1) Isoprene:

\[\begin{array}{cc}\ce{H2C = C – C = CH2}\\
|\phantom{….}|\\\ce{\underset{\text{(isoprene)}}{CH3  H}}\end{array}\]

2) Polymer of isoprene (polyisoprene or natural rubber):

\[\begin{bmatrix}\begin{array}{cc}\ce{H\phantom{…………}}\ce{H}\\
|\phantom{………….}|\\\ce{- C – C = C – C -}\\
|\phantom{…..}|\phantom{….}|\phantom{….}|\\
\ce{H\phantom{…}} \ce{CH3\phantom{..}} \ce{H\phantom{…}} \ce{H}\end{array}\end{bmatrix}_\text{n}\]

(polyisoprene/rubber)