Elimination Reactions (E1 & E2)

⚗️ Elimination Reactions

Part 1 of 7 — Introduction to Elimination

1. Elimination

removal of H and leaving group → alkene

2. Base removes a proton; leaving group departs

Base removes a proton; leaving group departs

3. Two mechanisms

E1 and E2

4. Competes with substitution (SN1/SN2)

Competes with substitution (SN1/SN2)

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Key Concepts Summary

• Elimination: removal of H and leaving group → alkene
• Base removes a proton; leaving group departs
• Two mechanisms: E1 and E2
• Competes with substitution (SN1/SN2)

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E2 Mechanism

Part 2 of 7 — E2 Mechanism

1. E2

one-step, concerted (bimolecular)

2. Rate = k[substrate][base]

Rate = k[substrate][base]

3. Requires anti-periplanar geometry (H and LG 180° apart)

Requires anti-periplanar geometry (H and LG 180° apart)

4. Strong, bulky bases favor E2 (t-BuOK, DBU)

Strong, bulky bases favor E2 (t-BuOK, DBU)

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Key Concepts Summary

• E2: one-step, concerted (bimolecular)
• Rate = k[substrate][base]
• Requires anti-periplanar geometry (H and LG 180° apart)
• Strong, bulky bases favor E2 (t-BuOK, DBU)

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E1 Mechanism

Part 3 of 7 — E1 Mechanism

1. E1

two-step via carbocation (unimolecular)

2. Step 1

leaving group departs → carbocation

3. Step 2

base removes adjacent proton

4. Rate = k[substrate]; favored by weak bases, polar protic solvents

Rate = k[substrate]; favored by weak bases, polar protic solvents

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Key Concepts Summary

• E1: two-step via carbocation (unimolecular)
• Step 1: leaving group departs → carbocation
• Step 2: base removes adjacent proton
• Rate = k[substrate]; favored by weak bases, polar protic solvents

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Zaitsev vs Hofmann

Part 4 of 7 — Zaitsev vs Hofmann

1. Zaitsev's rule

more substituted alkene is major product (more stable)

2. Hofmann product

less substituted alkene (with bulky base)

3. E2 with small base → Zaitsev product

E2 with small base → Zaitsev product

4. E2 with bulky base (t-BuOK) → Hofmann product

E2 with bulky base (t-BuOK) → Hofmann product

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Key Concepts Summary

• Zaitsev's rule: more substituted alkene is major product (more stable)
• Hofmann product: less substituted alkene (with bulky base)
• E2 with small base → Zaitsev product
• E2 with bulky base (t-BuOK) → Hofmann product

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Substitution vs Elimination

Part 5 of 7 — Substitution vs Elimination

1. Strong base + primary substrate → SN2 or E2

Strong base + primary substrate → SN2 or E2

2. Strong bulky base → E2 favored over SN2

Strong bulky base → E2 favored over SN2

3. Weak base + tertiary substrate → SN1 or E1

Weak base + tertiary substrate → SN1 or E1

4. Temperature increase favors elimination over substitution

Temperature increase favors elimination over substitution

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Key Concepts Summary

• Strong base + primary substrate → SN2 or E2
• Strong bulky base → E2 favored over SN2
• Weak base + tertiary substrate → SN1 or E1
• Temperature increase favors elimination over substitution

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Problem-Solving Workshop

Part 6 of 7 — Problem-Solving Workshop

1. Predicting elimination products

Predicting elimination products

2. Distinguishing E1 from E2

Distinguishing E1 from E2

3. Choosing between substitution and elimination

Choosing between substitution and elimination

4. Drawing mechanisms and predicting stereochemistry

Drawing mechanisms and predicting stereochemistry

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Key Concepts Summary

• Predicting elimination products
• Distinguishing E1 from E2
• Choosing between substitution and elimination
• Drawing mechanisms and predicting stereochemistry

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Synthesis & Review

Part 7 of 7 — Synthesis & Review

1. Elimination competes with substitution

Elimination competes with substitution

2. Reaction conditions determine which pathway dominates

Reaction conditions determine which pathway dominates

3. E2 requires specific geometry

E2 requires specific geometry

4. Review

SN1/SN2/E1/E2 decision flowchart

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Key Concepts Summary

• Elimination competes with substitution
• Reaction conditions determine which pathway dominates
• E2 requires specific geometry
• Review: SN1/SN2/E1/E2 decision flowchart

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