Question

Arrange the following compounds in order of their increasing acid strength. 

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

Hint:

In dicarboxylic acids:
Closer COOH groups increase acidity
Oxalic acid type (adjacent COOH) is strongest
Longer chains reduce \(-I\) effect

Answer 1

The Correct Option is C

Concept: Acid strength in dicarboxylic acids depends on:

• Electron withdrawing effect of second COOH group
• Distance between the two COOH groups

Closer COOH groups ⇒ stronger -I effect ⇒ stronger acid.

Step 1: Identify structures

• I = Longest chain between COOH groups ⇒ weakest
• IV = Slightly shorter chain
• II = Even closer COOH groups
• III = Two COOH directly attached (oxalic-type) ⇒ strongest

Step 2: Apply inductive effect rule

Greater proximity of COOH groups increases acidity. Thus:
\[ \text{I} < \text{IV} < \text{II} < \text{III} \]