In this module:

Planarity of Peptide Bonds

Interestingly, peptide bonds have a second resonance form, as demonstrated below. This means that the peptide bond (the C=O and N-H) all reside in a single plane. Thus, there is no rotation around the bond.

Click on the structure below to switch the resonance forms of the peptide bond.

The structure at the right shows a peptide bond between the amino acids valine (Val) and serine (Ser). The amino acids are taken from the crystal structure of hemoglobin (αVal₁₃₂ and αSer₁₃₃). The four atoms that are part of the peptide bond are shown as larger spacefilling models. Because of the partial double bond between the α carbon and the amine nitrogen, no rotation is possible around that bond.