How to represent a chemical reaction network

What is the simplest way to represent a reaction network using LaTeX? An example of a reaction network is shown below:

• Maybe \xymatrix? – Arun Debray Jan 31 '16 at 22:33

chemfig can do this:

\documentclass{article}
\usepackage{chemfig}
\begin{document}
\schemestart
\subscheme{B + E}
\arrow(be--ac)[135]
\subscheme{A + C}
\arrow[90]
\chemfig{A}
\arrow{<=>}
\chemfig{B}
\arrow(@be--d){<=>}[45]
\chemfig{D}
\arrow(@ac--@d){<=>}
\schemestop
\end{document}