What are the N terminus and C terminus of a peptide chain?

In a peptide chain, the N terminus and C terminus refer to the two ends of the molecule, which are defined by their specific chemical groups.

• N terminus: This is the end of the peptide chain that features a free $\alpha$-amino group (–NH${}_2$). By convention, when writing the structure of a peptide, the N terminus is placed on the left side.1
• C terminus: This is the end of the peptide chain that features a free carboxyl group (–COOH). By convention, the C terminus is placed on the right side of the structure.1

These termini represent the ends of the polypeptide chain where the amino and carboxyl groups have not been consumed by the formation of a peptide bond, which otherwise links the individual amino acid residues together.1