Skeletal formulae

In a skeletal formula, all the hydrogen atoms are removed from carbon chains, leaving just a carbon skeleton with functional groups attached to it. For example, we've just been talking about butan-2-ol. The normal structural formula and the skeletal formula look like this:

In a skeletal diagram of this sort

• there is a carbon atom at each junction between bonds in a chain and at the end of each bond (unless there is something else there already - like the -OH group in the example);

• there are enough hydrogen atoms attached to each carbon to make the total number of bonds on that carbon up to 4.

Beware! Diagrams of this sort take practice to interpret correctly - and may well not be acceptable to your examiners (see below).

There are, however, some very common cases where they are frequently used. These cases involve rings of carbon atoms which are surprisingly awkward to draw tidily in a normal structural formula. Cyclohexane, C₆H₁₂, is a ring of carbon atoms each with two hydrogens attached. This is what it looks like in both a structural formula and a skeletal formula.

And this is cyclohexene, which is similar but contains a double bond:

But the commonest of all is the benzene ring, C₆H₆, which has a special symbol of its own.