Dienes are hydrocarbons which contain two double bonds.

Classes

Dienes can divided into three classes:

1. Unconjugated dienes have the double bonds separated by two or more single bonds.
2. Conjugated dienes have the double bonds separated by one single bond.
3. Cumulated dienes have the double bonds sharing a common atom.

Common examples

The simplest conjugated diene is 1,3-butadiene:

The 1,3 configuration of double bonds found in 1,3-butadiene (conjugated double bonds) make these types of dienes capable of participating in more reaction types than is the case for molecules with either just a single alkene functional group or with multiple, but non-alternating, alkene groups. One possible reaction for such dienes is the Diels-Alder reaction.

A compound in which two double bonds exist but are immediate adjacent to each other is, in contrast, called an allene.

Cyclopentadiene is another example of a diene.