What is IUPAC name of Isoprene?

Isoprene is the common name for the conjugated diene with the chemical formula $C_5H_8$.

The structure of isoprene is $CH_2=C(CH_3)-CH=CH_2$.

Selecting the longest carbon chain containing both double bonds gives a four-carbon chain (butadiene).

Numbering the chain to give the lowest locants to the double bonds and substituents, the double bonds are at positions 1 and 3, and the methyl group is at position 2.

Thus, the IUPAC name is 2-methyl-1,3-butadiene.

Answer: 2-methyl- 1, 3-butadine