Hydrocarbons (continued)


Alkenes are acyclic and unsaturated hydrocarbons which contain a double bond between carbon atoms.

They are also called olefins, alkenes or ethylene hydrocarbons. Its general formula is ÇnoH2n

Some alkenes:

ethylene CH2 = CH2 molecular formula: C2H4

1-butene CH2= CH - CH2 - CH3 molecular formula: C4H8


Alkenes are more reactive than alkanes because they have a double bond which is easier to break. They undergo addition and also polymerization reactions.


The most common compound of alkenes is ethylene, or ethylene. It is produced in green fruits and acts in the ripening of these fruits. For this reason, we wrap the fruits with newspaper so that it ripens faster. In this way, the ethylene gas is being trapped and accelerates the ripening speed.

Ethylene is produced in the chemical industry and is obtained by refining petroleum and natural gas. It is also used for the manufacture of polyethylene used to make plastics.


To name the alkenes, we use the alkane-like nomenclature. As for the number of carbons is the same (met, et, prop, but…). As for the type of connection, we use en. However, the location of the double bond must be indicated.

To name, priority is given to double bonding in carbon counting and then to radicals. See the examples:

1) CH2 = CH - CH2 - CH3

Old nomenclature: 1- butene
IUPAC Nomenclature: but-1-eno

2) CH3 - CH = CH - CH3

Old nomenclature: 2-Butene
IUPAC Nomenclature: but-2-eno

For the alkenes branched, the (longer) main chain is the one containing the double bond. Carbon counting is done from the nearest end of the double bond. See the examples:

Old nomenclature: 5-methyl-2-hexene
IUPAC Nomenclature: 5-methylhex-2-ene

Old nomenclature: 3-propyl-1-heptene
IUPAC Nomenclature: 3-Propyl-hept-1-ene


The ethylene-derived radical is vinyl or ethenyl.

CH2 = CH -   vinyl or ethenyl