# Arrow label on Chemfig image?

I have this code:

\documentclass[varwidth, margin=2cm, png]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[english, ngerman, danish]{babel}
\pagestyle{empty}
\usepackage{chemfig}
\usepackage{lipsum}
\begin{document}
\chemfig{R'-[9]-[7]-[9](-[7]R'')=[10]O}
\end{document}

I just want arrows with letters on to point on each carbon, and one to point at oxygen. I don't know how to do it. Maybe you can help?

• I'm not sure, you want arrows to point to the two Rs and to O? May 8 '15 at 18:52
• @Alenanno To the carbons and to the O :-) May 8 '15 at 19:04
• That does something: \chemfig{R'-[9]-[7]-[9](-[7]R'')=[10]@{O}O} \chemmove{\draw[<-] (O) -- + (45:1);} Unfortunately it doesn't update the bounding box. The manual has a lot more examples. May 8 '15 at 19:50

Do you mean something like this? It uses the fact that chemfig's formulas are tikzpictures. chemfig offers the possibility to give explicite names to the nodes in a formula using @{name} (this is explained in the manual). Later one can refer to those nodes in a seperate tikzpicture. \chemmove simply is a wrapper for a tikzpicture with the options remember picture, overlay, both of which are explained in the TikZ manual.

\documentclass[varwidth, margin=2cm, png]{standalone}
\usepackage{chemfig}
\begin{document}

\chemfig{R'-[:30]@{C3}-[:-30]@{C2}-[:30](-[:-30]R'')=[2]@{O}O}
\chemmove[shorten <=2pt]{
\draw[<-] (C3) --++(0,1) node[above] {carbon} ;
\draw[<-] (C2) --++(0,-1) node[below] {carbon} ;
\draw[<-] (O) --++(1,.5) node[right] {oxygen} ;
}

\end{document}