MCAT Organic Chemistry: Aldehydes and Ketones Part 1

Presenter: Iman

Objectives Covered

• Description and properties of aldehydes and ketones
  • Nomenclature rules
  • Physical properties
  • Formation of aldehydes and ketones
• Nucleophilic addition reactions
• Oxidation-reduction reactions

Important Functional Group: The Carbonyl Group

• Definition: A carbonyl group is a double bond between a carbon and an oxygen
• Commonality: Found in many functional groups (e.g., aldehydes, ketones, carboxylic acids, esters, amides, anhydrides)
• Reactivity: Can act as both a nucleophile and an electrophile

Aldehydes vs. Ketones

• Aldehydes: Carbonyl carbon bonded to one alkyl group and one hydrogen
  • Always a terminal group
• Ketones: Carbonyl carbon bonded to two alkyl groups
  • Never a terminal group

Nomenclature

Aldehydes

• Suffix: Replace the 'e' at the end of the alkane name with 'al'
• Common Examples:
  • Methanal (Common: Formaldehyde)
  • Ethanal (Common: Acetaldehyde)
  • Propanal (Common: Propionaldehyde)
  • Butanal (Common: Butyraldehyde)
  • Cyclic Aldehyde: Use the suffix 'carbaldehyde' (e.g., Cyclopentanecarbaldehyde)

Ketones

• Suffix: Replace the 'e' at the end of the alkane name with 'one'
• Common Examples:
  • Propanone (Common: Acetone)
  • Butanone
• Substituents: When ketones are not the highest priority group, use the prefixes 'oxo' or 'keto'
  • E.g., 3-oxobutanoic acid
• Cyclic Ketone: Replace 'e' with 'one' (e.g., Cyclopentanone)

Physical Properties

• Dipole Moment: Stronger than alcohols due to double-bonded oxygen
• Boiling Points: Higher than parent alkanes due to increased intermolecular attractions
  • However, lower than alcohols because they do not exhibit hydrogen bonding
• Reactivity: Both aldehydes and ketones act as electrophiles in reactions
  • Aldehydes are generally more reactive towards nucleophiles than ketones (less steric hindrance and fewer electron-donating alkyl groups)

Formation

Aldehydes: From Partial Oxidation of Primary Alcohols

• Reagent: PCC (Pyridinium Chlorochromate)
  • Mild oxidant that prevents further oxidation to carboxylic acids

Ketones: From Oxidation of Secondary Alcohols

• Reagents: Sodium chromate, potassium chromate, chromium trioxide
  • No concern for over-oxidation beyond ketone stage

Next Steps

• The lecture stops here for now
• Future videos will continue the discussion, including nucleophilic addition reactions and oxidation-reduction reactions.

Conclusion

• Reach out with any questions or comments
• Good luck with your studies!