12. ORGANIC CHEMISTRY SOME BASIC PRINCIPLES AND TECHNIQUES (HM)
Explanation:
$\mathop {\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\
{C{H_3}C{H_2} - CH - CH - C{H_2}C{H_3}} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{\,\,\,\,\,\,C{H_2}\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{\,\,\,\,\,\,\,C{H_3}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}}\limits_{3 - ethyl - 4 - methyl\,hexane} $