\documentclass{ppex}
\nonstopmode
\AtBeginDocument {\setlength \unitlength {0.09pt}}
\usepackage {aliphat}
\pagestyle{empty}
\setlength\textwidth{207.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {aliphat}
\ethylene{1==C;2==C}
    {1==F;2==Cl;3==H;4==Br}
\qquad
\ethylenev[t{2+}]{1==C;2==N}
    {1==H$_3$C;2==CH$_3$;3==H}
\end{document}