Basic Organic Nomenclature


Alkenes - Multiple Double Bonds

Family name: suffix: -ene

There are of course compounds which contain two or more double bonds. The general formulas for these alkenes are: CnH2n-2, CnH2n-4, CnH2n-6, ..., for two, three, four, ... double bonds. Again, the loss of each pair of hydrogen atoms indicates the presence of an additional double bond between two carbon atoms.

The naming of the poly-alkenes is similar to that of a simple alkene.

The presence of the multiple bonds are indicated in the name by: first, the number locating each double bond present; second, by adding the di, tri, tetra, ... prefixes before the -ene ending. NOTE: you need to add an "a" before the di, tri, etc, i.e. 1,3-butadiene, 1,3,5-hexatriene.

Examples of naming poly-alkenes are:

Compound Name
Line Drawing
3D Model
1,3-butadiene
4-methyl-1,3-pentadiene
2-methyl-1,4-pentadiene
1,3,6-heptatriene
5-methyl-1,3-cyclohexadiene

There are a number of terms used to describe the relationship of multiple double bonds to one another. The first are isolated double bonds. These occur when there are two or more single bonds between the double bonds. The second are conjugated double bonds. This occurs when there is only one single bond between the double bonds. This arrangement allows the double bonds to interact with one another, and the entire system will tend to be planar. Finally, there are what are termed cumulated double bonds. These occur when a central carbon atom forms double bonds to two carbon atoms, one on each side. This results in a linear arrangement of the three carbon atoms. For example:
 
 

Isolated Double Bond
Conjugated Double Bond
Cumulated Double Bond
NOTE: In the line drawing the space between the double bonds in the cumulated double bond indicates the central carbon atom of the two double bonds.

Tutorial Quiz: Alkenes

Next Page: Alkenes - III

Return to Index