E1 vs E2: The Exam Decision Tree for Elimination

Use a clear decision tree to choose E1 vs E2 based on base strength, substrate, solvent, and temperature. Includes Zaitsev vs Hofmann, rearrangements, and stereochemical rules.

• Fastest decision: Base strength + substrate class.
• E2 signature: Strong base (often negatively charged) + 1°/2°/3° substrate with β‑H
• E1 signature: Weak base + 3° (or resonance-stabilized) substrate + polar protic + heat
• Rearrangements: Only E1 (carbocation) can rearrange
• Stereochemistry: E2 can be stereospecific in rings; E1 usually gives mixtures
• Exam type: Choose the mechanism
• Exam type: Predict the major product
• Exam type: Regiochemistry