Question

Of the given options, which is (i) the strongest acid, and (ii) which is the potentially chiral acid?

`"a. acetic acid;"`
`"b."` `HClFC-CO_2H`
`"c."` `Cl_2HC-CO_2H`
`"d."` `H_3C-CO_2H`

Answer 1

The answer is `b` for both questions.

Explanation:

I take it that this is a 2nd year inorganic chemistry problem. Halogen substitution on the carboxylic acid reduces the charge density of the carboxylate anion, `RCO_2^-`, which results from protonolysis. Thus the resultant acetate ion is entropically favoured because it is less charge dense and less polarizing.

Note that this is an old problem, and it is well-known that this is an entropy phenomenon.

As to chirality, only chlorofluoroacetic acid bears a chiral centre, which is on the substituted methyl group bound to carboxylate carbon. This carbon has 4 different substituents: the carboxyl group; the hydrogen; and the 2 different halogens.