Solution: In a random (amino acid sequence) polypeptide chain, rotation is severely restricted about the following bonds:A. Bond from backbone α-C to α-NH2 or to α-COOH groupsB. Peptide bondC. Backbone α-C to theside chain carbonsD. Terminal α-NH2 to α-COOH groupsE. None of the above

Problem

In a random (amino acid sequence) polypeptide chain, rotation is severely restricted about the following bonds:

A. Bond from backbone α-C to α-NH2 or to α-COOH groups

B. Peptide bond

C. Backbone α-C to theside chain carbons

D. Terminal α-NH2 to α-COOH groups

E. None of the above

Solution

Generally, the covalent bonds in a molecule gives freedom for rotation of substituents linked by them. This will only be restricted by connections involving pi bonds, as these bonds share the p orbitals with each other and its rotation would require a 180º twist of the shared orbitals, which would either require a lot of energy and would eventually break the π bond.

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