Analyzing Organic Reactions: SN1 Reactions and Redox Reactions

Introduction

• Presenter: Iman
• Topic: SN1 reactions and oxidation-reduction (redox) reactions
• Previous Lecture: SN2 reactions

SN1 Reactions

• Mechanism: Two-step process
  1. Step 1: Leaving group leaves, forming a carbocation (positively charged carbon ion)
     • Can lead to carbocation rearrangement (methyl or hydride shift for stability)
  2. Step 2: Nucleophile attacks the planar carbocation from either side, resulting in a racemic mixture of products
• Rate-Determining Step: Only depends on the concentration of the substrate
  • Reaction is unimolecular (hence SN1)
• Stability: Prefers more substituted carbons (alkyl groups donate electron density and stabilize positive charge)

Comparison: SN1 vs. SN2

• SN1: Two-Step Process
  • Formation of carbocation intermediate
  • Nucleophilic attack from either side
  • Prefers more substituted carbons
• SN2: One-Step Process
  • Nucleophile attacks as the leaving group leaves
  • Requires backside attack, leading to inversion of stereochemistry
  • Prefers less substituted carbons (less steric hindrance)
  • Rate depends on both substrate and nucleophile

Redox Reactions

• Definition: Transfer of electrons between species
  • Oxidation: Loss of electrons (OIL - Oxidation Is Loss)
  • Reduction: Gain of electrons (RIG - Reduction Is Gain)
• Law of Conservation of Charge: Electrical charge can neither be created nor destroyed
• Concepts:
  • Oxidation increases oxidation state
  • Reduction decreases oxidation state
  • Oxidation: Increase in bonds to oxygen/heteroatoms
  • Reduction: Increase in bonds to hydrogen

Oxidizing and Reducing Agents

• Oxidizing Agent: Substance that gains electrons (is reduced)
• Reducing Agent: Substance that loses electrons (is oxidized)

Oxidation Reactions in Organic Chemistry

• Examples:
  • Primary alcohol to aldehyde (PCC)
  • Primary alcohol to carboxylic acid (strong oxidizing agents: CrO3, Na/K dichromate, KMnO4)
  • Secondary alcohol to ketone (PCC)
  • Aldehyde to carboxylic acid (strong oxidizing agents)
  • Alkene to carboxylic acid (KMnO4)
• Themes:
  • Oxidation increases bonds to oxygen
  • Oxidizing agents contain metals bonded to many oxygen atoms

Reduction Reactions in Organic Chemistry

• Examples:
  • Aldehydes/ketones to primary/secondary alcohols (catalyst needed)
  • Amides to amines (LiAlH4)
  • Carboxylic acids to primary alcohols (LiAlH4)
  • Esters to alcohols (LiAlH4)
• Themes:
  • Reduction increases bonds to hydrogen
  • Reducing agents contain metals bonded to many hydrides

Conclusion

• Next Topics:
  1. Chemoselectivity
  2. Step-by-step guide to problem-solving organic chemistry reactions