b
$(b)$ $\underset{(Hoffmann\,bromamide\,reaction)}{\mathop{\begin{matrix}
OH\,\,\,\,\,\,\,\,O\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
|\,\,\,\,\,\,\,\,\,\,\,\,\,\,||\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
Ph-CH-C-N{{H}_{2}}\xrightarrow[KOH]{B{{r}_{2}}} \\
\end{matrix}}}\,\underset{(unstable)}{\mathop{\begin{matrix}
OH\,\,\,\,\,\,\,\,\,\, \\
|\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
Ph-CH-N{{H}_{2}}\to \\
\end{matrix}}}\,\begin{matrix}
O \\
|| \\
Ph-C-H \\
\end{matrix}$