Question

Among $2$-chloropropanoic acid, $3$-chloropropanoic acid, $2,2$-dichloroacetic acid and propanoic acid the $K_a$ values will be in the order,

• A. $2,2$-dichloroacetic acid > $2$-chloropropanoic acid > $3$-chloropropanoic acid > propanoic acid
• B. $3$-chloropropanoic acid > $2$-chloropropanoic acid > $2,2$-dichloroacetic acid > propanoic acid
• C. $2,2$-dichloroacetic acid > $3$-chloropropanoic acid > $2$-chloropropanoic acid > propanoic acid
• D. $2,2$-dichloroacetic acid > propanoic acid > $2$-chloropropanoic acid > $3$-chloropropanoic acid

Answer 1

Answer: (A)

Acidic strength $\propto \, K_a$ values Due to -I effect of electron withdrawing -Cl group, chloropropanoic acid is stronger acid than propanoic add. Further, greater the· number of electron withdrawing substituents; greater would· be the acidic strength. Inductive effect decreases rapidly with distance and so is the acidic strength. Hence he correct order of acidic strength (or $K_a$ values) will be·