Aligning atoms with arrows in chemfig

Question

I am writing a reaction scheme and tried to use Clemens recommendation (aligment...) i.e. "starting with the right atom", but I did not succeed to get what I wanted.

\documentclass[border = 0.5cm]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{chemfig}

\renewcommand\familydefault{\sfdefault}
\setarrowdefault{0,1.5,black,thick}
\setdoublesep{0.35700 em}  % 'Bond Spacing'
\setatomsep{1.78500 em}    % 'Fixed Length'
\setbondoffset{0.18265 em} % 'Margin Width'
\newcommand{\bondwidth}{0.06642 em} % 'Line Width'
\setbondstyle{line width = \bondwidth}
\renewcommand*\printatom[1]{\ensuremath{\mathsf{#1}}}

\begin{document}
\schemedebug{true}
\schemestart
    \chemname{%
        \chemfig{
            (-[:90]OH)-[:-30](-[:-90]OH)-[:30](-[:-30]H)=[:90]O}%
        }{\large{D,L-Glyceraldehyde}}
  \arrow{<<->[aldolase]}
    \chemname{%
        \chemfig{
            (-[:-150]H)(-[:-30]H)=[:90]O}%
        }{\large{Formaldehyde}}
    \+
    \chemname{%
        \chemfig{
            (-[:-90]OH)-[:30](-[:-30]H)=[:90]O}%
    }{\large{Glycolaldehyde}}
\schemestop
\end{document}

I would like to have the top carbon atoms aligned vertically with the arrow and the '+' sign also, but with this code this is not the case although I took care to start with them. The following picture shows what I would like to get:

Answer 1

The main thing to do is to set the anchor points that the arrow connects to (visible with scheme debug on.) with \arrow(.mid east--.mid west){<<->[aldolase]}.

Other notes:

• \setchemfig and the key-value syntax should be used instead starting from chemfig version 1.3 onwards. The individual \set... commands are deprecated.

• For the last molecule, to achieve what you want, you should start drawing the aldehyde carbon first (instead of the alcohol carbon).

• I added a little spacing around the \+ to fix the overlapping of chemnames.

• \large does not take an argument, do remove the braces after it.

MWE:

\documentclass[border = 1cm]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{chemfig}

\renewcommand\familydefault{\sfdefault}
\newcommand{\bondwidth}{0.06642 em} % 'Line Width'
\setchemfig{
    scheme debug = true,
    double bond sep = 0.35700 em,
    atom sep = 1.78500 em,
    bond offset = 0.18265 em,
    bond style = {line width=\bondwidth},
    arrow coeff = 1.5,
    arrow style = thick,
}
\renewcommand*\printatom[1]{\ensuremath{\mathsf{#1}}}

\begin{document}
    \schemestart
    \chemname{%
        \chemfig{
            (-[:90]OH)-[:-30](-[:-90]OH)-[:30](-[:-30]H)=[:90]O}%
    }{\large D,L-Glyceraldehyde}
    \arrow(.mid east--.mid west){<<->[aldolase]}
    \chemname{%
        \chemfig{
            (-[:-150]H)(-[:-30]H)=[:90]O}%
    }{\large Formaldehyde}
    \+{1.2em,1.2em}
    \chemname{%
        \chemfig{%
            (-[:210]-[6]OH)(=[2]O)-[:-30]H}%
    }{\large Glycolaldehyde}
    \schemestop
\end{document}