How to type curved arrows and type a text over these arrows

Question

I would like to write the following picture. I am using the package chemfig but I am not sure how to write curved arrows and type over it.

Answer 1

For example with tikz-cd

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
\begin{tikzcd}[every cell/.style={shape=circle,inner sep=0.5ex,font=\large}]
A \rar{a} \ar[r,bend right=60,looseness=1.8]& B \rar{b}                     & C \rar{c}\ar[dr,"e"']  & D \ar[d,bend right] \\
                                            & F \ar[u]\ar[rr,"f",pos=0.4]   &                        & E
\end{tikzcd}
\end{document}

Answer 2

A chemfig solution:

\documentclass{article}
\usepackage{chemfig}

% from documentation:
%http://mirror.kku.ac.th/CTAN/macros/generic/chemfig/chemfig-en.pdf
\makeatletter
\definearrow1{s>}{%
    \ifx\@empty#1\@empty
    \expandafter\draw\expandafter[\CF@arrow@current@style,-CF](\CF@arrow@start@node)--(\CF@arrow@end@node);%
    \else
    \def\curvedarrow@style{shorten <=\CF@arrow@offset,shorten >=\CF@arrow@offset,}%
    \CF@expadd@tocs\curvedarrow@style\CF@arrow@current@style
    \expandafter\draw\expandafter[\curvedarrow@style,-CF](\CF@arrow@start@name)..controls#1..(\CF@arrow@end@name);
    \fi
}
\makeatother


\begin{document}
%   \schemedebug{true} % for debugging only
    \schemestart
    A \arrow(aa--bb){->[a]} B \arrow(--cc){->[b]} C \arrow(--dd){->[c]} D
    \arrow(@bb--ff){<-}[-90] F \arrow(--ee){->[f]}[,2.15] E
    \arrow(@cc--@ee){->[][*{0}e]}
    \arrow(@aa--@bb){s>[+(-45:1.5cm)]}
    \arrow(@dd--@ee){s>[+(210:1cm)and+(120:1cm)]}
    \schemestop
\end{document}

I obtained the code for the curved arrow (s>) from the documentation, IV Reaction schemes 10 Arrows customization, and its use is very well documented there as well.

An alternative (instead of s>) would probably be using \chemmove and the controls.. etc. from TikZ, but I didn't try that.