答案1
您应该使用 chemfig 手册中的代码 setpolymerdelim 进行编写
\documentclass{article}
\usepackage{chemfig}
\begin{document}
\newcommand\setpolymerdelim[2]{\def\delimleft{#1}\def\delimright{#2}}
\def\makebraces[#1,#2]#3#4#5{%
\edef\delimhalfdim{\the\dimexpr(#1+#2)/2}%
\edef\delimvshift{\the\dimexpr(#1-#2)/2}%
\chemmove{%
\node[at=(#4),yshift=(\delimvshift)]
{$\left\delimleft\vrule height\delimhalfdim depth\delimhalfdim
width0pt\right.$};%
\node[at=(#5),yshift=(\delimvshift)]
{$\left.\vrule height\delimhalfdim depth\delimhalfdim
width0pt\right\delimright_{\rlap{$\scriptstyle#3$}}$};}}
\setpolymerdelim[]
\chemfig{-[@{left,0.3},1.5]C(-[:90]*6(=-=-=-))(-[6]H)-C(-[2]H)(-[6]H)-[@{right,0.8}]}
\makebraces[90pt,30pt]{n}{left}{right}
\end{document}