Biochemistry—Peptide Bond Resonance Resonance structures drawn for the peptide bond imply which of the following?

Introduction / Context:
Peptide bond resonance is central to protein structure. Delocalization between the carbonyl and the amide nitrogen creates partial double-bond character and defines peptide planarity.

Given Data / Assumptions:

• Resonance implies electron delocalization between C=O and C–N.
• Partial double-bond character shortens and strengthens C–N relative to a single bond.
• Restricted rotation yields a planar peptide unit.

Concept / Approach:
If resonance increases bond order above 1, the bond becomes stronger and less rotatable. Therefore both strengthening and partial double-bond character are correct.

Step-by-Step Solution:

Verification / Alternative check:
Empirical peptide C–N bond lengths fall between typical single and double bonds, consistent with partial double-bond character.

Why Other Options Are Wrong:

• D is incorrect; peptide bond electronic structure is well characterized.
• E is incorrect; free rotation contradicts resonance-imposed planarity.

Common Pitfalls:
Assuming resonance only affects stability but not geometry; confusing φ/ψ mobility with peptide ω rigidity.

Final Answer:
Both A and B.