$\begin{array}{*{20}{c}}
{^{C{H_3}}} \\
{_H}
\end{array}\begin{array}{*{20}{c}}
{{\text{ }}\backslash {\text{ }}} \\
/
\end{array}\mathop C\limits^{} {\mkern 1mu} = \mathop C\limits^{} {\mkern 1mu} \begin{array}{*{20}{c}}
/ \\
{{\text{ }}\backslash {\text{ }}}
\end{array}_{\mathop C\limits^{} {\kern 1pt} \equiv \mathop C\limits^{} {\kern 1pt} - \mathop C\limits^{} {\kern 1pt} {H_2}\mathop C\limits^{} {\kern 1pt} {H_3}}^H{\mkern 1mu} $
$\begin{array}{*{20}{c}}
{R = - CH - Cl}\\
{|\,\,}\\
{\,\,\,\,C{H_3}}
\end{array}\,\,\,\,,\,\,\,\,\,\,\,\,\,\,\begin{array}{*{20}{c}}
{S = - CH - Cl}\\
{|\,\,}\\
{Br}
\end{array}$