$\begin{array}{*{20}{c}} {R = - CH - Cl}\\ {|\,\,}\\ {\,\,\,\,C{H_3}} \end{array}\,\,\,\,,\,\,\,\,\,\,\,\,\,\,\begin{array}{*{20}{c}} {S = - CH - Cl}\\ {|\,\,}\\ {Br} \end{array}$