NEET 2025 — Chemistry solution

NEET2025Chemistry

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

A
(CH $_{3}$ ) $_{3}$ CCOOH > (CH $_{3}$ ) $_{2}$ CHCOOH > CH $_{3}$ COOH > HCOOH
B
CH $_{3}$ COOH > (CH $_{3}$ ) $_{2}$ CHCOOH > (CH $_{3}$ ) $_{3}$ CCOOH > HCOOH
C
HCOOH > CH $_{3}$ COOH > (CH $_{3}$ ) $_{2}$ CHCOOH > (CH $_{3}$ ) $_{3}$ CCOOH
D
HCOOH > (CH $_{3}$ ) $_{3}$ CCOOH > (CH $_{3}$ ) $_{2}$ CHCOOH > CH $_{3}$ COOH

Solution

Acidity is inversely related to the +I (electron-donating) effect of substituents near $-$ COOH. More alkyl groups donate electrons toward the carboxyl, destabilising the conjugate base and decreasing acidity.

HCOOH has no alkyl group → strongest acid.

CH $_{3}$ COOH has one methyl → next.

(CH $_{3}$ ) $_{2}$ CHCOOH has two methyls (isobutyric).

(CH $_{3}$ ) $_{3}$ CCOOH has three methyls (pivalic) → weakest of these.

$∴$ HCOOH > CH $_{3}$ COOH > (CH $_{3}$ ) $_{2}$ CHCOOH > (CH $_{3}$ ) $_{3}$ CCOOH.

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