The Halogenation of Aromatic Carbinols

In recent years many efforts have been made aiming to define the conditions of the reaction of substitution which lead to inversion of configuration (Walden inversion). The investigations in this direction of Polanyi et al.,’ of Olson,2 of Hughes, Ingold, et aL3 are most outstanding. Polanyi et al. and Olson came to the conclusion that all reactions of substitution by a negative group or ion are connected with inversion of configuration. On the other hand, Hughes, Ingold, et al. envisaged three possibilities for substitution by a negative ion: inversion, racemization, and retention of configuration, depending on the mechanism of the reaction. Reactions which follow kinetically a bimolecular course are always connected with inversion; those following a monomolecular course may be connected with inversion, racemization, or retention, the inversion always being associated with extensive racemization. These conclusions were accepted also by Steigman and Hammett.4 The concluding lines of the paragraph in which Hughes, Ingold,