How do you name alkenes using systematic names?
You name alkenes as you do alkanes, but with the ending ene and giving the double bond the highest numbering priority.
Find the longest continuous chain of carbon atoms that contains both carbons of the double bond.
Give the lowest possible number to the
Add substituents and their positions to the name of the alkene as prefixes.
Identify stereoisomers. It is always safest to use the Cahn-Ingold-Prélog E/Z notation.
Give a name for
We have a six-carbon chain with a double bond between
The methyl group at
Now we indicate stereochemistry.
The two higher-priority groups are the methyl group on
Since they are on opposite sides of the double bond, the configuration is E.
The full name for the compound is (E)-5-methylhex-2-ene.
(E)-5-methyl-2-hexene is an acceptable name, but the preferred name puts the numbers closest to the groups they locate.