I am not familiar with the abbreviation IEP. Would you please define it for me? The side chain (-CH3) of alanine is non-polar compared with some of the other side chains, such as -CH2OH, the side chain of serine. There is a very big difference, however, in how an alanyl residue in a polypeptide behaves versus the free amino acid alanine. What intermolecular force (IMF) is present in free alanine but not in an alanyl residue?