Concept:For alkenes, select the longest carbon chain that contains the double bond, then number the chain so that the double bond receives the lowest possible locant.
Explanation:The longest chain containing the
C=C bond has five carbon atoms, so the parent name is pentene.
Numbering from the end nearer the double bond places the double bond at carbon 1.
Thus, the alkene part is named pent-1-ene.
A methyl group,
−CH3, is attached at carbon 4.
So the IUPAC name is 4-methylpent-1-ene.
The alternative numbering that would give 2-methylpent-4-ene is rejected because the double bond must have the lower locant, 1 instead of 4.
Answer:A. 4-methylpent-1-ene
