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Question
Why are carboxylic acids more acidic than alcohols or phenols although all of them have hydrogen atom attached to an oxygen atom (—O—H)?
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Solution
- Carboxylic acids are more acidic than alcohols or phenols, although all of them have an −OH bond. This can be explained based on the stability of the conjugate base obtained after the removal of H+ from acids, phenols and alcohols.
- When hydrogen is removed from a carboxylic acid, the conjugate base formed is stable due to the equivalent resonating structures
- On the other hand, when hydrogen is removed from phenol, the conjugate base formed has more resonating structures than carboxylic acid but not equivalent resonating structures.
- Hence, the phenoxide ion is less stable than the carboxylate ion. So, phenol is less acidic than a carboxylic acid.
- Alcohols will be the least acidic among the given compounds because its conjugate base will be the least stable due to the absence of delocalisation of negative charge. Moreover, it will be destabilised by the +I effect of the alkyl group present in alcohols.
- Hence, the dissociation of O−H bonds in carboxylic acids are more favourable than that in phenols and alcohols.
- Carboxylic acids are more acidic than alcohols or phenols, although all of them have an −OH bond. This can be explained based on the stability of the conjugate base obtained after the removal of H+ from acids, phenols and alcohols.
- When hydrogen is removed from a carboxylic acid, the conjugate base formed is stable due to the equivalent resonating structures
- On the other hand, when hydrogen is removed from phenol, the conjugate base formed has more resonating structures than carboxylic acid but not equivalent resonating structures.
- Hence, the phenoxide ion is less stable than the carboxylate ion. So, phenol is less acidic than a carboxylic acid.
- Alcohols will be the least acidic among the given compounds because its conjugate base will be the least stable due to the absence of delocalisation of negative charge. Moreover, it will be destabilised by the +I effect of the alkyl group present in alcohols.
- Hence, the dissociation of O−H bonds in carboxylic acids are more favourable than that in phenols and alcohols.
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