Crash Course Organic Chemistry: Aldehydes and Ketones

Introduction

• Presented by Deboki Chakravarti
• Aldehydes and ketones are known for their strong, often sweet smells.
• Examples:
  • Ketone: Acetone (nail polish remover)
  • Aldehydes: Vanillin and cinnamaldehyde
• Importance in biochemistry and drugs:
  • Ketone groups in sex hormones (e.g., progesterone, testosterone)
  • Medications like cortisone and dexamethasone

Carbonyl Groups

• Composed of a carbon double-bonded to an oxygen.
• Carbonyl Carbon:
  • Aldehyde: At the end of a chain (attached to a carbon group and a hydrogen)
  • Ketone: Attached to two carbon groups

Nomenclature

• Aldehydes: Add “al” to the carbon chain name, e.g., methanal, ethanal.
  • Common names often end in "aldehyde," e.g., acetaldehyde, formaldehyde.
• Ketones: End in "one," e.g., acetone, acetophenone.

Synthesis of Aldehydes and Ketones

• Aldehydes:
  • Oxidation of primary alcohols (pyridinium chlorochromate as a weaker oxidizing agent).
• Ketones:
  • Oxidation of secondary alcohols with strong oxidizing agents (e.g., chromium VI).

Techniques: Reflux

• Involves heating a chemical mixture while cooling evaporated solvent to condense back into the liquid.

Environmental Concerns

• Chromium VI is toxic; alternatives like ozone (ozonolysis) are more environmentally friendly.

Hydroboration and Oxymercuration

• Hydroboration: Anti-Markovnikov addition to form less substituted enol, using reagents like borane-THF.
• Oxymercuration: Markovnikov addition to form more substituted alcohol.

Nucleophilic Addition Reactions

• Carbonyl Carbon is a target for nucleophilic attack.
• Use of cyanide salts and acetylide anion as nucleophiles.

Reduction Reactions

• Sodium borohydride and lithium aluminum hydride as hydride reagents.
• Mechanism results in alcohol formation (primary or secondary depending on starting material).

The Wittig Reaction

• Reacts aldehydes/ketones with phosphonium ylide, forming alkenes and triphenylphosphine oxide.
• Forms Z-alkene as a major product.

Summary

• Aldehydes and ketones:
  • Contain carbonyl groups, susceptible to nucleophilic attack.
  • Formed by oxidizing alcohols.
  • Reduced to form alcohols.
  • Extend carbon chains via ylides.

Conclusion

• Next topic: Organometallic chemistry.
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