Which of the following alcohols is expected to have a lowest `pK_(a)` value ?

Options

A. Ethanol
B. Isopropanol
C. 2,2,2-Trifluoroethanol
D. 2-Chloroethanol

Answer

C

Explanation

Lower the `pK_(a)` value stronger is the acid. Groups with `-I` effect increases the acid strength (or decreases the `pK_(a)` value) while groups with `+I` effect decreases the acid strength (or increases the `pK_(a)` value). Further `-I` effect of F is more than that of Cl. Thus 2,2,3-trifluoroethanol (C) has lowest `pK_(a)` value.

Trifluoroethanol has lowest `pK_(a)`.