Q.Why do amino acids generally have much higher melting points than simple carboxylic acids or amines of a similar molar mass, and why are they readily soluble in water?
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Start your 14-day free trial to unlock the full solution →Amino acids predominantly exist as zwitterions -- dipolar ions carrying a negatively charged carboxylate group, , and a positively charged ammonium group, , on the same molecule -- rather than as simple neutral molecules.
In the solid state, these charged groups on neighbouring amino acid molecules attract one another strongly, in much the same way as the ions in an ordinary ionic salt (such as sodium chloride) attract one another. This strong, ionic-type attraction holds the crystal lattice together far more tightly than the weaker intermolecular forces (such as ordinary hydrogen bonding or van der Waals forces) found in a simple carboxylic acid or amine of similar size, which is why amino acids need considerably more thermal energy to melt, and so have much higher melting points. …
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