这不是一个完整的答案。只是一个提示!
\documentclass{article}
\usepackage{chemfig}
\usetikzlibrary{calc}
\begin{document}
\chemfig{C(-[:60]CH_2CH_2CH_3)(-[:180]@{Br}Br)(<[:280]CH_2CH_3)(<:[:320]CH_3)}
\chemmove{
\draw[red,latex-](Br) ..controls +(70:4mm) and +(90:10mm) .. ($(Br)+(0.5,0.05)$);
}
\end{document}
![在此处输入图片描述](https://i.stack.imgur.com/P5ohN.png)