Monomer of natural rubber: which compound polymerises to form natural rubber?

Introduction / Context:
Natural rubber is a polyterpene formed in plants via enzymatic polymerisation. Identifying its monomer clarifies its structure and properties.

Given Data / Assumptions:

• Natural rubber is cis-1,4-polyisoprene.
• Isoprene = 2-methyl-1,3-butadiene.
• Butyl rubber, by contrast, is based on isobutylene copolymerised with isoprene in small amounts.

Concept / Approach:
The repeating unit in natural rubber arises from isoprene via 1,4-addition polymerisation, yielding an unsaturated backbone responsible for vulcanisation behaviour.

Step-by-Step Solution:
Identify isoprene as the terpenic monomer.Exclude isobutylene which forms butyl rubber with different properties.Exclude DMT which is a polyester intermediate for PET.

Verification / Alternative check:
Structural analyses show cis-1,4 double-bond configuration in natural rubber.

Why Other Options Are Wrong:
DMT relates to PET; isobutylene is not the sole monomer of natural rubber.

Common Pitfalls:
Confusing isoprene with isobutylene due to similar names.

Final Answer:
Isoprene