The correct order of decreasing acidity of the following aliphatic acids is:

Question

Question

This question was previously asked in

NEET 2025 Official Paper (Held On: 04 May, 2025)

Answer 1

CONCEPT:

Acidity of Aliphatic Carboxylic Acids

The acidity of carboxylic acids is influenced by the nature of the substituents attached to the carbon chain.
Electron-withdrawing groups increase acidity by stabilizing the conjugate base (carboxylate ion), while electron-donating groups decrease acidity by destabilizing the conjugate base.
Formic acid (HCOOH) is the most acidic among simple aliphatic carboxylic acids because it has no alkyl groups, which are electron-donating by nature.
As the size of the alkyl group increases, the electron-donating inductive effect (-I effect) becomes stronger, making the acid weaker.

EXPLANATION:

HCOOH (formic acid): No alkyl group, highest acidity.
CH₃COOH (acetic acid): One methyl group (-CH₃), moderately acidic. (+I)
(CH₃)₂CHCOOH (isobutyric acid): Two methyl groups attached to the same carbon, further decreases acidity. ( two +I)
(CH₃)₃CCOOH (pivalic acid): Three methyl groups attached to the same carbon, lowest acidity due to strong electron-donating effect. (three +I)
The correct order of decreasing acidity is:
HCOOH > CH₃COOH > (CH₃)₂CHCOOH > (CH₃)₃CCOOH

Therefore, the correct answer is Option 3: HCOOH > CH₃COOH > (CH₃)₂CHCOOH > (CH₃)₃CCOOH.