Concept:For naming an alkene, select the longest carbon chain containing the double bond and number it so that the double bond gets the lowest locant.
Explanation:The given compound is
CH3​−CH=C(CH3​)−CH(Br)−CH3​.
The longest chain containing the double bond has 5 carbon atoms, so the parent is pentene.
Number from the end nearer to the double bond.
The double bond is between C-2 and C-3, giving pent-2-ene.
A methyl group is on C-3 and a bromo group is on C-4.
Alphabetically, bromo is written before methyl.
Hence, the IUPAC name is 4-bromo-3-methylpent-2-ene.
Numbering from the opposite end would give the double bond locant 3, which is not preferred.
Answer:Option B: 4-Bromo-3-methylpent-2-ene
