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I have decided to mark down the mechanism that I have learnt. However, I have got some problem. I would like to use a vertical arrow on the second step but I do not know any command that can form a vertical arrow. Also, I would like to ask why part of my command does not count as command in the question part?

\documentclass[12pt,a4paper]{report}

\usepackage{chemfig}

\usepackage[version=4]{mhchem}

\begin{document}

\title{mechanism}

\maketitle

\newpage

\section*{addition of hydrogen halide to alkene}

\begin{center}
    
\schemestart
    \chemfig{-[:-60]C(-[:240])=_[@{a1}]C(-[:60])(-[:-60])}
    \arrow{0}[,0]\+
    \chemfig{@{a2}H-[@{a3}]@{b1}X@{z}}
    \arrow(.mid east--.mid west)
    \chemfig{-C(-[:90]H)(-[:-90])-@{b2}\chemabove{C}{\oplus}(-[:-90])(-)}
    \arrow{0}[,0]\+
    \chemfig{@{b3}\charge{180=\:}{X}\chemright{X}{\ominus}}
    \schemestop
    \chemmove{
        \draw(a1)..controls +(100:5mm) and +(145:5mm)..(a2);
        \draw(a3)..controls +(100:5mm) and +(145:5mm).. (b1);
        \draw(b3)..controls +(100:5mm) and +(45:5mm).. (b2);
    }

\end{center}

\end{document}

enter image description here

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  • Also, could you please help me to amend the b3 to b2 arrow also? I would like to have the arrow drawn from the lone pair of electron to the carbocation. Thank you.
    – some one
    Jan 7, 2022 at 3:08
  • Forget to mention, I would like to have the vertical arrow point from the + in second step. Thank you.
    – some one
    Jan 7, 2022 at 3:25
  • Tip: Don't add requirements as comments, instead, edit the question. Jan 7, 2022 at 3:39
  • Vertical arrows are drawn with A\arrow[90]B
    – Roland
    Jan 7, 2022 at 3:42

2 Answers 2

2

As mentioned in the comment vertical arrows are drawn with A\arrow[90]B.

In order to arrange the arrow to the plus sign see example below:

\documentclass[border=1cm]{standalone}

\usepackage{chemfig}


\begin{document}    
    
    \schemestart
    A\subscheme{\+}BCDEF \arrow G
    \arrow(@c2--)[-90]H
    \schemestop
    
\end{document}

enter image description here

Taken together in your code:

\documentclass[12pt,a4paper]{report}

\usepackage{chemfig}

\usepackage[version=4]{mhchem}

\begin{document}
    
    \title{mechanism}
    
    \maketitle
    
    \newpage
    
    \section*{addition of hydrogen halide to alkene}
    
    \begin{center}
        
        \schemestart
        \chemfig{-[:-60]C(-[:240])=_[@{a1}]C(-[:60])(-[:-60])}
        \arrow{0}[,0]\+
        \chemfig{@{a2}H-[@{a3}]@{b1}X@{z}}
        \arrow
        \chemfig{-C(-[:90]H)(-[:-90])-@{b2}\chemabove{C}{\oplus}(-[:-90])(-)}
        \arrow{0}[,0]\subscheme{\+}
        \chemfig{@{b3}\charge{180=\:}{X}\chemright{X}{\ominus}}
        \arrow(@c5--)[-90]
        \chemfig{-C(-[:90]H)(-[:-90])-C(-[:90]Y)(-[:-90])-}
        \schemestop
        \chemmove{
            \draw(a1)..controls +(100:5mm) and +(145:5mm)..(a2);
            \draw(a3)..controls +(100:5mm) and +(145:5mm).. (b1);
            \draw(b3)..controls +(100:5mm) and +(45:5mm).. (b2);
        }
        
    \end{center}
    
\end{document}

enter image description here

1
  • @some one If my answer solved your problem you might consider to accept it.
    – Roland
    Jan 7, 2022 at 5:08
0

Do you want something like this? Using \subscheme helps position the arrow in the center of each reaction step.

\begin{center}
        
        \schemestart
%
        \subscheme{
        \chemfig{-[:-60]C(-[:240])=_[@{a1}]C(-[:60])(-[:-60])}
        \arrow{0}[,0]\+
        \chemfig{@{a2}H-[@{a3}]@{b1}X@{z}}
        }
%
        \arrow{->}[270,1]
%
        \subscheme{
        \chemfig{-C(-[:90]H)(-[:-90])-@{b2}\chemabove{C}{\oplus}(-[:-90])(-)}
        \arrow{0}[,0]\+
        \chemfig{@{b3}\charge{90:1pt=\:,45:3pt=$\ominus$}{X}}
        }
%
\arrow{->}[270,1]
%
        \chemfig{C(-[2]H)(-[4])(-[6])-C(-[2]X)(-[0])(-[6])}
        \schemestop
        \chemmove{
            \draw[red,shorten <=1pt,shorten >=1pt](a1)..controls +(100:5mm) and +(145:5mm)..(a2);
            \draw[red,shorten <=1pt,shorten >=1pt](a3)..controls +(100:5mm) and +(145:5mm).. (b1);
            \draw[red,shorten <=3pt,shorten >=1pt](b3)..controls +(90:8mm) and +(45:8mm).. (b2);
        }
        
    \end{center}

enter image description here

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