes with methoxide ions in methanol. In the meta-series, the log A function is characteristic of the group present, and a comparison with the Arrhenius parameters for the reactions of 3-X-5-nitrobenzenes shows that the effect of disubstitution on the activation energies and the free energies of activation is not additive.

Evidence is presented for the operation of a –E effect in reactions involving the p-methylsulphonyl and p-trifluoromethyl groups.