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chemfig

chemfig draws molecules from a line of text: atoms, the bonds between them, the angles of those bonds, branches and rings. fxTeX Pro draws each one as SVG, inside the equation, so a structure can sit in a sentence or beside an arrow like any other piece of maths. The editor below has the chemistry panels — chemfig's and mhchem's — with the maths a chemist needs around them. Click any example on this page to open it there.

Adding chemfig to your page

In fxTeX Pro, name chemfig when you render the page:

fxTeXPro.ready.then(() => {
  fxTeXPro.unlock('fx_pk_your-key-here');
  fxTeXPro.autoRender({ packages: ['chemfig'] });
});

In the equation editor, name it to EqEditor.init() and add its panels to the toolbar. This is the editor above, with mhchem as well:

<script src="https://fxeditor.codecogs.com/fxeditor.api.min.js"></script>

<div id="toolbar"></div>
<div id="mathview"></div>
<div id="latex"></div>

<script>
  const ready = EqEditor.init({
    licence: 'fx_pk_your-key-here',
    packages: ['mhchem', 'chemfig']
  });

  const toolbar = EqEditor.Toolbar.link('toolbar', [
    ['mhchem', 'mhchem_arrows', 'chemfig', 'chemfig_ext', 'arrows'],
    ['operators_core', 'subsupset', 'brackets', 'greeklower', 'greekupper', 'symbols', 'spaces']
  ]);

  ready.then(() => {
    const latex = EqEditor.LaTeXView.link('latex');
    const mathview = EqEditor.MathView.link('mathview').addLaTeXView(latex);
    toolbar.addLaTeXView(latex).addMathView(mathview);
    mathview.setLatex('\\chemfig{H_3C-C(=[1]O)-[7]OH}');
  });
</script>

The chemfig panel has rings, bonds, bond angles and branches, and writes inside \chemfig{} — adding it only when the caret is not in one already, so each button extends the molecule you are drawing. chemfig_ext has charges, lone pairs, names, brackets and reaction schemes. chemfig is the largest of the packages, 112 kB gzipped: name it only on the pages that use it. See Using packages for more on both steps.

Atoms and bonds

Atoms are letters, with subscripts as in maths; bonds are the symbols between them.

\chemfig{A-B}

A B

Single bond.

\chemfig{A=B}

A B

Double bond.

\chemfig{A~B}

A B

Triple bond.

\chemfig{A>B}

A B

Wedge: towards the viewer.

\chemfig{A<B}

A B

Wedge the other way.

\chemfig{A>:B}

A B

Hashed wedge: away from the viewer.

\chemfig{A>|B}

A B

Hollow wedge.

\chemfig{CH_3-CH_2-OH}

C H 3 C H 2 O H

Ethanol: groups of atoms, with subscripts.

Bond angles

A bond goes to the right unless told otherwise, in square brackets after it: a number n on its own is n×45°, :30 is an absolute angle in degrees, and ::30 is relative to the bond before.

\chemfig{A-[1]B}

A B

45°.

\chemfig{A-[2]B}

A B

90°, straight up.

\chemfig{A-[7]B}

A B

315°, down to the right.

\chemfig{A-[:30]B}

A B

30°, absolute.

\chemfig{A-[::30]B-[::30]C}

A B C

30° on from the bond before, each time.

\chemfig{A-[,2]B}

A B

The second option is the bond's length: twice as long.

\chemfig{-[:30]-[:-30]-[:30]-[:-30]}

A skeletal chain: bonds with no atoms.

Branches

A bond in round brackets after an atom is a branch off it; the chain carries on after the bracket.

\chemfig{H-C(-[2]H)(-[6]H)-H}

H C H H H

Methane, with branches up and down.

\chemfig{H_3C-C(=[1]O)-[7]OH}

H 3 C C O O H

Acetic acid.

\chemfig{H-C(-[2]H)(-[6]H)-C(=[1]O)-[7]H}

H C H H C O H

Acetaldehyde.

