Q.α - Amino acids have high melting points compared to the corresponding amines or carboxylic acids of comparable molecular mass.

Step 1. An ordinary simple amine or carboxylic acid of comparable molecular mass is held together as a solid crystal only by relatively weak intermolecular forces -- hydrogen bonding and dipole-dipole/van der Waals attractions between neutral covalent molecules.

Step 2. An alpha-amino acid, by contrast, does not exist as a simple neutral covalent molecule at all: internal proton transfer from its acidic -COOH group to its basic -NH2 group converts it into a dipolar salt, the zwitter ion (-COO- and -NH3+ coexisting in the same molecule, net charge zero -- section 14.3.1, Fig. 14.15).

Step 3. In the solid state, these zwitterionic amino-acid molecules pack together into a crystal lattice held by strong ELECTROSTATIC (ionic) forces between the -COO- and -NH3+ groups of neighbouring molecules -- essentially the same kind of strong ionic lattice force that holds together an ordinary inorganic salt crystal, rather than the much weaker molecular forces of a simple covalent solid. …

Contrast the zwitterionic, salt-like solid-state structure of amino acids (strong ionic lattice forces) with the simple covalent molecular structure of amines/carboxylic acids ( …

• Attributing the high melting point simply to 'more hydrogen bonding' rather than to the fundamentally different, IONIC (zwitterionic/salt-like) nature of the solid. …