Carboxylic acids have higher boiling points due to more extensive intermolecular hydrogen bonding. These bonds persist even in the vapour phase, with most carboxylic acids existing as dimers in the vapour phase or in aprotic solvents.
Why do carboxylic acids exhibit higher boiling points compared to aldehydes, ketones, and alcohols of similar molecular masses?
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Carboxylic acids generally have higher boiling points than aldehydes, ketones, and alcohols of similar molecular masses due to the presence of strong hydrogen bonding in carboxylic acids. Carboxylic acids contain both hydrogen bond acceptor (carbonyl oxygen) and donor (hydroxyl hydrogen) sites, facilitating the formation of intermolecular hydrogen bonds. This enhances the forces holding carboxylic acid molecules together, requiring more energy to overcome and transition into the gaseous phase. In contrast, aldehydes and ketones lack the hydroxyl hydrogen, and alcohols, while having hydrogen bond donor sites, lack the strong hydrogen bond acceptor present in the carboxyl group.