Question

The reactions which cannot be applied to prepare an alkene by elimination, are

Choose the correct answer from the options given below:

• A. B & E Only
• B. B, C & D Only
• C. A, C & D Only
• D. B & D Only

Hint:

In elimination reactions, strong bases such as NaOEt or NaOMe can induce E2 eliminations, while aqueous KOH typically favors SN2 reactions. Additionally, oxidation reactions like in Reaction D do not lead to alkenes via elimination.

Answer 1

The Correct Option is D

This question asks to identify reactions that are unsuitable for preparing an alkene via elimination. Elimination reactions involve the removal of a small molecule from adjacent carbon atoms, resulting in the formation of a double bond.

1. Option A depicts dehydrohalogenation using NaOEt, a strong base, which eliminates HBr from the substrate to form an alkene. This is a valid elimination reaction.
2. Option B involves KOH(aq), a reagent that typically promotes nucleophilic substitution rather than elimination. Therefore, it is generally ineffective for preparing alkenes in this scenario.
3. Option C uses NaOMe, another strong base, which is commonly employed to promote elimination (dehydrohalogenation) and form alkenes, thus representing a valid elimination process.
4. Option D shows potassium hydroxide with phenol, which favors reaction mechanisms such as nucleophilic aromatic substitution or condensation reactions, and not typically alkene formation.
5. Option E illustrates the dehydration of an alcohol at 573 K, a standard elimination reaction that forms an alkene by removing water (H₂O).

Based on this analysis, Options B and D are not typically used for alkene preparation via elimination reactions. Consequently, the correct answer is B & D Only.