LaTeX-examples/tikz/chemistry-example/chemistry-example.tex

\documentclass[varwidth=true, border=2pt]{standalone}
\usepackage{chemfig,chemmacros}
% Source: http://www.latex-community.org/know-how/latex/51-latex-math-science/434-chemistry-molecules
% See Source for explanations

\begin{document}
    \begin{center}
        \small\setatomsep{1.5em}
        \schemestart
        \chemfig{*6(=-=(-(=[2]O)-[::-60]O-[0]O-[::30](=[2]O)-[::-60]*6(=-=-=-))-=-)}
        \arrow{->[$\Delta$]}
        2 \chemfig{*6(=-=(-(=[2]O)-[::-60]\lewis{0.,O})-=-)}
        \arrow
        2 \chemfig{*6(=-=(-[,.15,,,draw=none]\lewis{0.,})-=-)}\+\ch{2 CO2 ^}
        \schemestop
    \end{center}
\end{document}