a
$C_6H_5Br + NaO - CH_2 - CH = CH_2$ $\longrightarrow$ $\begin{array}{l} {C_6}{H_5} - O - C{H_2} - CH = C{H_2} + NaBr\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\rm{Allyl\, phenyl\, ether}} \end{array}$