Resonance in the Chloracetic Acids

Abstract

IN a letter in NATURE, H. O. Jenkins¹ has discussed the dissociation constants of the chloracetic acids, and concluded that the electrostatic inductive effect cannot account for the strength of the di- and trichloracids, although that of the mono-acid is quantitatively explicable on this basis², since “no functional relationship can be traced between u R (resultant moment of the C-Cl links) and K (dissociation constant)”. This conclusion is, however, incorrect; for, if the bonds are tetrahedrally arranged around their carbon atom, the change in the electrostatic potential at the carboxyl group (which is the inductive effect), should be proportional to the number of C-Cl links present, if μ θ and r remain unchained for each link. That is, we should have where pK is the negative logarithm of K, for x chlorine atoms, pK₀ that of acetic acid, and q a constant; that is, the Ostwald-Wegscheider rule, although the resultant moments of the corresponding chlormethanes are not as 1:2:3.