Rings

*6(...) is a ring of six, with its bonds in the brackets; **6 draws a circle inside it. Anything in brackets on a ring's atom is a substituent, and a ring can be one.

\chemfig{*6(-=-=-=)}

Benzene, with alternating double bonds.

\chemfig{**6(------)}

Benzene, with a circle.

\chemfig{*6(------)}

Cyclohexane.

\chemfig{*5(-----)}

A five-membered ring.

\chemfig{CH_2*3(-CH_2-CH_2-)}

C H 2 C H 2 C H 2

Cyclopropane, with its atoms named.

\chemfig{*6(-=-(-OH)=-=)}

O H

Phenol: a substituent on the ring.

\chemfig{*6(=-*6(-=-=-)=-=-)}

Naphthalene: a ring fused to a ring.

\chemfig{[:-30]*6(-=-=-=)}

The whole molecule turned 30°.

Charges and lone pairs

\charge puts something beside an atom at an angle; \: is a lone pair. \chemabove and \chembelow put it above or below.

\chemfig{\charge{90=\:,270=\:}{O}}

O

Lone pairs above and below.

\chemfig{\Charge{45=$\scriptstyle\oplus$}{N}}

N ⊕

\Charge sets it a little further out.

\chemfig{\chemabove{N}{\oplus}(-[2]H)(-[6]H)-H}

N ⊕ H H H

A charge above an atom, with branches.

\chemfig{H_3\chemabove{N}{\oplus}-CH_2-COO^{\ominus}}

H 3 N ⊕ C H 2 C O O ⊖

Glycine as a zwitterion.

\setcharge{circle}\chemfig{\charge{90=+}{N}}

N +

\setcharge styles every charge after it.

Names and brackets

\chemname{\chemfig{*6(=-=-=-)}}{Benzene}

B e n z e n e

\chemname sets a name under a molecule.

\chemleft[\chemfig{A-B}\chemright]^{\ominus}

{[A B]}^{⊖}

Brackets sized to the molecule, with a charge.

Reaction schemes

Between \schemestart and \schemestop, \arrow joins whatever is either side of it: text, or molecules. Its type goes in braces, with labels in square brackets above and below; \+ is a plus.

\schemestart A \arrow B \arrow C \schemestop

A B C

A sequence.

\schemestart A \+ B \arrow C \schemestop

A + B C

Two reactants.

\schemestart A \arrow{<=>} B \schemestop

A B

Equilibrium.

\schemestart A \arrow{<->} B \schemestop

A B

Resonance.

\schemestart A \arrow{-/>} B \schemestop

A B

No reaction.

\schemestart A \arrow{->[a][b]} B \schemestop

A a b B

Labels above and below.

\schemestart \chemfig{*6(-=-=-=)} \arrow{->[\chemfig{Br_2}][\chemfig{FeBr_3}]} \chemfig{*6(-=-=(-Br)-=)} \schemestop

B r 2 F e B r 3 B r

The bromination of benzene.

Settings and shortcuts

Options in square brackets after \chemfig apply to that molecule; \setchemfig sets them for every one after it. \definesubmol names a piece of a molecule, to use again with !{name}.

\chemfig[atom sep=2em]{A-B-C}

A B C

Shorter bonds, for this molecule.

\setchemfig{atom sep=3em}\chemfig{A-B}

A B

For every molecule after it.

\chemfig{A-[,,,,red]B}

A B

The fifth bond option styles it.

\definesubmol{x}{-[:30]-[:-30]}\chemfig{A!{x}!{x}B}

A B

A piece defined once, used twice.

The chemfig manual

This page covers the parts of chemfig used most. chemfig itself is by Christian Tellechea; its manual has every option, and many more molecules:

chemfig manual (PDF) — the LaTeX package's documentation, in English, on CTAN.

chemfig on CTAN — the package, its licence, and the manual in French.

mhchem — chemical formulae, equations and units.

Using packages — turning packages on, and their panels.

Supported commands — every chemistry command fxTeX reads.

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