\(\begin{align} & C{{H}_{3}}\,-\,\,C{{H}_{2}}\,-\,C\equiv \overset{-}{\mathop{C}}\,\overset{+}{\mathop{N}}\,a\,\,\xrightarrow{C{{H}_{3}}\,-\,\,C{{H}_{2}}\,-\,\,C{{H}_{2}}\,-\,\,C{{H}_{2}}\,-\,\,Br} \\
& C{{H}_{3}}\,-\,\,C{{H}_{2}}\,-\,\underset{3\,\,-\,\,octyne}{\mathop{C{{H}_{2}}\,-\,\,C{{H}_{2}}\,-\,\,C}}\,\equiv C\,-\,\,C{{H}_{2}}\,\,-\,\,C{{H}_{3}} \\
\end{align}\)



${H_2}C\, - \,\,\mathop C\limits_{\mathop |\limits_D } H\, - \,\,\mathop C\limits_{\mathop |\limits_{C{H_3}} } H\, - \,\,C{H_3}\, + \,\,Br\,\, \to \,\,'X'\,\, + \,\,HBr$