Alkenes

• Alkenes (also called olefins) contains at least one carbon-carbon double bond. Alkenes have the general formula CnH2n, where n = 2, 3, . . . . The simplest alkene is C2H4

 

Alkene Nomenclature

 

• In naming alkenes we indicate the positions of the carbon-carbon double bonds. The names of compounds containing C=C bonds end with –ene. As with the alkanes, the name of the parent compound is determined by the number of carbon atoms in the longest chain. As shown here.­­

 

 

 

 

 

 

 

 

• The number in the names of alkenes refer to the lowest numbered carbon atom in the chain that is part of the C=C bond of the alkene. The name “butene” means that there are four carbon atoms in the longest chain. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

• Both these compounds have double bonds, making them alkenes. In example (1) the longest chain consists of six carbons, so the root name of this compound will be hexene. Three methyl substituents (colored red) are present. Numbering the six-carbon chain begins at the end nearest the double bond (the left end), so the methyl groups are located on carbons 2 & 5. The IUPAC name is therefore: 2,5,5-trimethyl-2-hexene.

 

• In example (2) the longest chain incorporating both carbon atoms of the double bond has a length of five. There is a seven-carbon chain, but it contains only one of the double bond carbon atoms. Consequently, the root name of this compound will be pentene. There is a propyl substituent on the inside double bond carbon atom (#2), so the IUPAC name is: 2-propyl-1-pentene.

 

 

 

 

 

 

Source and References: Chemistry 10th edition by Raymond Chang

 

 

Written By: Glenn Malaca