Lecture Notes on Rearrangement Reactions

Introduction

• Completed oxidation reactions
• Starting rearrangement reactions
• This video focuses on introduction and basics of rearrangement reactions

What are Rearrangement Reactions?

• Definition: Movement of a group within the same molecule to form a rearranged product
• Example: Rearranging items in a room
  • Not adding new items, just repositioning existing ones
  • Similar concept in chemistry

Characteristics of Rearrangement Reactions

• Specific mechanism is followed, not random
• The resulting product must be stable
• Driving force of rearrangement is the formation of a stable intermediate or product

Terminology

1. Migrating Group (W): Group that moves within the molecule
2. Migration Origin (B): Initial position of the migrating group
3. Migration Terminus (C): Final position of the migrating group

Types of Rearrangement Reactions

• One-Two Shifts (1,2-shifts): Most common type, involves migration from one atom to an adjacent atom
• Stability of the intermediate state (transition state) determines the ease of the reaction

Examples

• Pinacol Rearrangement (1,2-shift): Shifts a group from one carbon to an adjacent carbon
• Transition State: Presence of electrons in bonding/antibonding molecular orbitals crucial

Energy Profile Diagram

• Defines stability of intermediates
• Electrophilic Rearrangement: Highest energy transition state
• Nucleophilic Rearrangement: Lowest energy transition state, most common due to stability

Mechanism of Migration

• Nucleophilic Migration: Carries both bonding electrons, stable intermediate
• Electrophilic Migration: Without bonding electrons, less stable
• Radical Migration: Carries one electron, intermediate stability

Rearrangement Intermediates

1. Carbocation Intermediates: Crucial in many rearrangements
   • Examples: Pinacol Rearrangement, Wagner-Meerwein Rearrangement
2. Nitrenium Ion Intermediates: Found in Hoffmann Rearrangement, Beckmann Rearrangement
3. Radical Intermediates: Less common, but significant in specific reactions
4. Carbonyl Intermediates: Unique cases like Baeyer-Villiger Oxidation

Outline of Rearrangement Reactions to be Studied

1. **Carbocation Intermediates: (Electro-positive carbon atoms) **
   • Pinacol Rearrangement
   • Wagner-Meerwein Rearrangement
2. Nitrenium Ion Intermediates: (Electro-positive nitrogen atoms)
   • Hoffmann Rearrangement
   • Beckmann Rearrangement
3. Radical Intermediates: (Electro-deficient radicals)
   • Reactions not specified in the syllabus
4. Carbonyl Intermediates: (Electro-rich carbon atoms)
   • Baeyer-Villiger Oxidation
   • No specific intermediate, stable product formation

Final Remarks

• Importance of understanding the syllabus and the specific intermediates involved
• Reviewing mechanisms and practicing examples
• Emphasis on clarity and familiarity with rearrangement reactions for exams