Advanced Topic 790 of 1102 Organic Chemistry
E2 Elimination
A one-step bimolecular elimination requiring a strong base and anti-periplanar geometry.
In-depth explanation of E2 Elimination
E2 elimination is a one-step bimolecular elimination in which a strong base removes a proton from a carbon adjacent to the leaving group while the leaving group departs at the same time. The rate law is rate equal to k times the haloalkane concentration times the base concentration. For a concerted reaction the best geometry is anti-periplanar, with the hydrogen and leaving group on opposite sides of the bond and in the same plane. E2 is favoured by strong, often bulky bases and by heat, and it usually gives the Zaitsev product unless a very bulky base forces the Hofmann product.
Going deeper: E2 Elimination
Key ideas: Concerted, bimolecular: the base removes a beta hydrogen while the leaving group departs, with H and X anti-periplanar (180 degrees dihedral). Rate equals k times halide times base. Requires a strong base (ethoxide, tert-butoxide, NaNH2) and works for primary, secondary and tertiary halides. In cyclohexanes the leaving group and beta hydrogen must both be axial. Bulky bases give the Hofmann (less substituted) alkene.
Common mistakes and connections: Students ignore the anti-periplanar requirement, getting the wrong alkene stereochemistry. Another error is believing alcoholic KOH gives substitution; alcoholic KOH favours elimination, aqueous KOH favours substitution. Links to the Zaitsev rule, SN2 competition and stereospecific outcomes in rings.
Visualization of E2 Elimination
A strong base removes a proton while the leaving group departs in one anti-periplanar step, forming the C=C bond. The interactive lesson shows this as a live animation or chart.
Worked example and use case
2-Bromopropane treated with ethanolic potassium hydroxide gives propene by E2 elimination.
Frequently asked questions about E2 Elimination
What is E2 Elimination?
A one-step bimolecular elimination requiring a strong base and anti-periplanar geometry.
Is E2 Elimination a beginner, intermediate or advanced topic?
E2 Elimination is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before E2 Elimination?
Study these earlier topics in Organic Chemistry first: SN1 Reaction, SN2 Reaction, E1 Elimination.
What comes after E2 Elimination?
The next topics in Organic Chemistry are Zaitsev's Rule and Alcohols.
Can I practise E2 Elimination with quizzes?
Yes. The interactive lesson includes a self-check question on E2 Elimination, and the Organic Chemistry quiz draws on every topic in this area.
Where E2 Elimination fits in Organic Chemistry
E2 Elimination is topic 62 of 148 in Organic Chemistry.