Question

Which acid of each pair shown here would you expect to be stronger?
(i) `CH_(3)CO_(2)H or CH_(2)FCO_(2)H`
(ii) `CH_(2)FCO_(2) or CH_2ClCO_(2)H`
(iii) `CH_(2)FCH_(2)CH_(2)CO_(2)H or CH_(3)CHFCH_(2)CO_(2)H`

Answer 1

Explanation : `CH_(3)` group with +I effect increases the electron density on the oxygen atom in O-H bond in the carboxyl group and cleavage of bond becomes diffcult. It therefore, decreases the acidic strength. The F atom has very strong -I effect. i.e., electron withdrawing influence. It decreases the electron density on the oxygen atom and cleavage of bond becomes easy. The acidic character therefore, increases. It is further related to the
(i) No. of F atoms present in the molecule.
(ii) Relative position of the F atom in the carbon atom chain. In the light of the above discussion.
(i) `CH_(2)FCOOH` is a stronger acid.
(ii) `CH_(2)FCOOH` is stronger acid.
(iii) `CH_(3)CHGCH_(2)COOH` us a stronger acid.