\documentclass{ppex}
\nonstopmode
\usepackage {m-chemic}
\pagestyle{empty}
\setlength\textwidth{207.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {m-chemic}
\definechemical[sixring]
  {\chemical[SIX,B,R,RZ135]%
            [R_1,R_3,R_5]}
\startchemical[size=small]
  \chemical[sixring,SIX,RZ246]
           [A,B,C]
\stopchemical
\end{document}