Question

The correct order of acidity for the following compounds is

• A. $I > II > III > IV$
• B. $III > I > II > IV$
• C. $III > IV > II > I$
• D. $I > III > IV > II$

Answer 1

Answer: (A)

$I > II > III > IV$

Answer 2

Due to ortho-effect, $(I)$ and $(II)$ are stronger acid than $(III)$ and $(IV)$. Due to two ortho hydroxyl groups in $(I)$, it is stronger acid than $(II). (Ill)$ is a stronger acid than $(IV)$ because at m-position, $-OH$ group cannot exert its $+R$ effect but can only exert its $-I$ effect while at $p-$ position, $-OH$ group exerts its strong $+R$ effect. Thus, the correct order of acidity is $: I > II > III > IV$.