# chemfig: align multiple reactions

How can I align multiple reactions to the reaction arrow using chemfig?

In the MWE, I want to align the two reactions to the arrow.

\documentclass{minimal}
\usepackage{chemfig}

\begin{document}

\chemfig{Cl}\chemsign+\chemfig{O_3}
\chemrel{->}
\chemfig{ClO}\chemsign+\chemfig{O_2}

\chemfig{ClO}\chemsign+\chemfig{O}
\chemrel{->}
\chemfig{Cl}\chemsign+\chemfig{O_2}

\end{document}


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• Here's a chemfig only way: use its \startscheme ... \stopscheme mechanism in combination with the invisible »arrow« 0 and the anchoring of TikZ nodes. The trick here:

\arrow(@c1.south east--.north east){0}[-90,.1]


an invisible arrow {0} pointing downwards (-90) and shortened (.1) that connects compound c1 with a new one, the former anchored south east and the latter north east. You can see what chemfig treats as compounds if you add \schemedebug{true} before the scheme.

\documentclass{article}
\usepackage{chemfig}
\begin{document}
\schemestart
Cl \+ \printatom{O_3} \arrow ClO \+ \printatom{O_2}
\arrow(@c1.south east--.north east){0}[-90,.1]
ClO \+ O \arrow Cl \+ \printatom{O_2}
\schemestop
\end{document}


• As you've noted in your own answer chemfig can also be used in combination with amsmath's alignment environments, similar to the following proposals

• Simple reactions like the ones shown in the question can also be typeset with mhchem and amsmath:

\documentclass{article}
\usepackage{mhchem}
\usepackage{amsmath}
\begin{document}
\begin{align*}
\cee{Cl + O3 &-> ClO + O2} \\
\cee{ClO + O &-> Cl + O2}
\end{align*}
\end{document}


• Another possibility would be chemformula with amsmath oder chemmacros:

\documentclass{article}
\begin{document}
\begin{align*}
\ch{Cl + O3 &-> ClO + O2} \\
\ch{ClO + O &-> Cl + O2}
\end{align*}
\begin{reactions*}
Cl + O3 &-> ClO + O2 \\
ClO + O &-> Cl + O2
\end{reactions*}
\end{document}


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The last approach is what I was after for, thank you! A bit of a hax, but does the trick. –  Mappi Jul 27 at 16:43
I believe that the 0 arrow is there for such purposes. I often find it very useful! –  cgnieder Jul 27 at 16:46

chemfig can be used inside align environment. Thus, it can be done as

\documentclass{minimal}
\usepackage{chemfig}
\usepackage{amsmath}

\begin{document}

\begin{align*}
\chemfig{Cl}\chemsign+\chemfig{O_3}
& \chemrel{->}
\chemfig{ClO}\chemsign+\chemfig{O_2} \\
\chemfig{ClO}\chemsign+\chemfig{O}
& \chemrel{->}
\chemfig{Cl}\chemsign+\chemfig{O_2}
\end{align*}

\end{document}


The downside of this answer is that the reactions are inside align and not chemfig. For example, you cannot scale the equations easily.

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