
$(i)$ $C{H_3}C{H_2}C{H_2}C{H_3}$
$(ii)$ $C{H_3} - CH = CH - C{H_3}$
$(iii)$ $C{H_2} = CH - CH = C{H_2}$
$(iv)$ $H - C \equiv C - H$


$\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,H\,\,\,\,\,{C_4}{H_9}} \\
{\,\,\,\,\,\,\,\,\,|\,\,\,\,\,\,\,\,\,|} \\
{C{H_3}C{H_2} - C - C - C{H_3}} \\
{\,\,\,\,\,\,\,\,|\,\,\,\,\,\,\,\,\,|} \\
{\,\,\,\,\,\,\,\,\,C{H_3}\,\,\,\,C{H_3}}
\end{array}$