我对 chemfig 中的箭头有问题

Question

箭头的尖端位置不正确，它们稍微向左偏移了。有人知道如何修复它以便它们可以位于中间吗？

    \documentclass{article}
    \usepackage{chemformula}
    \usepackage{chemfig}
\usepackage{chemmacros}
    \begin{document}
    \schemestart
        \chemfig{@{a1}Cl-[@{a2},.8]@{a3}\textcolor{red}{H}} 
        \+ 
        \chemfig{@{a4}\textcolor{blue}{\charge{0=\: , 180=\:}{O}}(-[:65,.6]H)-[:-65,.6]H} 
        \ch{<>} 
        \chemfig{\textcolor{blue}{\charge{0=\: , 125:3pt=\scriptsize $ \oplus $}{O}}(-[:65,.6]H)(-[:180,.6]\textcolor{red}{H})-[:-65,.6]H}
        \+
        \chemfig{\charge{25:3pt=\scriptsize $\ominus$}{Cl}}
    \schemestop
    \chemmove{
        \draw(a2)..controls +(85:4mm) and +(105:4mm)..(a1);
        \draw(a4.135)..controls +(100:4.5mm) and +(80:4.5mm)..(a3);}
    \end{document}

现在的情况就是这样。

Answer 1

当我在最新版本的 latex（texlive 2023）中编译您的代码时，结果还不错。

我调整了箭头上的一些数字，并添加了一些选项。

\documentclass{article}
\usepackage{chemformula}
\usepackage{chemfig}
\usepackage{chemmacros}
\begin{document}
    \schemestart
    \chemfig{@{a1}Cl-[@{a2},.8]@{a3}\textcolor{red}{H}} 
    \+ 
    \chemfig{@{a4}\textcolor{blue}{\charge{0=\:,180=\:}{O}}(-[:65,.6]H)-[:-65,.6]H} 
    \ch{<>} 
    \chemfig{\textcolor{blue}{\charge{0=\: , 125:3pt=\scriptsize $ \oplus $}{O}}(-[:65,.6]H)(-[:180,.6]\textcolor{red}{H})-[:-65,.6]H}
    \+
    \chemfig{\charge{25:3pt=\scriptsize $\ominus$}{Cl}}
    \schemestop
    \chemmove{
        \draw[red,shorten <=1pt,shorten >=1pt](a2)..controls +(90:4mm) and +(80:6mm)..(a1);
        \draw[red,shorten <=3pt,shorten >=1pt](a4.180)..controls +(90:8mm) and +(80:5mm)..(a3);}
\end{document}

Answer 2

作为@CrocoDuck 的好答案的一个小变化：你可以使用to路径操作而不是贝塞尔曲线来获得看起来更对称的箭头：

\documentclass{article}
\usepackage{chemformula}
\usepackage{chemfig}
\usepackage{chemmacros}
\begin{document}
    \schemestart
    \chemfig{@{a1}Cl-[@{a2},.8]@{a3}\textcolor{red}{H}} 
    \+ 
    \chemfig{@{a4}\textcolor{blue}{\charge{0=\:,180=\:}{O}}(-[:65,.6]H)-[:-65,.6]H} 
    \ch{<>} 
    \chemfig{\textcolor{blue}{\charge{0=\: , 125:3pt=\scriptsize $ \oplus $}{O}}(-[:65,.6]H)(-[:180,.6]\textcolor{red}{H})-[:-65,.6]H}
    \+
    \chemfig{\charge{25:3pt=\scriptsize $\ominus$}{Cl}}
    \schemestop
    \chemmove{
        \draw[red,shorten <=1pt,shorten >=1pt](a2) to [out=90,in=80,looseness=2.5] (a1);
        \draw[red,shorten <=3pt,shorten >=1pt](a4.180) to [out=100,in=80,looseness=1.5] (a3);}
\end{document}