Drawing Benzene resonance mechanism, and reaction mechanism + curly arrows

Question

I am new to LaTeX and there are few things at which I am stuck.

I can draw benzene with alternate double bonds but I don't know how to draw curly arrows to show bond shifting and electrophile attack.

I would like to show reaction mechanism of benzene like this:

_{(source: chemguide.co.uk)}

_{(source: chemguide.co.uk)}

and

_{(source: ucla.edu)}

EDIT

There is one another thing I need an expert opinion. I wanted to show covalent bonding in comparison with excited and grounded state of electron. This is the code that I have written. Is there any better way to show Cl sharing its electron than what I have done (adding lots of space in my opinion is not a best way)?

And is possible to draw a curly arrow from the second box to the third to show that an electron is given energy to go to a higher energy level?

\documentclass [11pt] {book}
\usepackage[utf8x]{inputenc}
\usepackage{ucs}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{chemfig}
\usepackage{tikz}
\begin{document}
$_4$Be~: 1s$^2$~2s$^2$
\\
\\
Ground State:
\begin{tabular}{|c|}
\hline $\upharpoonleft$$\downharpoonright$ \\ 
\hline 
\end{tabular} 
\begin{tabular}{|c|}
\hline $\upharpoonleft$$\downharpoonright$ \\ 
\hline 
\end{tabular} 
\begin{tabular}{|c|c|c|}
\hline ~~~&~~~&~~~\\ 
\hline 
\end{tabular} 
\\
\\
Excited State:\begin{tabular}{|c|}
\hline $\upharpoonleft$$\downharpoonright$ \\ 
\hline 
\end{tabular} 
\begin{tabular}{|c|}
\hline $\upharpoonleft$~ \\ 
\hline 
\end{tabular} 
\begin{tabular}{|c|c|c|}
\hline $\upharpoonleft$~~&~~~&~~~\\ 
\hline 
\end{tabular} 

~~~~~~~~~~~~~~~~~~~~~~~~$\uparrow$~~~~~$\uparrow$

~~~~~~~~~~~~~~~~~~~~~~~Cl~~~~Cl

\end{document}

Answer 1

chemfig allows to add explizit node names to either bonds or atoms in its formulae by using the @{<name>} syntax. These names can be used in a tikzpicture with the options remember picture, overlay to draw the curved arrows. chemfig provides the wrapper \chemmove for this. So a combination of chemfig and TikZ can be used to draw the schemes. (BTW: the chemfig manual actually has quite a few examples of such schemes...)

Here is something that might get you started:

\documentclass{article}
\usepackage{chemfig}
\tikzset{
  elmove/.style={->,shorten >=3pt, shorten <=3pt}
}
\begin{document}

\schemestart
  \chemfig{*8(-[@{sb1}]=[@{db1}]-[@{sb2}]=[@{db2}]-[@{sb3}]=[@{db3}]-[@{sb4}]=[@{db4}])}
  \arrow{<->}
  \chemfig{*8(=-=-=-=-)}
\schemestop
\chemmove[red,elmove]{
  \draw (db1) .. controls  +(90:5mm) and  +(45:5mm) .. (sb1) ;
  \draw (db2) .. controls +(180:5mm) and +(135:5mm) .. (sb2) ;
  \draw (db3) .. controls +(270:5mm) and +(225:5mm) .. (sb3) ;
  \draw (db4) .. controls   +(0:5mm) and +(315:5mm) .. (sb4) ;
  % similar the others
}

\bigskip

\schemestart
  \chemfig{**6(----[@{b}]--)}
  \arrow(benzene.base east--.base west){->[][][15pt]}
  \chemfig{**[120,420,dashed]6(---(-[,-1,,,draw=none]{+})-(-[:120]H)(-[:60]NO_2)--)}
  \arrow(@benzene.45--){0}[45,.2]
  \chemfig{@{N}\chemabove{N}{+}O_2}
\schemestop
\chemmove[blue,elmove]{
  \draw[shorten <=-5pt] (b) .. controls +(30:5mm) and +(-90:1cm) .. (N) ;
}

\end{document}

---

My package modiagram can be used to draw the electronic state diagram. IMHO It doesn't fit perfectly and a TikZ-only solution may be preferable. On the other hand the code is rather easy:

\documentclass[11pt]{book}
\usepackage[utf8]{inputenc}
\usepackage{chemformula,modiagram,chemfig}

% necessary due to stupid bug in `modiagram':
\newcommand*\makecolonother{\catcode`\:=12 }

\begin{document}
\ch{_4Be}: 1s$^2$~2s$^2$

ground state:
\begin{MOdiagram}[style=square,AO-width=8pt]
  \AO(0pt){s}{0;pair}
  \AO(12pt){s}{0;pair}
  \AO(24pt){s}{0;}
  \AO(34pt){s}{0;}
  \AO(44pt){s}{0;}
  \draw[overlay,red,->]
    (AO2.north) .. controls +(0,.5) and +(0,.5) .. (AO3.north) ;
\end{MOdiagram}

excited state:
\begin{MOdiagram}[style=square,AO-width=8pt]
  \AO(0pt){s}{0;pair}
  \AO(12pt){s}{0;up}
  \AO(24pt){s}{0;up}
  \AO(34pt){s}{0;}
  \AO(44pt){s}{0;}
  \makecolonother
  \draw[<-,overlay]
    (AO2.south) -- ++(-100:3mm) node[below] {Cl} ;
  \draw[<-,overlay]
    (AO3.south) -- ++(-80:3mm) node[below] {Cl} ;
\end{MOdiagram}

\end{document}