b
$\begin{array}{*{20}{c}}
{Cl - C{H_2} - \mathop C\limits^* H - C{H_2} - C{H_3},} \\
{|\,\,\,\,\,\,\,\,\,\,\,} \\
{C{H_3}\,\,\,\,\,\,}
\end{array}\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,Cl} \\
{\,\,\,\,\,\,\,|} \\
{C{H_3} - CH - \mathop C\limits_* H - C{H_3}} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{C{H_3}\,\,\,\,\,\,\,\,\,\,\,}
\end{array}$