[pixie]

The melting point of CH3CH(NH2)COOH is 297 deg C while that of CH3CH(OH)COOH is18 deg C. Can someone please exlain why these melting points are so different?

[GSR]

electronegativity of nitrogen make amines polar molecules. Just being polar molecules will cause amines to have higher melting points and boiling points and be more soluble in water than similar sized nonpolar molecules

the intermolecular bonds between amines are hydrogen bonds rather than dipole-dipole bonds.  They are the attraction between the hydrogen of one molecule and the nitrogen of another molecule. Some people look at the hydrogen atom in a hydrogen bond as being a bridge between two nitrogen atoms. The hydrogen bonding of amines increases their melting points, boiling points and solubility in water even more.

[pixie]

but what about the OH group in the CH3CH(OH)COOH isnt that very polar too so it will form hydrogen bonds with itself no? making it stronger too? Why is the melting point so low then?

[movies]

Are you familiar with Zwitterions?

[GSR]

In terms of acid-base theory, 2-aminopropanoic acid exists in the Zwitterionic form , and not in the alternative form see the images.

NH2 is a stronger base than –CO2- and

-COOH is a stronger acid than NH3+. Thus the equilibrium lie on the right(NH3+).

The high melting point of (Zwitterionic form) is evidence for its ionic structure.

its not the case with alcohol.

[movies]

Yup.