# latex loop back formula arrow

I would like to create an equation where 2nd equation is inupt to the first one. I want to write the equation in a figure.

I try using long arrow a

\begin{align}
%\begin{split}
\rightarrow  \dotr{R}+O_2  &\longrightarrow \dotr{R00}
%\end{split}
\label{}
\end{align}

\begin{align}
%\begin{split}
\dotr{R00} + RH &\longrightarrow ROOH + \dotr{R} \bigg\uparrow
%\end{split}
\label{}
\end{align}

• – Bibi Jul 22 '20 at 13:25
• \begin{align} %\begin{split} \rightarrow \dotr{R}+O_2 &\longrightarrow \dotr{R00} %\end{split} \label{} \end{align} \begin{align} %\begin{split} \dotr{R00} + RH &\longrightarrow ROOH + \dotr{R} \bigg\uparrow %\end{split} \label{} \end{align} – WBAN_crypto Jul 22 '20 at 13:40
• your code does not compile – js bibra Jul 22 '20 at 14:23
• Where does the \dotr command come from? – Bernard Jul 22 '20 at 14:41

The equation in the figure is a chemical equation. Using Bernard's answer and the mhchem package (useful for writing chemical formulas, etc.), following is the code which you may use. The mhchem package takes care of the radical dots in the chemical equation.

\documentclass{article}

\usepackage{amsmath}
\usepackage{pst-node}

\usepackage[version=4, arrows=pgf-filled]{mhchem}

\begin{document}

\begin{align}
&\rnode{R1}{\ce{R^{.}}} + \ce{O2 -> ROO^{.}} \\
&\ce{ROO^{.} + RH ->}\rnode{R2}{\ce{R^{.}}}
%
\psset{linewidth=0.5pt, arrows=<-, arrowinset=0.5, nodesep=2pt}
\ncloop[angleA=180, armA=1cm, angleB=-90, armB=0.20cm, linearc=0]{R1}{R2}%
\end{align}
\end{document}


• thank you for the reply. The bottom arrow is not appearing similarly to the previous answer. – WBAN_crypto Jul 22 '20 at 17:57
• I am using my university class file – WBAN_crypto Jul 22 '20 at 18:03
• How are you compiling the code? Compile the code using XeLaTeX or do this LaTex (x2) -> DVItoPS -> PStoPDF. – Tanvir Jul 22 '20 at 21:40
• I am using overleaf – WBAN_crypto Jul 23 '20 at 13:17
• In Overleaf, from setting menu, change the compiler from pdfLaTex to XeLaTex. You can get the settings by clicking the menu at the top left of Overleaf. – Tanvir Jul 23 '20 at 13:32

You can use the \ncloop command from pst-node:

\documentclass{article}

\usepackage{amsmath}
\newcommand{\dotr}[1]{#1^{\bullet}}
\usepackage{pst-node}

\begin{document}

\begin{align}
\rnode{R1}{ \dotr{\mathrm{R}}}+\mathrm{O}_2 &\longrightarrow \dotr{\mathrm{ROO}}\\
\dotr{\mathrm{ROO}} + \mathrm{RH} &\longrightarrow \mathrm{ROOH} +\dotr{ \rnode{R2}{\mathrm{R}}}
%
\psset{linewidth=0.5pt, arrows=<-, arrowinset=0.2, nodesep=2pt}
\ncloop[angleA=180, armA=1cm, angleB=-90, armB=0.20cm, linearc=0.05]{R1}{R2}%
\label{}
\end{align}

\end{document}


• thank you very much for your reply. I don't know why the bottom arrow is not appearing in my document. Do I need to add any other package? thanks. – WBAN_crypto Jul 22 '20 at 17:56
• I am using my university article class – WBAN_crypto Jul 22 '20 at 18:02