JEE Chemistry 2025 Question with Solution

Given: Five reactions A to E are shown, and we must identify which reactions cannot be applied to prepare an alkene by elimination.

Find: The correct option containing the reactions that do not give alkene formation by elimination.

Elimination reactions generally remove a small molecule such as $\text{HX}$ or $\text{H}_2\text{O}$ from adjacent atoms to form a double bond.

From the provided solution:

1. Reaction A uses NaOEt, a strong base, so dehydrohalogenation can occur. It is a valid elimination reaction.
2. Reaction B uses KOH(aq), which generally favors nucleophilic substitution rather than elimination in this context. So it is not suitable here for preparing an alkene by elimination.
3. Reaction C uses NaOMe, a strong base that promotes elimination. So it is a valid elimination reaction.
4. Reaction D is described as an oxidation-type process and not an elimination route to an alkene. So it is not suitable.
5. Reaction E at $573 \, \text{K}$ is a dehydration/elimination process and is valid for alkene preparation.

Therefore, the reactions that cannot be applied are B and D.

The correct option is D.

Given: Reactions A to E.

Find: Which reactions cannot be used to prepare an alkene by elimination.

Step 1: Reaction A NaOEt is a strong base and commonly causes dehydrohalogenation. So A is a valid elimination reaction.

Step 2: Reaction B KOH(aq) usually favors substitution over elimination under these conditions. So B is not normally used here to prepare an alkene by elimination.

Step 3: Reaction C NaOMe is a strong base and can abstract a $\beta$-hydrogen to give elimination. So C is valid.

Step 4: Reaction D This reaction proceeds through oxidation-related chemistry rather than elimination to an alkene. So D is not valid for alkene preparation by elimination.

Step 5: Reaction E Heating the alcohol at $573 \, \text{K}$ gives dehydration, which is a standard elimination route to an alkene. So E is valid.

Hence, the invalid reactions are B and D.

Therefore, the correct option is D.

The answer key and the solution conclusion agree.