# Chemistry formulae

There are a few LaTeX packages to create chemistry formulae: chemfig, ochem, streetex, and xymtex. The most intuitive is probably the ** chemfig** package. This article explains how to use the

**chemfig**package to create chemical formulas in LaTeX.

## Introduction

Drawing a molecule consists mainly of connecting groups of atoms with lines. Simple linear formulas can be easily drawn with **chemfig**, let's see:

```
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{chemfig}
\section{Introduction}
Writting chemical formulae with chemfig is straightforward.
\chemfig{O=H}
\end{document}
```

The package is imported by ** \usepackage{chemfig}** in the preamble. The command

`\chemfig{O=H}`

the draws the molecule. The symbol `=`

determines the type of bond. See the reference guide for a list of bond types.
Open an example of the chemfig package in ShareLaTeX

## Angles

There are several ways to define angles to draw the bonds between molecules.

```
To define chemical formulae you can use units that define the angles
\chemfig{A-[1]B-[7]C}
Absolute angles
\chemfig{A-[:50]B-[:-25]C}
Relative angles
\chemfig{A-[::50]B-[::-25]C}
```

Each one of the three commands in the example above uses a different method to determine the angle between bonds.

In the command**default units**`\chemfig{A-[1]B-[7]C}`

the parameters inside brackets set the angle in special units, each unit equals 45°. Hence in the example the angles are 45° and 315°.The angles can be set in absolute units, in the command**absolute units**`\chemfig{A-[:50]B-[:-25]C}`

the parameter inside the brackets represent the angle, in degrees, measured from the horizontal baseline. Negative angles are allowed.In the third example**relative angles**`\chemfig{A-[::50]B-[::-25]C}`

the angles are measured from the previous bond, instead of the baseline.

Open an example of the chemfig package in ShareLaTeX

## Rings

The example below presents the syntax to draw regular polygons

The syntax of the command `\chemfig{A*5(-B=C-D-E=)}`

is explained below:

`A`

- This is the first atom, the rest of the atoms will be drawn from here

`*5`

- Number of sides of the polygon

`(-B=C-D-E=)`

- The rest of the atoms and bonds. If not enough are passed to complete the polygon, an incomplete ring will be drawn.

There is an additional parameter that can be passed to this command, a double asterisk. For instance, if "**5" is set instead of "*5" a circle is drawn inside the polygon.

Open an example of the chemfig package in ShareLaTeX

## Branches

Chemical formulas are not always linear, branched formulas are actually the most common type. Below an example on how to create them.

Branches in each node are created by adding formulas inside parentheses. For instance, the code

```
C(-[2]H)(-[6]H)
```

creates two branches in "C", one with a 2 units angle (90°) and other with a 6 units angle (270°).

Branches can also be added to rings

The syntax is similar, using parentheses a branch can be attached to a node (atom). For instance

```
F(=G)
```

attaches a branch to the node "F". More complex examples can be created using nested branches and even attaching rings as branches.

Open an example of the chemfig package in ShareLaTeX

## Customizing the formulas

Several parameters such as colours and the node separation can be changed, also additional text to describe the formula can be added.

```
{\huge
\setbondstyle{red,line width=2pt,dash pattern=on 2pt off 2pt}
\setatomsep{2em}
\chemname
{\chemfig{H-C(-[2]H)(-[6]H)-C(=[1]O)-[7]H}}
{Ethanal}
}
```

There are three new command here:

`\setbondstyle{ }`

- Inside the braces several style-related commands can be passed using the
**tikz**syntax.

`\setatomstep{2em}`

- The separation between atoms (nodes) in the formula is set to 2em. Other LaTeX units can be used.

`\chemname{}{}`

- The first parameter in this command is a
**chemfig**formula, the second one is some text that will be printed below the formula. In the example the text is "Ethanal".

Notice also that the font used is `huge`

. You can use any other font size and the formula will be scaled accordingly.

Open an example of the chemfig package in ShareLaTeX

## Reference guide

**Bond types**

## Further reading

For more information see

## Overleaf guides

- Creating a document in Overleaf
- Uploading a project
- Copying a project
- Creating a project from a template
- Including images in Overleaf
- Exporting your work from Overleaf
- Working offline in Overleaf
- Using Track Changes in Overleaf
- Using bibliographies in Overleaf
- Sharing your work with others
- Debugging Compilation timeout errors
- How-to guides

## LaTeX Basics

- Creating your first LaTeX document
- Choosing a LaTeX Compiler
- Paragraphs and new lines
- Bold, italics and underlining
- Lists
- Errors

## Mathematics

- Mathematical expressions
- Subscripts and superscripts
- Brackets and Parentheses
- Fractions and Binomials
- Aligning Equations
- Operators
- Spacing in math mode
- Integrals, sums and limits
- Display style in math mode
- List of Greek letters and math symbols
- Mathematical fonts

## Figures and tables

- Inserting Images
- Tables
- Positioning Images and Tables
- Lists of Tables and Figures
- Drawing Diagrams Directly in LaTeX
- TikZ package

## References and Citations

- Bibliography management in LaTeX
- Bibliography management with biblatex
- Biblatex bibliography styles
- Biblatex citation styles
- Bibliography management with natbib
- Natbib bibliography styles
- Natbib citation styles
- Bibliography management with bibtex
- Bibtex bibliography styles

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## Document structure

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## Formatting

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- Using colours in LaTeX
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## Fonts

## Presentations

## Commands

## Field specific

- Theorems and proofs
- Chemistry formulae
- Feynman diagrams
- Molecular orbital diagrams
- Chess notation
- Knitting patterns
- CircuiTikz package
- Pgfplots package
- Typing exams in LaTeX
- Knitr
- Attribute Value Matrices

## Class files

- Understanding packages and class files
- List of packages and class files
- Writing your own package
- Writing your own class
- Tips