Why does a carboxylic acid have a much higher boiling point than an alcohol of similar mass?
Carboxylic acids form especially strong hydrogen bonds — in fact two molecules pair up into a cyclic 'dimer' held by two hydrogen bonds, effectively doubling the particle size.
Carboxylic acids form especially strong hydrogen bonds — in fact two molecules pair up into a cyclic 'dimer' held by two hydrogen bonds, effectively doubling the particle size. Breaking those extra bonds needs more energy, so the boiling point is higher than an alcohol of comparable molar mass, which forms only single hydrogen bonds. It's the dimerisation that pushes the boiling point up.
Key point
Carboxylic acids form hydrogen-bonded dimers, raising the boiling point above a similar alcohol.
Common mistake
assuming similar molar mass means a similar boiling point.
Memory tip
acids pair into dimers (two H-bonds) → extra-high boiling point.
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