Advanced Topic 791 of 1102 Organic Chemistry
Zaitsev's Rule
The more substituted alkene is the major product of elimination.
In-depth explanation of Zaitsev's Rule
Zaitsev's rule states that in an elimination reaction the more substituted alkene, which is the more thermodynamically stable one, is the major product. The alkene is more stable because more alkyl groups on the double-bond carbons provide greater hyperconjugation and better stabilization. The rule applies to both E1 and E2 eliminations when the base is small and unhindered. Exceptions occur with bulky bases or poor leaving groups, which favour the less substituted Hofmann product because the base reaches the more accessible hydrogens.
Going deeper: Zaitsev's Rule
Key ideas: In elimination, the more substituted (more stable) alkene is the major product, e.g. 2-bromobutane with ethoxide gives mostly 2-butene (about 80 percent) over 1-butene, with trans favoured over cis. Exceptions follow Hofmann: bulky bases (tert-butoxide), poor leaving groups (fluoride) and quaternary ammonium salts give the less substituted alkene.
Common mistakes and connections: Students use Zaitsev for Hofmann elimination of quaternary ammonium hydroxides, where the opposite holds. Another mistake is forgetting trans versus cis, or that the rule reflects thermodynamic stability. Links to alkene stability, hyperconjugation, E1 and E2 mechanisms and dehydration of alcohols.
Visualization of Zaitsev's Rule
Heat of hydrogenation falls as substitution rises, so the more substituted alkene is more stable and is the major elimination product. The interactive lesson shows this as a live animation or chart.
Worked example and use case
2-Bromobutane reacts with ethanolic base to give mostly but-2-ene, which is the more substituted alkene.
Frequently asked questions about Zaitsev's Rule
What is Zaitsev's Rule?
The more substituted alkene is the major product of elimination.
Is Zaitsev's Rule a beginner, intermediate or advanced topic?
Zaitsev's Rule 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 Zaitsev's Rule?
Study these earlier topics in Organic Chemistry first: SN2 Reaction, E1 Elimination, E2 Elimination.
What comes after Zaitsev's Rule?
The next topics in Organic Chemistry are Alcohols and Properties of Alcohols.
Can I practise Zaitsev's Rule with quizzes?
Yes. The interactive lesson includes a self-check question on Zaitsev's Rule, and the Organic Chemistry quiz draws on every topic in this area.
Where Zaitsev's Rule fits in Organic Chemistry
Zaitsev's Rule is topic 63 of 148 in Organic Chemistry.