This is benzene:
\usepackage{chemfig}
\begin{document}
\chemfig{**6(------)}
\end{document}
- Circle represents delocalized electrons.
- This delocalization of gives rise to resonance, where the three double-bonds continuously switch between each other:
\def\pgfsysdriver{pgfsys-xetex.def}
\usepackage{chemfig}
\begin{document}
\chemfig{*6(=-=-=-)}
\schemestart
\arrow{<=>}
\schemestop
\chemfig{*6(-=-=-=)}
\end{document}