1️⃣E1 vs E22️⃣
E1 and E2 are the two main elimination mechanisms that form alkenes by removing atoms. Conditions decide which pathway wins.
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1️⃣E1
- ✓Two-step mechanism via a carbocation
- ✓Rate depends only on the substrate
- ✓Favored by tertiary substrates
- ✓Uses weak bases and heat
- ✓Can give rearranged products
2️⃣E2
- ✓One-step concerted elimination
- ✓Rate depends on substrate and base
- ✓Works on primary and secondary substrates
- ✓Requires a strong, often bulky base
- ✓Anti-periplanar geometry required
Verdict
E1 proceeds via a carbocation with a weak base, while E2 is a concerted one-step process needing a strong base. Both make alkenes but differ in rate law and stereochemistry.
Frequently asked
What base does E2 need?+
A strong base such as hydroxide or alkoxide that can pull off a proton in the concerted step.
Why can E1 give rearranged products?+
Its carbocation intermediate can shift to a more stable position before elimination.
What geometry does E2 require?+
The leaving group and the proton must be anti-periplanar, on opposite sides of the bond.
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