How do I align a set of chemical formulae

Question

Here's the image I want to recreate -

Here's my attempt at recreating it -

\documentclass{12pt}{book}
\usepackage{amsmath, amssymb}
\usepackage{mhchem}
\usepackage{graphicx}
\usepackage{tikz}
\begin{document}
\begin{align}
    \ce{Cl^{.} + CH4 -> CH3^{.} + HCl} \
    \ce{CH3^{.} + Cl2 -> CH3Cl + Cl^{.}} \ \
    \ce{Cl^{.} + CH4 -> CH3^{.} + HCl} \
    \ce{CH3^{.} + Cl2 -> CH3Cl + Cl^{.}} \ \
    \ce{Cl^{.} + CH4 -> CH3^{.} + HCl} \
    \ce{CH3^{.} + Cl2 -> CH3Cl + Cl^{.}}
\end{align}
\end{document}

this yields -

Any ideas on how I can insert the red circles and lines?

I only know how to align it along the arrows; you just insert & before each symbol -> but for dots mhchem package seems to be using . or * for dots next to chemical symbols and typeset them in the middle — Celdor, Sep 22 '22 at 15:58

score 0 · Answer 1 · answered Sep 22 '22 at 16:29

So I checked the package mhchem. It seems adding * or . next to a symbol generates a dot with vertical alignment with respect to a symbol. It seems to do what you are looking for.

For the alignment, use & as a separator around which LaTeX will align left and right parts (see my previous comments on a similar problem: here and here or wiki about alignat or align).

\documentclass[12pt]{book}
\usepackage{amsmath, amssymb}
\usepackage{mhchem}
\usepackage{graphicx}
\usepackage{tikz}
\numberwithin{figure}{chapter}
\begin{document}
\chapter{Sample chapter}
\begin{figure}[htb]
  \begin{alignat}{3}
    \ce{  & Cl + CH4  &->&* && CH3 + HCl} \
    \ce{* & CH3 + Cl2  &->&  && CH3Cl + Cl} \[12pt]
    \ce{  & Cl + CH4  &->&* && CH3 + HCl} \
    \ce{* & CH3 + Cl2  &->&  && CH3Cl + Cl} \[12pt]
    \ce{  & Cl + CH4  &->&* && CH3 + HCl} \
    \ce{* & CH3 + Cl2  &->&  && CH3Cl + Cl}
  \end{alignat}
  \caption{The propagation step is repeated over again and again.}\label{fig:propagation}
\end{figure}
\end{document}

CrocoDuck · Accepted Answer · 2022-09-22T18:23:56.177

I did something similar using "chemfig"

\documentclass[border={4mm}]{standalone}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{chemfig}
\usepackage{tikz}
\newenvironment{f}{$\displaystyle\aligned}{\endaligned$}
\begin{document}
\begin{f}
&\schemestart
\chemfig{@{a}\charge{0=.}{C\ell}} + \chemfig{CH_4}  \arrow{->} \chemfig{\charge{0=.}{CH_3}} + \chemfig{HC\ell}
\schemestop
\
%
& \schemestart
%
\chemfig{\charge{180=.}{CH_3}} + \chemfig{C\ell_2} \arrow{->} \chemfig{CH_3C\ell} + \chemfig{@{b}\charge{0=.}{C\ell}}
\schemestop
\ \
&\schemestart
\chemfig{@{c}\charge{0=.}{C\ell}} + \chemfig{CH_4}  \arrow{->} \chemfig{\charge{0=.}{CH_3}} + \chemfig{HC\ell}
\schemestop
\
%
& \schemestart
%
\chemfig{\charge{180=.}{CH_3}} + \chemfig{C\ell_2} \arrow{->} \chemfig{CH_3C\ell} + \chemfig{@{d}\charge{0=.}{C\ell}}
\schemestop
\ \
&\schemestart
\chemfig{@{e}\charge{0=.}{C\ell}} + \chemfig{CH_4}  \arrow{->} \chemfig{\charge{0=.}{CH_3}} + \chemfig{HC\ell}
\schemestop
\
%
& \schemestart
%
\chemfig{\charge{180=.}{CH_3}} + \chemfig{C\ell_2} \arrow{->} \chemfig{CH_3C\ell} + \chemfig{@{f}\charge{0=.}{C\ell}}
\schemestop
\ \
    % myedge={right}   para meia seta

%\begin{tikzpicture}
    \chemmove{
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,shorten <=6pt,shorten >=6pt.. controls +(240:16mm) and +(60:16mm)..(c);
    \drawred,shorten <=6pt,shorten >=6pt.. controls +(240:16mm) and +(60:16mm)..(e);
}
\end{f}
\end{document}

this code will align the arrows

\documentclass[border={4mm}]{standalone}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{chemfig}
\usepackage{tikz}
\newenvironment{f}{$\displaystyle\aligned}{\endaligned$}
\begin{document}
\begin{f}
\schemestart
\chemfig{@{a}\charge{0=.}{C\ell}} + \chemfig{CH_4} \schemestop  & \schemestart \arrow{->} \chemfig{\charge{0=.}{CH_3}} + \chemfig{HC\ell}
\schemestop
\
%
\schemestart
%
\chemfig{\charge{180=.}{CH_3}} + \chemfig{C\ell_2} \schemestop & \schemestart \arrow{->} \chemfig{CH_3C\ell} + \chemfig{@{b}\charge{0=.}{C\ell}}
\schemestop
\ \
\schemestart
\chemfig{@{c}\charge{0=.}{C\ell}} + \chemfig{CH_4}\schemestop   & \schemestart \arrow{->} \chemfig{\charge{0=.}{CH_3}} + \chemfig{HC\ell}
\schemestop
\
%
 \schemestart
%
\chemfig{\charge{180=.}{CH_3}} + \chemfig{C\ell_2}\schemestop &  \schemestart \arrow{->} \chemfig{CH_3C\ell} + \chemfig{@{d}\charge{0=.}{C\ell}}
\schemestop
\ \
\schemestart
\chemfig{@{e}\charge{0=.}{C\ell}} + \chemfig{CH_4} \schemestop &\schemestart \arrow{->} \chemfig{\charge{0=.}{CH_3}} + \chemfig{HC\ell}
\schemestop
\
%
\schemestart
%
\chemfig{\charge{180=.}{CH_3}} + \chemfig{C\ell_2} \schemestop & \schemestart \arrow{->} \chemfig{CH_3C\ell} + \chemfig{@{f}\charge{0=.}{C\ell}}
\schemestop
%------------------------------------------------------
    \chemmove{
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,dotted circle (.35);
    \drawred,shorten <=6pt,shorten >=6pt.. controls +(240:16mm) and +(60:16mm)..(c);
    \drawred,shorten <=6pt,shorten >=6pt.. controls +(240:16mm) and +(60:16mm)..(e);
}
\end{f}
\end{document}

How do I align a set of chemical formulae

2 Answers2