Answer
Elimination Reaction Mechanisms and Products
Reaction (i): Double Elimination Using NaNH₂
Reagents: Geminal dichloride compound, Sodium amide (NaNH₂, 2 equivalents)
Mechanism: Strong base-induced double dehydrohalogenation (E2 type)
- Step 1: NaNH₂ eliminates HCl forming vinyl chloride
- Step 2: A second elimination yields an internal alkyne
The product is a linear internal alkyne, formed by two successive E2 eliminations using NaNH₂, a strong base.
Reaction (ii): Elimination Using EtOH and Weak Base
Reagents: Tertiary alkyl bromide, Ethanol (EtOH)
Mechanism: Unimolecular Elimination (E1 type)
- Step 1: Loss of Br⁻ forms a tertiary carbocation
- Step 2: Proton abstraction by ethanol yields a substituted alkene
According to Zaitsev’s Rule, the most stable product is the tri-substituted alkene, due to increased alkyl substitution around the double bond.
Summary of Reaction Products
| Reaction | Mechanism | Product Type | Key Notes |
|---|---|---|---|
| (i) | E2 (twice) | Internal Alkyne | NaNH₂ eliminates two HCl molecules |
| (ii) | E1 | Tri-substituted Alkene | Follows Zaitsev’s Rule |