How to draw arrows for organic mechanism

Question

How can I draw the arrows for organic mechanism as in the attached pictures?

An edited MWE from the answer below:

\documentclass[a4paper, 10pt]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[french]{babel}
\usepackage{graphicx}
\usepackage{array}
\usepackage{chemfig}

\begin{document}
    \schemestart
        \chemfig{H-C(-[2]H)([6]-[@{sb1}]H)-[@{sb2}]\charge{0:3pt=$\scriptstyle\oplus$}{C}(-[2]H)(-[6]H)}
        \chemmove[-stealth, shorten >=2pt, shorten <=2pt, red]
            {\draw (sb1)..controls +(right:2mm) and +(down:3mm)..(sb2);}
        \arrow(.mid east--.mid west)
        \chemfig{H-C(-[2]H)=C(-[2]H)-H} + \chemfig{H^+}
    \schemestop
\end{document}

Answer 1

About organic reaction mechanisms: From the organic chemistry books I own, ALL use arrows to represent the movement of electrons, that is, where the electrons go.

The author of the images shown above uses arrows to show the atoms that will be "removed" from the molecule. I've never seen this before. If I needed to draw this reaction, I would do something like this:

\documentclass[a4paper, 10pt]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[french]{babel}
\usepackage{graphicx}
\usepackage{array}
\usepackage{chemfig}

\begin{document}
    \schemestart
    \chemfig{-CH_2(-[@{a}2]@{e}H)-[@{b}]CH_2(-[@{c}2]@{d}\charge{0=\:,90=\:,180=\:}{Br})-}
    \arrow
    \chemfig{-CH_2=CH_2-}
    \+
    \chemfig{HBr}
    %------------------------------------------------------------------------------------
    \chemmove[-stealth,red]{
    \draw[shorten <=1pt,shorten >=1pt](a).. controls +(0:4mm) and +(90:4mm)..(b);
    \draw[shorten <=1pt,shorten >=1pt](c).. controls +(180:4mm) and +(240:4mm)..(d);
    \draw[shorten <=3pt,shorten >=1pt](d).. controls +(180:8mm) and +(60:8mm)..(e);
    }
    \schemestop
\end{document}

Answer 2

I don't know anything about such reaction schemes, but you can add marks not only to bonds (which you do in your MWE for example using -[@{sb1}]), but also to atoms by adding such a mark in front of the relevant letter representing this atom, for example using @{sb3}H. Using these marks, you can then add arrows using \draw macros inside a \chemmove macro:

\documentclass[border=10pt]{standalone}
\usepackage{chemfig}

\begin{document}
\schemestart
\chemfig{H-C(-[2]H)([6]-[@{sb1}]@{sb3}H)-[@{sb2}]\charge{0:3pt=$\scriptstyle\oplus$}{C}(-[2]H)(-[6]H)}
\chemmove[-stealth, shorten >=2pt, shorten <=2pt, red]{
    \draw (sb1) to[out=0, in=270] (sb2);
    \draw ([shift={(10pt,-10pt)}]sb3.center) to[out=90, in=90, looseness=3.5] 
        ([shift={(-10pt,-10pt)}]sb3.center);
}
\arrow(.mid east--.mid west)
\chemfig{H-C(-[2]@{sb1}H)=C(-[2]@{sb2}H)-H}
\chemmove[-stealth, shorten >=2pt, shorten <=2pt, red]{
    \draw ([shift={(20pt,0pt)}]sb2.center) to[out=210, in=300, looseness=1.5] 
        ([shift={(-20pt,0pt)}]sb1.center);
}
\+
\chemfig{H^+}
\schemestop
\end{document}