How to get text above and below double harpoon (reversible reaction) symbols in an equation

Question

I'm working on the Chemwiki Dynamic Textbook Project at UC Davis, California and I've run into a problem. I need to formulate a symbol containing double harpoons (as in a reversible reaction, e.g. \rightleftharpoons); however, I need to have text both above and below the harpoons. I have an image I can email, but I can't post with an image because I'm new to this.

I can find code for \overleftrightarrow and \underleftrightarrow, but that's not quite what I need. I need both, on the same expression. If anyone has a minute to help me, I would greatly appreciate it!

If you don't mind using TikZ, a quite similar (if not the same) problem was solved in this question. — sgbmyr, Apr 04 '11 at 23:26

score 31 · Answer 1 · edited Jun 15 '23 at 17:59

31

You could use the features provided by the mhchem package. A little example, taken from the package documentation:

\documentclass{article}
\usepackage{mhchem}
\begin{document}
\ce{
Zn^2+
<=>[\ce{+ 2OH-}][\ce{+ 2H+}]
$\underset{\text{amphoteres Hydroxid}}{\ce{Zn(OH)2 v}}$
<=>[\ce{+2OH-}][\ce{+ 2H+}]
$\underset{\text{Hydroxozikat}}{\ce{[Zn(OH)4]^2-}}$
}
\end{document}

The result:

edited Jun 15 '23 at 17:59

Gennaro Arguzzi

1,895

answered Apr 04 '11 at 22:48

Gonzalo Medina

505,128

I think there is a typo in the last line: It should be "\ce{[Zn(OH)4]^2-}", right? – user408858 Mar 09 '22 at 19:11

Fred Senese · Answer 2 · 2014-07-07T19:54:34.407

17

\documentclass{article}
\usepackage{mathtools}
\begin{document}

$\mathrm{A} \xrightleftharpoons[k_2]{k_1} \mathrm{B}$

\end{document}

edited Jul 07 '14 at 19:54

answered Jul 02 '14 at 23:25

Fred Senese

271

Welcome, can you please extend your answer to cover the duplicate suggested under the question? – percusse Jul 02 '14 at 23:49
done. I replaced \rightleftharpoons with \xrightleftharpoons. – Fred Senese Jul 05 '14 at 17:55
\rm was deprecated around twenty years ago. It's not part of the LaTeX commands. – Manuel Jul 05 '14 at 19:12
Yes, I know. It still works, though, and it's shorter than \mathrm but point taken. I edited my response. – Fred Senese Jul 07 '14 at 19:50

score 11 · Answer 3 · answered Oct 08 '14 at 11:38

11

A simple one-line solution which worked for me was:

X \underset{k_2}{\stackrel{k_1}{\rightleftharpoons}} Y

enter image description here

But the harpoon arrows don't extend when the text above and below is longer.

answered Oct 08 '14 at 11:38

edison1093

121

score 7 · Answer 4 · edited Apr 13 '17 at 12:35

An alternative to mhchem would be the chemmacros bundle (including chemformula) by our user @cgnieder.

The syntax is simple and (pretty) intuitive, in many ways similar to the syntax of mhchem.

Here is a minimal example and the output.

\documentclass[border=10pt]{standalone}
\usepackage{chemformula}%loaded by chemmacros
\begin{document}
\ch{Zn^2+ 
<>[ + 2 OH- ][ + 2 H+ ]%Reaction in both directions
!(amphoteres~Hydroxid)( Zn(OH)2 v )
<=>[ + 2 OH- ][ + 2 H+ ]%Equilibrium arrow
!(Hydroxozikat)( [Zn(OH)4]^2- )
}
\end{document}![chemmacros output][1]

There is much more handy stuff in the bundle. Check out the documentation for more or the blog of the author.

How to get text above and below double harpoon (reversible reaction) symbols in an equation

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