Final answer:
Steric constraints on phi and psi angles can lead to forbidden conformations due to steric clashes between atoms. These conformations are energetically unfavorable and less commonly observed in stable molecules or peptides.
Step-by-step explanation:
Steric constraints refer to the hindrance or restriction of molecular movement due to the presence of bulky substituents or groups. In terms of phi and psi angles in organic molecules or peptides, there are certain combinations of values that are considered to be forbidden conformations because they lead to steric clashes or unfavorable interactions between atoms. This means that these combinations of phi and psi angles are energetically unfavorable and less commonly observed in stable molecules or peptides.
For example, in a peptide chain, certain combinations of phi and psi angles can result in clashes between the side chains of amino acids, leading to strained or distorted conformations. These steric constraints help to determine the overall shape and stability of the peptide's structure.
Therefore, the statement that steric constraints on phi and psi give an example of forbidden conformations is true.