Select the correct order of the acids strength?
Correct answer: B. CHCl2COOH > CH2ClCOOH > CH3COOH
- A. CH3COOH >> CHCl2COOH > CH2ClCOOH
- B. CHCl2COOH > CH2ClCOOH > CH3COOH
- C. CH3COOH > CHCl2COOH > CH2ClCOOH
- D. CHCl2COOH >> CH2COOH > CH2ClCOOH
Explanation
The acidity of carboxylic acids is influenced by the presence of electron-withdrawing groups. These groups stabilize the carboxylate ion by delocalizing the negative charge via inductive effects, thereby increasing acidity. In the given options, CHCl2COOH is the strongest acid because it has two chlorine atoms, which significantly withdraw electrons, enhancing the acid strength. CH2ClCOOH, with one chlorine, is less acidic than CHCl2COOH but more acidic than CH3COOH, which lacks electron-withdrawing groups and is thus the weakest acid. Option B correctly identifies this trend, while the other options incorrectly order the acids or introduce non-existent compounds.
This question appeared on the ETEA MDCAT 2016 paper, which you can sit online with every answer explained.
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About Reactivity of Carboxylic Acids
Carboxylic acids show acidic behaviour because their carboxylate ions are resonance-stabilised, and electron-withdrawing groups can change their strength. Reactions include neutralisation, esterification, formation of acid chlorides and amides, reduction, decarboxylation and substitution at the acyl carbon, which differs from the reactions of phenols.
Practise Carboxylic Acids
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