\documentclass{ppex}
\nonstopmode
\AtBeginDocument {\setlength \unitlength {0.09pt}}
\usepackage {epic,hetarom}
\pagestyle{empty}

\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {epic,hetarom}
\threehetero      {1==S}     {3Sa==H$_3$C;3Sb==H$_3$C}
\fourhetero       {1==O;2==O}{4Sa==COOH;4Sb==COOH}
\fiveheterov[eb]  {1==N}     {1D==O;4SA==MeO;4SB==OMe;5==Cl;6==Cl}
\sixheterov [c]   {1==N}     {1==Cl;4==F;2==CH$_3$}
\end{document}
