Answer to Question #306741 in Organic Chemistry for Anne

Question

Compounds A and B was discovered by a group of scientists. Compound A is a dipeptide, optically inactive. While compound B is a tripeptide and optically active. Compound A is formed when compound C and compound D joined together by condensation reaction. Whereas monomers E and F are formed by modifying the compounds C and D. Polymer G is formed by the condensation reaction of monomers E and F.

Draw the possible structural formulae of compounds A, B, C, D, E, F and polymer G.

Label the peptide bond(s) for compounds A and B.

With the aid of diagram, discuss why compounds A and B are classified as an optically inactive compound and optically active compound, respectively?

Draw the possible structural formulae for repeating unit of polymer G.

How would you distinguish between polymer G and their repeating unit?

Answer 1

Peptides & Proteins1. The Peptide Bond

If the amine and carboxylic acid functional groups in amino acids join together to form amide bonds, a chain of amino acid units, called a peptide, is formed. A simple tetrapeptide structure is shown in the following diagram. By convention, the amino acid component retaining a free amine group is drawn at the left end (the N-terminus) of the peptide chain, and the amino acid retaining a free carboxylic acid is drawn on the right (the C-terminus). As expected, the free amine and carboxylic acid functions on a peptide chain form a zwitterionic structure at their isoelectric pH.

By clicking the "Grow Peptide" button, an animation showing the assembly of this peptide will be displayed. The "Show Structure" button displays some bond angles and lengths that are characteristic of these compounds.