Unsaturated Hydrocarbons

Unsaturated hydrocarbons contain carbon-carbon double or triple bonds. Unsaturated hydrocarbons having carbon-carbon double bonds (C=C) are called alkenes whereas those having carbon-carbon triple bonds (C≡C) are known as alkynes.


The simplest alkene, ethene has two carbon atoms joined by a double bond. Its molecular formula is C2H4.

Similar to alkanes, alkenes also form a homologous series of compounds in which each member differs from the next one by a -CH2 unit. The homologous series of alkenes can be represented by the general formula CnH2n where n represents the number of carbon atoms in the alkene molecule.

IUPAC Name of Alkene

Example: C2H4, Word root + ene -> eth + ene -> Ethene

The names of alkenes are given by replacing the -ane suffix of alkanes by -ene. The other rules for the nomenclature of alkenes are same as those of alkanes. However, the position of the double bond is indicated by the smaller number of the two carbon atoms forming the double bond.


The simplest alkyne is ethyne and it has molecular formula C2H2. Its common name is acetylene. It is used to ripen the fruits such as banana, mango. It is also used along with oxygen in oxy-acetylene torch which is used for welding purposes.

The general formula for the homologous series of alkynes is CnH2n-2 where n is the number of carbon atoms in the alkyne molecule.

IUPAC Name of Alkyne

Example: C2H2, Word root + yne -> eth + yne -> Ethyne

Alkynes are named by replacing -ane suffix of alkanes by -yne suffix. The other rules of nomenclature of alkynes are similar to those of alkanes.