Answer
E2 β-Elimination Reaction Mechanism
🔹 Step 1: Understanding the Reaction Type
The reaction follows an E2 (bimolecular elimination) pathway, a single-step concerted mechanism. A base removes a β-hydrogen while the leaving group departs from the α-carbon simultaneously.
🔬 Key Features of E2 Mechanism:
- ⚡ Requires a strong base
- 📌 Occurs in one concerted step
- 📐 Needs anti-periplanar orientation between β-H and the leaving group
- 🌀 Forms an alkene directly
🧬 Mechanistic Insight
1️⃣ Base abstracts the β-hydrogen
2️⃣ Electrons from C–H bond form a π bond
3️⃣ Leaving group (Cl⁻) is eliminated simultaneously
✅ All steps occur in a single transition state
2️⃣ Electrons from C–H bond form a π bond
3️⃣ Leaving group (Cl⁻) is eliminated simultaneously
✅ All steps occur in a single transition state
📐 Newman Projection & Stereochemistry
Using the Newman projection, it becomes clear that anti-periplanar alignment of β-H and Cl is necessary. This leads to the formation of the more stable (E)-alkene.
✅ Final Answer
The product is an (E)-alkene — Option (B)
🔁 Summary Table
| Feature | Details |
|---|---|
| Reaction Type | Concerted (Single-step) |
| Base | Strong base required |
| Geometry | Anti-periplanar |
| Intermediate | None |
| Product | Alkene |
| Stereochemistry | (E)-isomer formed |
| Correct Option | Option (B) |