Naming Alkene Cis and Trans Isomers
Name each alkene and specify its configuration by indicating cis or trans where appropriate.
Strategy
For alkenes that show cis-trans isomerism, use the designator cis to show that the carbon atoms of the of the parent chain are on the same side of the double bond, and trans to show that they are on opposite sides of the double bond.
(a) The chain contains seven carbon atoms and is numbered from the right to give the lower number to the fi rst carbon of the double bond. The carbon atoms of the parent chain are on opposite sides of the double bond. This alkene is trans-3-heptene.
(b) The longest chain contains seven carbon atoms and is numbered from the right so that the fi rst carbon of the double bond is carbon 3 of the chain. The carbon atoms of the parent chain are on the same side of the double bond. This alkene is cis-4-methyl-3-heptene.