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JEE Chemistry Focus Reading Time: 14 min 2 Key Rules

Saytzeff vs Hofmann: The Battle for the Major Product in Elimination Reactions

Master the art of predicting major alkene products based on base strength, substrate structure, and reaction conditions.

2
Key Rules
100%
JEE Relevance
6+
Examples
18min
Practice Time

The Elimination Reaction Dilemma

In β-elimination reactions, multiple alkenes can form, but one usually dominates. Understanding Saytzeff and Hofmann rules is crucial for:

  • Predicting major products in JEE multiple-choice questions
  • Understanding reaction mechanisms and stability factors
  • Solving complex synthesis problems in JEE Advanced
  • Avoiding common traps in product prediction
Saytzeff Rule Thermodynamic Control

Saytzeff (Zaitsev) Rule: The More Substituted Alkene Wins

"In elimination reactions, the more highly substituted alkene (more alkyl groups on C=C) is the major product"

🔬 Governing Factors:

Stability Order: Tetra-substituted > Tri-substituted > Di-substituted > Mono-substituted

Reason: Hyperconjugation and alkyl group electron donation stabilize the alkene

Conditions: Strong bases (OH⁻, OR⁻), high temperature, unimolecular elimination

🎯 Classic Example:

Reaction: 2-bromobutane + ethoxide → ?

CH₃-CH₂-CH(Br)-CH₃ + EtO⁻ → CH₃-CH=CH-CH₃ (80%) + CH₃-CH₂-CH=CH₂ (20%)

Explanation: But-2-ene (disubstituted) is more stable than but-1-ene (monosubstituted) due to hyperconjugation

Hofmann Rule Steric Control

Hofmann Rule: The Less Substituted Alkene Wins

"With bulky bases or quaternary ammonium salts, the less substituted alkene becomes major"

🔬 Governing Factors:

Base Types: Bulky bases (t-butoxide), poor leaving groups (NR₃⁺)

Reason: Steric hindrance prevents access to more substituted β-hydrogens

Conditions: Bulky bases, quaternary ammonium hydroxides, bimolecular elimination

🎯 Classic Example:

Reaction: 2-bromobutane + t-butoxide → ?

CH₃-CH₂-CH(Br)-CH₃ + t-BuO⁻ → CH₃-CH₂-CH=CH₂ (70%) + CH₃-CH=CH-CH₃ (30%)

Explanation: Bulky t-butoxide cannot easily access sterically hindered β-hydrogens, favoring less substituted product

⚖️ Saytzeff vs Hofmann: Quick Comparison

Factor Saytzeff Product Hofmann Product
Substitution More substituted Less substituted
Base Used Small bases (OH⁻, CH₃O⁻) Bulky bases (t-BuO⁻)
Leaving Group Good (Br⁻, Cl⁻) Poor (NR₃⁺)
Control Type Thermodynamic Steric/Kinetic
Stability More stable Less stable

🎯 Quick Decision Guide

Saytzeff Product Dominates When:

  • Small base (OH⁻, RO⁻)
  • Good leaving group (I⁻, Br⁻, Cl⁻)
  • No steric hindrance around β-hydrogens
  • High temperature conditions
  • E1 mechanism favored

Hofmann Product Dominates When:

  • Bulky base (t-BuO⁻)
  • Poor leaving group (NR₃⁺, F⁻)
  • Steric hindrance around β-hydrogens
  • Quaternary ammonium substrates
  • E2 mechanism with hindered access

Advanced Applications Available

Includes E1 vs E2 mechanisms, stereochemistry, and JEE Advanced level problems

🧪 Quick Self-Test

Predict the major product in these elimination reactions:

1. CH₃-CH₂-CH(Br)-CH₃ + KOH/ethanol → ?

2. (CH₃)₃C-N⁺(CH₃)₃ OH⁻ + heat → ?

3. CH₃-CH₂-C(Br)(CH₃)-CH₃ + t-BuOK → ?

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