Chemfig - Name some compounds under a single label

Question

I know within the chemfig package compounds can be named with the command \chemname. Is there a way to label some compounds under a single label? For example, put a label "Reactants" under the reactants in a reactions scheme.

In the following example:

\documentclass{article}
\usepackage{chemfig,chemmacros}
\begin{document}

\schemestart
\chemfig{R-[:30](=[:90]O)-[:-30]R}
\arrow{0}[,.5]
\chemfig{R'-[:30](=[:90]O)-[:-30]R'}
\arrow{0}[,1.5]
\chemfig{R'-[:30](=[:90]O)-[:-30]R}
\schemestop

\end{document}

I can put a label under the third compound with \chemname, but how can I put a single label under the first two compounds?

Answer 1

If you place the first two compounds in a \subscheme{...} the whole subscheme gets a unique name that you can refer to in an arrow using the \arrow{@<name>--) syntax:

\documentclass{article}
\usepackage{chemfig}
\begin{document}

% uncomment to see the names:
% schemedebug{true}
\schemestart
\subscheme{
  \chemfig{R-[:30](=[:90]O)-[:-30]R}
  \arrow{0}[,.5]
  \chemfig{R'-[:30](=[:90]O)-[:-30]R'}
}
\arrow{0}[,1.5]
\chemfig{R'-[:30](=[:90]O)-[:-30]R}
% use an invisible arrow pointing downwards to place the label text:
\arrow(@c1--){0}[-90,.1]
Below the first two compounds
\schemestop

\end{document}

Answer 2

I know Clemens loves \arrow{0} but his solution sounds complicated to me. Why don't you use \schemestart...\schemestop inside \chemname, which seems more natural?

\documentclass{article}
\usepackage{chemfig}
\begin{document}
\schemestart
\chemname{%
    \schemestart
        \chemfig{R-[:30](=[:90]O)-[:-30]R}
        \arrow{0}[,.5]
        \chemfig{R'-[:30](=[:90]O)-[:-30]R'}
    \schemestop
    }
    {One long name here!}
\arrow(.base east--.base west){0}[,1.5]
\chemfig{R'-[:30](=[:90]O)-[:-30]R}
\schemestop
\end{document}