Proteins are linear polymers of amino acids linked together by peptide bonds . A peptide bond (–CO–NH–) exhibits resonance, where the lone pair of electrons on the nitrogen atom is delocalised into the carbonyl group . This resonance gives the C–N bond partial double bond character . According to the principles of chemical bonding, bond lengths in resonance hybrids are intermediate between single and double bonds . Specifically, as bond order increases, bond length decreases . In the sources, a typical C–N single bond length is 143 pm, while a C=N double bond is 138 \pm . Due to its partial double bond character, the C–N bond in a peptide is shorter (typically around 132 pm) than a standard C–N single bond . Therefore, the statement that the bond is longer is incorrect. Additionally, this resonance restricts rotation about the bond, resulting in a planar geometry for the peptide group .