Dimerisation of Carboxylic Acid via Hydrogen Bond

Carboxylic acids such as ethanoic acid (molecular mass 60.0) can form dimers via hydrogen bonds in vapour state or when dissolved in organic solvents.

230522 dimerisation via h bond

The polar portion of ethanoic acid is stabilised by a partner which is the driving force of dimerisation.

This results in the doubling of the molecular mass of ethanoic acid to 120.0.

The process of dimerisation takes place over a range of conditions such as temperature and pressure for vapour state.

This means the apparent molecular mass of a mixture of monomer and dimer can range from 60.0 to 120.0.

230522 range of Mr due to mixture

If apparent molecular mass is closer to 60.0, the extent of dimerisation is low and most of the species exist as monomers.

If apparent molecular mass is closer to 120.0, the extent of dimerisation is high and most of the species exist as dimers.

Topic: Intermolecular Forces, Physical Chemistry, A Level Chemistry, Singapore

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