a
\(\underset{(E)\,-2-hepten-4-yne}{\mathop{\begin{matrix}
   ^{\overset{1}{\mathop{C}}\,{{H}_{3}}}  \\
   _{H}  \\
\end{matrix}\begin{matrix}
   \text{ }\!\!\backslash\!\!\text{ }  \\
   /  \\
\end{matrix}\overset{2}{\mathop{C}}\,=\overset{3}{\mathop{C}}\,\begin{matrix}
   /  \\
   \text{ }\!\!\backslash\!\!\text{ }  \\
\end{matrix}_{\overset{4}{\mathop{C}}\,\equiv \overset{5}{\mathop{C}}\,-\overset{6}{\mathop{C}}\,{{H}_{2}}\overset{7}{\mathop{C}}\,{{H}_{3}}}^{H}}}\,\)