这取决于实际用例,但也许只是一个+
节点circle
?
\documentclass[border=20pt]{standalone}
\usepackage{chemfig}
\begin{document}
\chemfig{[:30]-@{x}(-[:90])-[:330]}
\chemmove{
\node[shift={(10pt,5pt)}, circle, draw, inner sep=0pt] (plus) at (x) {+};
\node[anchor=west] at (plus.east) {$\neq\oplus$};
}
\end{document}