1 Answer
You can define your own new arrow type =retro>
as shown in the following MWE. Text above and below the arrow can be added using the first two optional arguments as described in section 9 of the chemfig
manual.
\documentclass{article}
\usepackage{chemfig}
\catcode`\_=11
\definearrow3{=retro>}{%
\CF_arrowshiftnodes{#3}%
\draw[double distance=2pt, -Implies] (\CF_arrowstartnode)--(\CF_arrowendnode);
\expandafter[\CF_arrowcurrentstyle](\CF_arrowstartnode)--(\CF_arrowendnode);%
\CF_arrowdisplaylabel{#1}{0.5}+\CF_arrowstartnode{#2}{0.5}-\CF_arrowendnode
}
\catcode`\_=8
\begin{document}
\schemestart
A \arrow{=retro>} B
\schemestop
\schemestart
A \arrow{=retro>[above][below]} B
\schemestop
\end{document}
MWE which works with oder versions of chemfig
, previous to version 1.4:
\documentclass{article}
\usepackage{chemfig}
\makeatletter
\definearrow3{=retro>}{%
\CF@arrow@shift@nodes{#3}%
\draw[double distance=2pt, -Implies] (\CF@arrow@start@node)--(\CF@arrow@end@node);
\expandafter[\CF@arrow@current@style](\CF@arrow@start@node)--(\CF@arrow@end@node);%
\CF@arrow@display@label{#1}{0.5}+\CF@arrow@start@node{#2}{0.5}-\CF@arrow@end@node
}
\makeatother
\begin{document}
\schemestart
A \arrow{=retro>} B
\schemestop
\schemestart
A \arrow{=retro>[above][below]} B
\schemestop
\end{document}