Question

Which polymer has ‘chiral’ monomer(s)?
A. PHBV
B. Nylon 6,6
C. Buna-N
D. Neoprene

Answer 1

Hint: The term ‘chiral’ is used to describe the object that is non-superimposable on its mirror image. And polymer is a substance or a material composed of many repeating subunits called monomers. For checking chirality in your compound, the presence of chiral center or chiral carbon is very important.

Complete step-by-step answer:
In a chiral molecule, there is a chiral center. Chiral centers are tetrahedral atoms, mostly carbons, that have four different substituents.
In the given question, there are four polymers which are PHBV; Nylon 6,6; Buna-N; Neoprene. The structures of these polymers are as follows,
1.PHBV: \[{\left( { - O - CHC{H_3} - C{H_2} - CO - O - CH{C_2}{H_5} - C{H_2} - CO - } \right)_n}\]
2.Nylon 6,6: \[{\left[ { - CO{{\left( {C{H_2}} \right)}_4}CO - NH{{\left( {C{H_2}} \right)}_6}NH - } \right]_n}\]
3.Buna-N: \[{\left[ { - C{H_2} - CH = CH - C{H_2} - CH\left( {CN} \right) - C{H_2} - } \right]_n}\]
4.Neoprene: \[{\left( { - C{H_2} - CH = CCl - C{H_2} - } \right)_n}\]
The monomers that are the subunits of the above polymers are as follows,
1.PHBV: \[C{H_3} - CHOH - C{H_2} - COOH\] which is called 3-hydroxybutanoic acid and \[C{H_3} - C{H_2} - CHOH - C{H_2} - COOH\] which is called 3-hydroxypentanoic acid are the two monomers of PHBV.
2.Nylon 6,6: \[H{O_2}C - {\left( {C{H_2}} \right)_4} - C{O_2}H\] which is called adipic acid and \[{H_2}N - {\left( {C{H_2}} \right)_6} - N{H_2}\]which is called hexamethylenediamine are the two polymers of Nylon 6,6.
3.Buna-N: \[C{H_2} = CH - CH = C{H_2}\] which is called 1,3-butadiene and \[C{H_2}\left( {CN} \right) = C{H_2}\]which is called acrylonitrile are the two polymers of Buna-N.
4.Neoprene: \[C{H_2} = CH - CCl = C{H_2}\] which is called chloroprene is the polymer of Neoprene.
From the above-mentioned monomers, we can see that only in PHBV, also known as Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), both the monomers are chiral compounds.
In both the monomers of PHBV, the chiral center or the chiral carbon has four different substituents. In 3-hydroxybutanoic acid, the third carbon has these four different groups: \[ - OH\], \[ - C{H_3}\], \[ - H\], \[ - C{H_2} - COOH\]. In 3-hydroxypentanoic acid, the third carbon has these four different groups: \[ - OH\], \[ - C{H_2} - C{H_3}\], \[ - C{H_2} - COOH\], \[ - H\]. Hence, both these monomers are chiral.

Therefore, the correct answer is option A that is PHBV.

Note: A chiral molecule is non-superimposable on its mirror image, so that the mirror image is actually a different molecule. The two non-identical mirror images are known as the pair of enantiomers.