Lecture on Oxidation and Reduction Reactions in Organic Chemistry

Introduction

• Oxidation and Reduction (Redox) reactions are key in Organic Chemistry.
• General Chemistry mnemonics:
  • OIL RIG: Oxidation is Loss, Reduction is Gain.
  • LEO the lion says GER: Loss of Electrons is Oxidation, Gain of Electrons is Reduction.
  • These aid understanding in General Chemistry (batteries, circuits), but need adaptation for Organic Chemistry (bonds, atoms).

Basic Concepts in Organic Chemistry Redox

• Oxidation
  • Loss of hydrogen atom (proton and electron).
  • Gain of an oxygen atom (oxygen and hydrogen antagonistic).
• Reduction
  • Gain of hydrogen atom.
  • Loss of oxygen atom.
• Oxidation Numbers
  • Oxidation number increase: Oxidation (e.g., Fe2+ to Fe3+).
  • Oxidation number decrease: Reduction.

Applying Redox to Organic Compounds

• Use a combination of electron loss/gain, hydrogen/oxygen gain/loss, and oxidation numbers.

Examples

• Alkene Reactions

  • Hydration Reaction
    • With H2SO4 and H2O: pi bond is broken, forming alcohol (oxidation).
    • Oxidation state: Carbon goes from -1 to 0 (proof of oxidation).
  • Reduction Reaction
    • With H2 and palladium catalyst: Carbon gains hydrogen, saturation (reduction).
    • Oxidation state: Carbon goes from -1 to -2 (proof of reduction).

• Alkyne Reactions

  • Oxymercuration
    • With HgSO4 and H2SO4: Forms enol, tautomerizes to ketone (oxidation).
    • Oxidation state: Carbon goes from 0 to +2.
  • Reduction Options
    • Produces alkane, cis-alkene, or trans-alkene through hydrogen gain.

Alcohols in Redox Reactions

• Primary Alcohols
  • Oxidized to aldehydes (gain oxygen, lose hydrogen) and further to carboxylic acids.
  • Reverse process: Reduction.
• Secondary Alcohols
  • Oxidized to ketones, can’t be oxidized further without breaking carbon chain.
  • Reduction involves adding hydrogen.
• Tertiary Alcohols
  • Cannot be oxidized (no hydrogen to remove, can't form double bonds without violating octet).

Reagents in Redox Reactions

• Oxidation Reagents
  • Examples: KMnO4, CrO3, O3, Cr2O7²⁻.
  • Rich in oxygen, donate oxygen to the molecule.
• Reduction Reagents
  • Examples: LAH (Lithium Aluminum Hydride), NaBH4 (Sodium Borohydride).
  • Rich in hydrogen, ideal for hydrogen addition.

Conclusion and Resources

• Understanding reagents' roles in redox reactions is crucial.
• Further detailed mechanisms and examples are available in upcoming videos and on leah4sci.com/redox.