NEET 2025 · ChemistryAcid acidityPrevious Year Question
The correct order of decreasing acidity of the following aliphatic acids is
- A.(A) \ce{HCOOH > CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH}✓
- B.(B) \ce{HCOOH > (CH3)3CCOOH > (CH3)2CHCOOH > CH3COOH}
- C.(C) \ce{(CH3)3CCOOH > (CH3)2CHCOOH > CH3COOH > HCOOH}
- D.(D) \ce{CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH > HCOOH}
Correct Answer
(A) (A) \ce{HCOOH > CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH}
Solution & Explanation
\textbf{Answer:} (A) \ce{HCOOH > CH3COOH > (CH3)2CHCOOH > (CH3)3CCOOH}. \textbf{Solution:} Electron-donating ($+I$) alkyl groups destabilise the carboxylate anion and reduce acidity. As more or larger alkyl groups are attached near the \ce{-COOH}, the $+I$ effect grows and acid strength falls. With no alkyl group, \ce{HCOOH} is the strongest; acidity then decreases through \ce{CH3COOH} and \ce{(CH3)2CHCOOH} to the weakest \ce{(CH3)3CCOOH}.
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