JEE Chemistry 2026 Question with Solution

Given: List I contains pairs of organic compounds and List II contains types of isomerism.

Find: The correct matching between the compound pairs and the isomer types.

Step 1: Understanding the concept Isomers are molecules with the same molecular formula but different arrangements of atoms. Structural isomers include chain, position, and functional isomers. Stereoisomers include geometric and optical isomers.

Step 2: Match each pair

For A. 2-Methylpropene and but-1-ene:

Both have the same molecular formula. 2-Methylpropene has a branched carbon skeleton, whereas but-1-ene has a straight chain. Therefore, these are chain isomers (III).

For B. cis-but-2-ene and trans-but-2-ene: These differ in spatial arrangement around the double bond. Therefore, these are geometric isomers, which are a type of stereoisomers (I).

For C. 2-Butanol and diethyl ether:

One is an alcohol and the other is an ether. Therefore, these are functional group isomers (IV).

For D. But-1-ene and but-2-ene: These differ only in the position of the double bond, at $\mathrm{C1}$ versus $\mathrm{C2}$. Therefore, these are position isomers (II).

Conclusion: The correct matching is A-III, B-I, C-IV, D-II. Therefore, the correct option is D.

Given: Four compound pairs are to be matched with four isomer categories.

Find: Which option gives the correct one-to-one correspondence.

1. Chain isomerism occurs when compounds have the same molecular formula but different carbon skeletons.
2. Stereoisomerism occurs when connectivity is same but spatial arrangement differs.
3. Functional group isomerism occurs when compounds have the same molecular formula but different functional groups.
4. Position isomerism occurs when the same functional group or multiple bond is present at different positions.

Applying these definitions:

• A matches III.
• B matches I.
• C matches IV.
• D matches II.

Hence the final matching is A-III, B-I, C-IV, D-II, so the correct option is D.