In x-ray studies of crystalline peptides, Linus Pauling and Robert Corey found that the C-N bond in the peptide link is intermediate in length (1.32 Å) between a typical C-N single bond (1.49 Å) and a C=N double bond (1.27 Å). They also found that the peptide bond is planar (all four atoms attached to the C-N group are located in the same plane) and that the two a-carbon atoms attached to the C-N are always trans to each other (on opposite sides of the peptide bond).
What does the length of the C-N bond in the peptide linkage indicate about its strength (i.e., whether it is single, double, or triple)?
A The C-N peptide bond has similar strength to a C-N single bond.
B The C-N peptide bond is stronger than a C-N single bond.
C The C-N peptide bond is stronger than a CNN bond.
D The C-N peptide bond has similar strength to a C=N bond.