# Arrival atom numbering doesn't work with \chemabove

Consider the following MWE:

\documentclass{article}
\usepackage{chemfig}

\begin{document}

\chemfig{
X
-[:30,,,2]^{18}\chemabove{O}{H}
-[:-30]X
}

\end{document}


This code returns an error:

Package chemfig Error: no atom found at position 2, pershaps you mispelled the optional argument of the bond.. }


Elimination of the number 2 as an argument for the arrival oxygen atom resolves that issue, but the left X-O bond is placed incorrectly:

\chemfig{
X
-[:30]^{18}\chemabove{O}{H}
-[:-30]X
}


I've been playing around a bit and the best hack I've came up so far is to use a shortened invisible O-H bond:

\chemfig{
X
-[:30,,,2]^{18}O(-[:90,0.3,2,,draw=none]H)
-[:-30]X
}


Still, I find the latter solution less robust and elegant. Is there a way to still use \chemabove or \chembelow in tandem with departure/arriving atom numbering arguments?

I guess, you need to put the 18 into the stack and reduce its bounding box to zero using \llap (a similar example using \rlap is provided in the current documentation [v1.33] on page 42):

\documentclass[border=5mm]{standalone}
\usepackage{chemfig}

\begin{document}

\chemfig{
X
-[:30]\chemabove{\llap{$^{18}$}O}{H}
-[:-30]X
}

\end{document}


You should use | to start the 2nd atom after ^{18}:

\chemfig{
X
-[:30,,,2]^{18}|\chemabove{O}{H}
-[:-30]X
}

• Nice! I forgot this one! Thanks for pointing it out – Jasper Habicht Dec 8 '18 at 14:07