Dienes or diolefins are hydrocarbons which contain two double bonds. Dienes are intermediate between alkenes and polyenes.

[edit] Classes

Dienes can be divided into four classes:

1. Unconjugated dienes have the double bonds separated by two or more single bonds.
2. Conjugated dienes have conjugated double bonds separated by one single bond. They are also the most stable.
3. Cumulated dienes have the double bonds sharing a common atom as in a group of compounds called allenes.
4. Heterodienes have one or more of the unsaturated carbon atoms replaced with a heteroatom.

Classes of Dienes

1,5-Cyclooctadiene, an unconjugated diene. Notice that each double bond is two carbons away from the other.

Isoprene, also known as 2-methyl-1,3-butadiene, is one of the simplest conjugated dienes.

Propan-1,2-diene, also known as allene, is the simplest cumulated diene.

In organic chemistry a conjugated diene is also a functional group, with a general formula of C_nH_2n-2. A classic organic reaction for the synthesis of dienes is the Whiting reaction.

1,3-butadiene undergoes 1,2-addition and 1,4-addition.

diene is called cyclo - alkynes

[edit] Reactions with dienes

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 for example Danishefsky’s diene.

[edit] External links

• IUPACs Gold Book definition of dienes [1]