SN1 / SN2 / E1 / E2 Decision Tree for Orgo & Olympiad

Start with the substrate

• Methyl / primary → SN2 (unless bulky base → E2).
• Secondary → competition; check base strength and heat.
• Tertiary → SN1/E1 (polar protic) or E2 (strong base).

Base / nucleophile strength

Strong bulky bases (t-BuOK) favor E2. Good nucleophiles that are weaker bases favor SN2. Weak nucleophiles in polar protic solvent open the door to SN1/E1.

Heat and leaving groups

Heat tilts toward elimination. Excellent leaving groups (I⁻, OTs⁻) accelerate both substitution and elimination — the rest of the conditions decide which wins.

Train with the free tool

Open the SN1/SN2/E1/E2 Predictor and change conditions live. Free trial is 15 days; student full access is $15/year.