The presence of chlorine atoms on the carbon next to the carboxyl group, as in chloroethanoic acid, makes the acid stronger because chlorine
Correct answer: C. withdraws electron density, spreading and stabilising the negative charge of the anion
- A. donates electrons to the carboxyl group
- B. increases the molar mass
- C. withdraws electron density, spreading and stabilising the negative charge of the anion
- D. makes the molecule non polar
Explanation
The electron withdrawing inductive effect of chlorine pulls charge away from the carboxylate oxygens, so the ion is more stable and the acid ionises more readily, and trichloroethanoic acid is stronger still because three chlorines act together. The effect weakens rapidly with distance along the chain. Electron releasing alkyl groups have the opposite effect, which is why ethanoic acid is weaker than methanoic acid.
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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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