What conformational preference is primarily attributed to steric hindrance from amino acid side chains?

The trans conformation is primarily favored in peptide bonds due to steric hindrance from the amino acid side chains. In a trans configuration, the two alpha-carbons that flanking the peptide bond are positioned on opposite sides of the bond. This orientation minimizes steric clashes between the bulky side chains of the amino acids, reducing repulsion and allowing for a more stable conformation.

When considering the cis configuration, the side chains of the adjacent amino acids are positioned on the same side of the peptide bond. This proximity can lead to significant steric hindrance and conflict between side chains, particularly when they are large or bulky. Although cis peptide bonds can occur, they are generally less favorable energetically and are found in specific contexts, such as in proline residues.

The linear and circular options are not relevant to the conformational preference of peptide bonds. Peptides adopt a linear structure by default, and circular peptides occur in special cases but are not defined by steric hindrance related to amino acid side chains. Thus, the trans form remains the preferred conformation in typical polypeptide chains due to the minimization of steric hindrance.