carbonlabel is a LaTeX package that draws simple molecules with 13C labeled carbon atoms.
The package is currently under heavy development and not intended for productive usage!
Simple example:
\documentclass{minimal}
\usepackage{carbonlabel}
\begin{document}
% 6 atoms, 2 per row, uniformly 13C labeled
\labeling{2,2,2}{u} [U-\textsuperscript{13}C] Glucose
\\[.5cm]
% 6 atoms, in one row, 1,2-13C labeled
\labeling{6}{1,2} [1,2-\textsuperscript{13}C] Glucose
\end{document}Produces:
