Asked in UHS MDCAT 2017 2017Moderate

Select the correct acidic strength order of chloro substituted acids:

Correct answer: C. Cl3CCOOH > Cl2CHCOOH > ClCH2COOH > CH3COOH

  • A. CH3COOH > ClCH2COOH > Cl2CHCOOH > Cl3CCOOH
  • B. CH3COOH > Cl2CHCOOH > Cl3CCOOH > ClCH2COOH
  • C. Cl3CCOOH > Cl2CHCOOH > ClCH2COOH > CH3COOH
  • D. Cl3CCOOH > CH3COOH > Cl2CHCOOH > ClCH2COOH

Explanation

Chlorine is an electronegative atom and it pulls the electron density towards itself thus spreading the charge and making the conjugate base stable. This leads to the carboxylic acid being more acidic. As the number of chlorines increases, the acidity increases too.

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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.

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