 Another special class of hydrocarbons are known as the aromatics. We're not going to go into these in great depth in this course, but it's worth knowing a little about them. Firstly, they're called aromatics because they generally have a distinctive smell. However, there are many organic molecules with distinctive smells that are not aromatic hydrocarbons, so in that sense the name is a bit misleading. Instead, the key feature of an aromatic molecule is the pattern of alternating single and double bonds in a ring of six carbons. The simplest aromatic is this, C6H6, and it's called benzene. Benzene's a liquid and it's a minor component of petrol. Aromatics are known by historical rather than systematic names, but note that the suffix of the name is still ene, indicating the presence of double bonds. If two benzene rings are joined like this, it's called naphthalene. This is the solid white substance that's the main component of mothballs. Another ring joined on and the compound is now called anthracene. This compound is fluorescent and with some modifications it forms the basis for a large number of fluorescent dyes. If benzene rings are joined on to each other indefinitely, you eventually end up with a 2D sheet of carbon hexagons. Now where have you heard of that before? Ah yes, it's graphene, which is the layers that are stacked together to make graphite. Thank you for watching.