Question

Arrange increasing order of acidic strength of following dicarboxylic acid.
(i) Oxalic acid
(ii) Succinic acid
(iii) Malonic acid
(iv) Adipic acid

• A. iii < ii < i < iv
• B. i < ii < iii < iv
• C. iv < iii < ii < i
• D. iv < ii < iii < i

Answer 1

The correct option is D iv < ii < iii < i

The dicarboxylic acids are stronger than monocarboxylic acid becasue it has a electron withdrawing ($-COOH$) group.
The increase in the $C{H}_2$ group in the compound will decrease the acidic strength of the compound because $C{H}_2$ is an +I effect group so it will increase the electron density on conjugate base.


Here, oxalic acid doesn't have +I group so it more acidic.
Then, malonic acid has one $C{H}_2$ and succinic acid has 2 $C{H}_2$ and adipic acid has 4 $C{H}_2$.
Therfore the strength of acid follows the order,
$Adipicacid<Succinicacid<Malonicacid<Oxalicacid$