tools on a wooden worktop

Tools of the trade: understanding chemical structures

There are so many organic compounds because carbon likes to form bonds to lots of elements. It has four outer electrons, which it likes to share.

carbonelectrons

For example, in methane (which has the molecular formula CH4), a carbon atom shares its four electrons with four hydrogen atoms – as shown in this dot and cross diagram.

Each of the shared pairs of electrons is called a covalent bond. A covalent bond is typically represented by a straight line as shown by the full structural formula for methane.

dotandcross

Carbon also likes to share electrons with other carbon atoms and, in ethane, we see two carbon atoms share electrons to form a carbon‐carbon bond.

ethane

In ethanol we see that carbon can form a covalent bond to oxygen.

ethanol

In propanone, or acetone, we see that carbon can also form two bonds to the same oxygen atom. This carbon‐oxygen double bond is called a carbonyl group.

propanone

For larger organic compounds, drawing all of the bonds, and all of the atoms can be unwieldy – in condensed structural formula all of the atoms are shown but many, if not all, of the bonds are not included, as shown here for butanal.

butanal

The simplest way to represent organic compounds is to use skeletal structures. Each line has a carbon atom at each end, unless a different atom such as oxygen is shown, as for butanal. The end of the line stands for a carbon atom bonded to three hydrogen atoms – this is called a methyl group, sometimes abbreviated as Me.

You will notice that the carbon chain in butanal is drawn as a zig‐zag, this is because it shows the approximate shape – the shape of organic compounds is important because, as we will see, it affects their properties.

For a copy of the chemistry images (as pdfs) on this page, see below - this is a general feature of the course content and so you will be able to download the images as you work through the sections.


If you would like some further information on drawing organic structures you may find this YouTube clip of use.

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This article is from the free online course:

Exploring Everyday Chemistry

University of York