$\mathop {{C_2}{H_5}OH}\limits_{\left( I \right)} $ $\mathop {{C_2}{H_5}Cl}\limits_{\left( {II} \right)} $ $\mathop {{C_2}{H_5}C{H_3}}\limits_{\left( {III} \right)} $ $\mathop {{C_2}{H_5}OC{H_3}}\limits_{\left( {IV} \right)} $
$\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||} \\
{C{H_2} = CH - C{H_2} - C - H}
\end{array} \to C{H_3} - C{H_2} - C{H_2} - C{H_2}OH$