Concept Explanation: Monomeric Unit of Natural Rubber

Natural rubber is a polymer, which means it is made up of many repeating smaller molecules called monomers. The monomeric unit is the fundamental building block that repeats to form the polymer chain.

Step 1: Understand Natural Rubber

Natural rubber is obtained from the latex of the rubber tree (Hevea brasiliensis). It is a natural polymer known for its elasticity and resilience.

Step 2: Identify the Monomer

The monomeric unit of natural rubber is isoprene. Chemically, isoprene is 2-methyl-1,3-butadiene, with the formula:

$C_5{H}_8$

Its structure is: $\mathrm{CH}2=C\left(\mathrm{CH}3\right)-\mathrm{CH}=\mathrm{CH}2$

Step 3: Polymerization Process

Isoprene monomers undergo addition polymerization to form polyisoprene, which is natural rubber. The polymerization can be represented as:

$n\mathrm{CH}2=C\left(\mathrm{CH}3\right)-\mathrm{CH}=\mathrm{CH}2\to [-\mathrm{CH}2-C(\mathrm{CH}3)=\mathrm{CH}-\mathrm{CH}2-]n$

Step 4: Evaluate the Options

• Styrene: Monomer for polystyrene, not natural rubber.
• Vinyl chloride: Monomer for PVC, not natural rubber.
• Isoprene: Correct monomer for natural rubber.
• Chloroprene: Monomer for neoprene (synthetic rubber), not natural rubber.

Final Answer

The monomeric unit of natural rubber is Isoprene.

Related Topics

• Polymers and Polymerization
• Natural vs Synthetic Rubbers
• Structure of Isoprene and Its Polymers
• Properties and Uses of Natural Rubber

Formulae and Theory

Chemical Formula of Isoprene: $C_5{H}_8$

Polymerization Reaction: n Isoprene → Polyisoprene (Natural Rubber)

Key Theory: Natural rubber is cis-1,4-polyisoprene. The cis configuration of the double bonds in the polymer chain gives rubber its elastic properties.