Mit dem Tipp `\raisebox{5ex}{$\oplus$}` von @Henri ergibt sich: \documentclass{article} \usepackage{chemfig} \renewcommand*\printatom[1]{\ensuremath{\mathsf{#1}}} \setchemfig{atom sep = 2.3em, cram width = 4pt, lewis sep = 3pt } \begin{document} \begin{center} \chemname{\chemleft[ \chemfig{R-[:30]\chemabove{\lewis{2,O}} {\hspace{3.15cm}\oplus}(>:[:-20]R{''})<[:-70]R^{'}} \chemright]}{\textbf{I}} \hspace{1.5cm} \chemname{\chemleft[ \chemfig{H-[:30]\lewis{2,O}(>:[:-20]H)<[:-70]H} \chemright]\raisebox{5ex}{$\oplus$}}{\textbf{II}} \end{center} \end{document}

\documentclass{article} \usepackage{chemfig} \renewcommand*\printatom[1]{\ensuremath{\mathsf{#1}}} \setchemfig{atom sep = 2.3em, cram width = 4pt, lewis sep = 3pt } \begin{document} \begin{center} \chemname{\chemleft[ \chemfig{R-[:30]\chemabove{\lewis{2,O}} {\hspace{3.15cm}\oplus}(>:[:-20]R{''})<[:-70]R^{'}} \chemright]}{\textbf{I}} \hspace{1.5cm} \chemname{\chemleft[ \chemfig{H-[:30]\lewis{2,O}(>:[:-20]H)<[:-70]H} \chemright]\raisebox{5ex}{$\oplus$}}{\textbf{II}} \end{center} \end{document}