\documentclass{ppex}
\nonstopmode
\AtBeginDocument {\setlength \unitlength {0.09pt}}
\usepackage {aliphat}
\pagestyle{empty}
\setlength\textwidth{207.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {aliphat}
\setlength\unitlength{0.1pt}
\tetrastereo{1==F;%
   2==Cl;3==H;4==Br}
\dtetrastereo{1==F;%
   2==Cl;3==H;4==Br}
\ethanestereo{1==C;2==C}
  {1==F;2==Cl;3==H;4==Br;%
   5==Ph;6==H}
\end{document}