latex loop back formula arrow

Question

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} bigguparrow
  %end{split}
     label{}
end{align}

Tanvir · Answer

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}

Bernard · Answer

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}

latex loop back formula arrow

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