Organic Chemistry Lecture Notes

Overview of Reactions

Initial Scenario

• Start with two carbons and an R group → two reactions lead to different products
• Product 1: Methyl Ketone
• Product 2: Aldehyde
• Both start from the same reagents

Importance of Reagent Choice

• Determines regiochemistry
• Defines different product outcomes

Reaction 1: Formation of Methyl Ketone

• Reagents: Acid Catalyzed Hydration
  • Sulfuric acid (H₂SO₄)
  • Water (H₂O)
  • Mercury sulfate (HgSO₄) catalyst
• Mechanism: Gives enol → tautomerizes to methyl ketone

Reaction 2: Formation of Aldehyde

• Reagents: Hydroboration-Oxidation
  • Borane (BH₃/THF)
  • Hydrogen Peroxide (H₂O₂) and Sodium Hydroxide (NaOH)
• Steps:
  • Step 1: Hydroboration with BH₃
  • Step 2: Oxidation with H₂O₂/NaOH
  • Results in aldehyde

Key Points to Remember

• Methyl Ketone Formation: Acid-catalyzed hydration of terminal alkyne
• Aldehyde Formation: Hydroboration-oxidation of terminal alkyne

Reaction 3: Halogenation of Alkynes

• Halogenation can occur twice because alkynes have two π bonds
• Reagents:
  • Chlorine (Cl₂) or Bromine (Br₂) (Fluorine is too reactive, Iodine is too slow)
• Mechanisms:
  • Add halogen once with one equivalent → gives mixture
    • Major and minor products based on steric argument
  • Add halogen twice with excess halogen → two additions

Reaction 4: Ozonolysis of Alkynes

• Reagents: Ozone (O₃) followed by water (H₂O)
• Products: Carboxylic acids (internal alkyne) or carboxylic acid and CO₂ (terminal alkyne)
• Mechanism: Breaks triple bond to form products

Reaction 5: Alkylation of Terminal Alkynes

• Reagents:
  • Step 1: Sodium Amide (NaNH₂) to form alkynide ion
  • Step 2: Primary alkyl halide (e.g., R-X where X = Cl, Br, I)
• Products: New carbon-carbon bond (important for organic synthesis)
• Mechanism: SN2 reaction
  • Precaution: Primary alkyl halides only (Secondary will lead to elimination)
• Use of Acetylene:
  • Can alkylate one or both hydrogens
  • Double equivalent leads to internal alkyne formation