Isoprene ($\mathrm{C}{\mathrm{H}}_2=\mathrm{C}(\mathrm{C}{\mathrm{H}}_3)\mathrm{CH}=\mathrm{C}{\mathrm{H}}_2$)

Isoprene is 2-methylbuta-1,3-diene, ${\mathrm{C}}_5{\mathrm{H}}_8$. Its two carbon-carbon double bonds form a conjugated system.

Polymerization of isoprene can generate different chain geometries. The configuration and connectivity of the repeating units influence the properties of the resulting polymer, so monomer identity alone does not completely specify a rubber-like material.