Resonance structure of acetate

Question

I need to draw a scheme to show the stabilization of the acetate ion by resonance and I'm going crazy :-( I started using chemfig not so long ago and it seems that I need a lot more practice! In the meanwhile, can anybody help me solve the problem? I would like something like this

But I failed already by adding the first arrow :-(

\documentclass{article}
\usepackage{chemfig}
\begin{document}
\schemestart
\chemfig{R-C(=[1]{@{a1}\lewis{2:0:,O}})[@{db}](-[7]{\lewis{0:4:6:,{\chemabove{O}{\scriptstyle\hspace{3mm}\ominus}}}})}
\arrow{<->}
\chemfig{R-C(=[1]{\lewis{2:0:,O}})(-[7]{\lewis{0:4:6:,{\chemabove{O}{\scriptstyle\hspace{3mm}\ominus}}}})}
\arrow{<->}
\chemfig{R-C(=[1]{\lewis{2:0:,O}})(-[7]{\lewis{0:4:6:,{\chemabove{O}{\scriptstyle\hspace{3mm}\ominus}}}})}
\schemestop
\chemmove{\draw(db).. controls +(100:5mm) and +(145:5mm).. (a1);}
\end{document}

Answer 1

Probably something like this?

\documentclass[
    crop,
    border=5,
    tikz=true,
    multi={page},
    12pt
]{standalone}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{mathtools}
\usepackage{chemmacros}
\chemsetup{
    modules = all,
}
\usepackage{chemfig}
    \setchemfig{
        angle increment = 15,
        atom sep = \bndlen,
        bond offset = 0.5pt,
        double bond sep = 3pt,
        compound sep = 5.0em,
        arrow coeff = 1,
        arrow offset = 12pt,
        scheme debug = false,
        bond join = true,
        chemfig style={line width=\lnwidth},
        arrow style={line width=\lnwidth},
    }

\newcommand{\bndlen}{2.0em}
\newcommand{\lnwidth}{0.7pt}

\begin{document}

\begin{page}
\schemestart
    \chemleft{[}
    \subscheme{
        \chemfig{
            CH_3
            -C
            (-[::-45]\lewis{1:5:7:,O}\rlap{\color{purple}{${\ }^-$}})
            =[@{b1}::45]@{o1}\lewis{1:3:,O}
        }
        \arrow{<->}
        \chemfig{
            CH_3
            -C\rlap{\color{teal}{${}^+$}}
            (-[@{b2}::-45]\lewis{1:5:7:,O}@{o2}\rlap{\color{purple}{${\ }^-$}})
            -[::45]\lewis{1:3:7:,O}\rlap{\color{purple}{${\ }^-$}}
        }
        \arrow{<->}
        \chemfig{
            CH_3
            -C
            (=[::-45]\lewis{5:7:,O})
            -[::45]\lewis{1:3:7:,O}\rlap{\color{purple}{${\ }^-$}}
        }
        \chemmove{
            \draw[shorten <=3pt,shorten >=1pt,purple](b1)..controls +(-15:10mm) and +(-30:5mm)..(o1);
            \draw[shorten <=3pt,shorten >=1pt,purple](o2)..controls +(90:5mm) and +(45:5mm)..(b2);
        }
    }
    \chemright{]}
\schemestop
\end{page}

\end{document}

Also, if you are after a picture-perfect replica, note that the font family used in your illustration is most likely proprietary ITC New Baskerville. In order to use it, you have to obtain the font or use a free alternative from The LaTeX Font Catalogue; it would be easier to compile with XeLaTeX at this point.

Answer 2

Here are two possible version of the first reaction step with two variants of the arrow. The exact parameters might however still need some fine tuning.

\documentclass{article}
\usepackage{chemfig}
\begin{document}
\schemestart
\chemfig{R-C(=[@{db}1]{@{a1}\lewis{2:0:,O}})(-[7]{\lewis{0:4:6:,{\chemabove{O}{\scriptstyle\hspace{3mm}\ominus}}}})}
\schemestop
\chemmove{\draw(db).. controls +(100:5mm) and +(145:5mm).. (a1);}

\vspace{1.5cm}

\schemestart
\chemfig{R-C(=[@{db}1]{@{a1}\lewis{2:0:,O}})(-[7]{\lewis{0:4:6:,{\chemabove{O}{\scriptstyle\hspace{3mm}\ominus}}}})}
\schemestop
\chemmove{\draw[shorten <=4pt,shorten >=4pt](db).. controls +(10:5mm) and +(-10:10mm).. (a1);}
\end{document}

With color:

\documentclass{article}
\usepackage{chemfig}
\begin{document}
\schemestart
\chemfig{R-C(=[@{db}1]{@{a1}\lewis{2:0:,O}})(-[7]{\lewis{0:4:6:,{\chemabove{O}{\scriptstyle\hspace{3mm}\color{red}\ominus}}}})}
\schemestop
\chemmove{\draw[shorten <=4pt,shorten >=4pt, color=red](db).. controls +(10:5mm) and +(-10:10mm).. (a1);}
\end{document}