a
\(\begin{array}{*{20}{c}}
{\mathop C\limits^1 {H_3} - \mathop C\limits^2 - \mathop C\limits^3 H - \mathop C\limits^4 {H_3}} \\
{\,\,\,||{\mkern 1mu} {\mkern 1mu} \,\,\,\,\,\,{\mkern 1mu} {\mkern 1mu} |\,\,\,\,\,\,\,\,{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} } \\
{{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} O{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,C{H_3}\,\,\,{\mkern 1mu} {\mkern 1mu} }
\end{array}\) \( 3-\) Methyl \(-2-\) butanone