A chain or ring of hydrocarbons containing two carbon-carbon double bonds in a molecule is called a diolefin. In terms of molecular structure, there are cyclic diolefins (e.g., 1, 3-cyclopentadiene) and chain diolefins. Generally, a diolefin is an unsaturated chain hydrocarbon with two double bonds in the molecule. In diolefin molecules, due to the different positions of the two double bonds, there are three situations: 1. Aggregation of double-bonded diolefins such as propylene CH2=C=CH2.

It's a colorless gas that, when heated, isomerizes into propyl. 2. Conjugate double bond diolefin A diolefin in which two double bonds are separated by a single bond. Examples include 1, 3-butadiene, 1, 3-pentadiene and isoprene. Conjugated diolefin has similar chemical properties with olefin, the main characteristics of 1,4 addition, polymerization reaction. 3. Isolation of double bonds Diolefin A diolefin in which two double bonds are separated by more than two single bonds. For example, 1, 4-hexadiene (CH2= ch-ch2-ch =CH -- CH3). In the diolefin, conjugated double-bonded diolefin is the most important class, in which butadiene and isoprene are important raw materials for synthetic rubber.

Clustered double-bonded diolefins are very unstable. Isolated double-bonded diolefins have essentially the same properties as monoolefins. Conjugated diolefins, in addition to their properties as monoolefins, can also undergo 1,4 -- addition, 1, 4- addition and diene synthesis reactions.