Some molecules contain both an amine and a carboxyl group, the amino acids. Polyamino acids are linked by amide bonds. Amide bonds are known as peptide bonds in peptides and enzymes. The nitrogen atom of an amine may have one, two, or three carbon groups attached to give primary amines, secondary amines, and tertiary amines, respectively. Carboxylic acids are readily converted to an amide by reaction of the corresponding acid chloride or ester with ammonia or an amine. Phthalimide is an imide derived from phthalic acid. Both an amine and a carboxylic acid are mono-functional compounds. The amine unnit reacts with the carboxylic acid under neutral conditions to give a zwitterion product, 2-ammoniopropanoate. Both the amine and the carboxyl of an amino acid undergo chemical reactions that are expected for each group.