Question

Rank the following compounds in order of decreasing acid strength (most acidic $\to$ least acidic).

• A. $2>4>1>3$
• B. $1>3>4>2$
• C. $3>1>2>4$
• D. $3>1>4>2$

Answer 1

Answer: (D)

$3>1>4>2$

After the removal of proton $-O-$ group is formed which is stabilized by resonance in $1,3$ and $4$, whereas $2$ doesn't have such stabilizing factor. Hence, $2$ will be least acidic. Further, presence of electron withdrawing group and its stronger effect stabilizes the phenoxide more. Since, presence of $-N{O}_2$ group in para position causes more electron-withdrawing effect than that in meta position, $1$ will be less acidic than $3$.
Hence, the order of acid strength is $3>1>4>2$