The structure of Neoprene is :

Solution

Chemistry ma’am · 3 steps

Neoprene is chloroprene joined end to end, so look for a Cl on the double bond of a four-carbon unit.

1. Know the monomer. Neoprene is made from chloroprene, which is 2-chloro-1,3-butadiene, CH₂=C(Cl)-CH=CH₂. It is a diene with a Cl on carbon 2.
2. 1,4-addition. In free-radical polymerisation the two end carbons (C1 and C4) bond to the neighbouring units. The double bond shifts to the middle, between C2 and C3. So every repeat unit keeps one C=C, with the Cl sitting on that double bond.

   n CH₂=C(Cl)-CH=CH₂ → [-CH₂-C(Cl)=CH-CH₂-]ₙ

   Option	Repeat unit has	Polymer
   (a)	four carbons, one C=C, Cl on C2	Neoprene (from chloroprene)
   (b)	butadiene unit plus a CH₂-CH(CN) unit	Buna-N (butadiene + acrylonitrile)
   (c)	CH₂-CH(CN) only	Polyacrylonitrile (Orlon)
   (d)	triazine ring linked by NH-CH₂	Melamine-formaldehyde resin

3. So. Only (a) is the chloroprene repeat unit, so (a) is the structure of neoprene.

The idea to keep. For a rubber made from a 1,3-diene, the repeat unit is four carbons with the double bond moved to the middle. Name the monomer first, then match the substituent: Cl means neoprene, CN means Buna-N.

Answer from the NTA final answer key. Solution by PrepWiser.