Alignment of chemfig molecules in a reaction

Question

I'm using chemfig for my chemistry course this period, and facing problems with the alignment of the molecules, arrows, + signs and also the names. Basically everything is messed up haha.

Can someone explain me how to do it right? I would like to have the molecules' center on one horizontal line, the arrows and + signs aligning that line and the names aligned horizontally just below the biggest molecule.

Thanks in advance, Lisa

    \begin{figure}[width=\textwidth]
    \scriptsize
    \begin{scheme}
    \schemestart
    \chemname{\chemfig{OH-[:210,,1]-[:270]=_[:210]-[:150]=_[:90]-[:30](=_[:330])-[:90](-[:30,,,1]OH)=[:150]O}}{salicylic acid}
    \+{2em}
    \chemname{\chemfig{-[:30](=[:90]O)-[:330]O-[:30](-[:330])=[:90]O}}{acetic anhydride}
    \arrow{->}
    \chemname{\chemfig{OH-[:210,,1](=[:150]O)-[:270]=_[:330](-[:30]O-[:330](=[:270]O)-[:30])-[:270]=_[:210]-[:150]=_[:90](-[:30])}}{acetylsalicylic acid}
    \+{2em}
    \chemname{\chemfig{-[:30](-[:330,,,1]OH)=[:90]O}}{acetic acid}
    \schemestop
    \end{scheme}
    \caption{Reaction for synthesizing acetylsalicylic acid} \label{fig:reaction}
    \end{figure}

Answer 1

The main secret is starting the molecules with the right atom: the first atom of a formula determines the baseline of the corresponding molecule. The rest is only shifting the arrow a bit using its optional argument as described in the manual:

\documentclass{article}
\usepackage{chemfig}

\begin{document}

\begin{center}
  \setatomsep{1.8em}
  \small
  \schemestart
    \chemname{%
      \chemfig{
        OH-[:210,,1]-[:270]=_[:210]-[:150]
        =_[:90]-[:30](=_[:330])
        -[:90](-[:30,,,1]OH)=[:150]O}%
    }{salicylic acid}
    \+
    \chemname{%
      \chemfig{
        (-[:-150])(=[:90]O)-[:330]O-[:30](-[:330])=[:90]O}%
    }{acetic anhydride}
    \arrow{->[][][9pt]}
    \chemname{%
      \chemfig{
        {\vphantom{H}}-[:-150](=[:-90]O)-[:150]
        O-[:210,,1]-[:270]=_[:210]-[:150]
        =_[:90]-[:30](=_[:330])
        -[:90](-[:30,,,1]OH)=[:150]O}%
    }{acetylsalicylic acid}
    \+
    \chemname{%
      \chemfig{(-[:-150])(-[:330,,,1]OH)=[:90]O}%
    }{acetic acid}
  \schemestop
\end{center}

\end{document}