JEE Chemistry 2025 Question with Solution

Given: The compound has a longest chain containing the double bond and the shown substituents.

Find: The correct IUPAC name.

The solution identifies the longest continuous chain containing the double bond as a 4-carbon chain, so the parent hydrocarbon is butene.

The chain is numbered so that the double bond gets the lowest possible locant. The double bond lies between carbon $2$ and carbon $3$, so the parent name is but-2-ene.

From the solution text, the substituents are:

• a methyl group at carbon $2$
• a bromo group at carbon $1$

Combining the substituents with the parent name gives 1-Bromo-2-methylbut-2-ene.

Therefore, the correct option is C.

Given: An unsaturated organic compound is to be named using IUPAC rules.

Find: The correct option corresponding to its IUPAC name.

1. Identify the longest carbon chain containing the double bond. The solution states that this chain has 4 carbon atoms, so the root word is but-.
2. Identify the double bond position. It is between carbon $2$ and carbon $3$, giving but-2-ene.
3. Identify the substituents. The solution states that there is a methyl substituent at carbon $2$ and a bromo substituent at carbon $1$.
4. Write substituents with locants and then the parent name: 1-Bromo-2-methylbut-2-ene.

Thus, the correct IUPAC name is 1-Bromo-2-methylbut-2-ene, so the correct option is C.