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

enter image description here

enter image description here

enter image description here

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}
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  • Seems you are copying certain reaction mechanisms and using the arrows to show the leaving groups and the re-ordering of the electrons involved. Can you describe what reaction mechanism / reaction your scheme should contain?
    – alchemist
    Commented Apr 5, 2023 at 10:47

2 Answers 2

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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}

enter image description here

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}

enter image description here

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  • 1
    Jasper Habicht This is an answer thanks a lot.🌹🌹🌹 Commented Apr 5, 2023 at 12:38
  • I do know about reaction schemes and chemistry .. ;-P . I find it rather odd to draw an arrow around that hydrogen atom in the carbonium ion (and here in ethene too). Arrows are used to describe movement of electron pairs (like the one in between the H and C) and/or the result of a reaction. In this example both types of arrows are used. To emphasise the leaving H-atom it could be colored, circled or printed bold instead of drawing that arrow around it.
    – alchemist
    Commented Apr 5, 2023 at 14:12

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