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ChemistryNEET 2025Carboxylic acids: acidity and reactions

Aldehydes, Ketones and Carboxylic Acids

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

  1. A.(CH3)3CCOOH>(CH3)2CHCOOH>CH3COOH>HCOOH\mathrm{(CH_3)_3CCOOH > (CH_3)_2CHCOOH > CH_3COOH > HCOOH}
  2. B.CH3COOH>(CH3)2CHCOOH>(CH3)3CCOOH>HCOOH\mathrm{CH_3COOH > (CH_3)_2CHCOOH > (CH_3)_3CCOOH > HCOOH}
  3. C.HCOOH>CH3COOH>(CH3)2CHCOOH>(CH3)3CCOOH\mathrm{HCOOH > CH_3COOH > (CH_3)_2CHCOOH > (CH_3)_3CCOOH}✓
  4. D.HCOOH>(CH3)3CCOOH>(CH3)2CHCOOH>CH3COOH\mathrm{HCOOH > (CH_3)_3CCOOH > (CH_3)_2CHCOOH > CH_3COOH}

Solution

Alkyl groups are electron-releasing and destabilise the carboxylate anion, so acidity falls as alkyl substitution grows: HCOOH>CH3COOH>(CH3)2CHCOOH>(CH3)3CCOOH\mathrm{HCOOH > CH_3COOH > (CH_3)_2CHCOOH > (CH_3)_3CCOOH}.

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