# electronegativity brackets with chemfig (?)

I've been trying to draw something like this with chemfig:

Specifically I'm trying to create those red brackets around the bonds indicating that due the Oxygen's higher electronegativity, it has a greater pull on the electrons than Hydrogen.

Since I never learned chemistry in English, I have no idea how these things are called (or even if they are used in actual chemistry?), that's why I apologize having to ask this question.

Here it is. chemfig basically works like Tikz. You can set nodes and use those nodes to draw arrows, etc.

I did the brackets by drawing arcs, and setting nodes on the lines. It would have been easier if each "atom" was a node, but I haven't found anything in the documentation. In any case, if you discover something like that, you can remove the extra nodes and use the atoms themselves as a base for other graphics.

I also added \pgfresetboundingbox to remove some extra white space that was appearing on the right. Not much, but it was noticeable enough.

## Code

\documentclass[margin=10pt]{standalone}
\usepackage{chemfig}

\begin{document}

\chemfig{H-[@{a1}:45]O-[@{a2}:-45]H}\pgfresetboundingbox

\chemmove{\draw[red,thick] (a1)+(-8.3pt,-2.8pt) arc (-180:-90:5pt);}\pgfresetboundingbox
\chemmove{\draw[red,thick] (a2)+(3pt,-7.8pt) arc (-90:0:5pt);}

\end{document}

• Works great, thanks. As I'm not that experienced with TeX, I'd like to ask if there would be a theoretical way to directly implement this via a macro (?) to simplify it? Something like C((-[:0]O) to draw it into the bond (probably not). Any generalization would be nice. – Philip K. May 8 '15 at 20:43
• @user3107501 You're welcome! :) – Alenanno May 8 '15 at 20:45
• @user3107501 I didn't get notified of your comment edit. Anyway, if you mean remove those commands and place them in the preamble, you can issue a \newcommand. I think it would work. But I never worked with chemfig so I don't know off the top of my head. :D – Alenanno May 9 '15 at 13:16