Crash Course Organic Chemistry: Aldehydes and Ketones

Introduction

• Presenter: Deboki Chakravarti
• Aldehydes and ketones are known for their strong, often sweet smells.
  • Example ketone: Acetone (nail polish remover)
  • Example aldehydes: Vanillin, Cinnamaldehyde
• Importance:
  • Present in biochemistry and drug treatments (e.g., progesterone, testosterone, cortisone, dexamethasone)
• Focus on energy-efficient and non-polluting synthesis

Carbonyl Groups

• Carbonyl: Carbon double-bonded to oxygen
  • Carbonyl Carbon: Central carbon
• Aldehydes: Carbonyl at end of chain, attached to carbon group and hydrogen
  • Naming: Standard chain name + “al” (e.g., Methanal, Ethanal)
  • Common names: Acetaldehyde, Formaldehyde
• Ketones: Carbonyl attached to two carbon groups
  • Naming: Ends in “one” (e.g., Acetone, Acetophenone)

Synthesis of Aldehydes and Ketones

Oxidation of Alcohols

• Primary Alcohols:
  • Weaker oxidizing agent: Stops at aldehyde (e.g., Pyridinium chlorochromate)
  • Strong oxidizing agents: Can form carboxylic acids (e.g., Chromic acid)
• Secondary Alcohols:
  • Can be oxidized to ketone using strong oxidizing agents

Reaction Techniques

• Reflux: Heating mixture while condensing solvent back
  • Prevents loss of solvent

Ozonolysis

• Alkene double bonds broken, forming carbonyls on each carbon
  • Example: 2-methyl-2-pentene → Acetone + Propanal

Hydroboration and Oxymercuration

• Hydroboration: Anti-Markovnikov addition (e.g., Borane-THF, 9-BBN)
• Oxymercuration: Markovnikov addition
  • Enols form and convert to more stable aldehydes/ketones

Reactions with Acid Chlorides and Esters

• Organocopper compounds: React with acid chlorides to form ketones
• Bulky reducing agents: Reduce esters to aldehydes

Nucleophilic Addition Reactions

• Carbonyl carbon is a target for nucleophilic attack due to dipole
• Cyanide and acetylide anions can be used as nucleophiles

Hydride Reagents

• Sodium Borohydride: Reduces carbonyl to alcohol
  • Mechanism: Borohydride anion attacks carbonyl → Alcohol

Wittig Reaction

• Wittig Reagent: Phosphonium ylide forms carbon-carbon bonds
  • Results in Z-alkene
  • E-alkenes can be formed with stabilized ylides

Conclusion

• Aldehydes and ketones are pivotal in organic chemistry due to their reactivity and the ability to form carbon chains.
• Next topic: Organometallic chemistry

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