Lecture Notes: Naming Aldehydes and Ketones

Aldehydes

• Structure: Carbonyl (C=O) with an alkyl group on one side and a hydrogen on the other.
• Naming Simple Aldehydes:
  • Drop the "e" from the alkane name and add "-al."
  • Example: Four-carbon aldehyde = "Butanal."
• Numbering:
  • Carbonyl carbon gets the lowest number.
  • Priority over double bonds, alkyl groups, halogens.
  • Example: Five-carbon aldehyde with bromine = "four-bromopentanal."
• Examples:
  • Three-carbon aldehyde with a double bond = "Two-propenal."
  • If there's a phenyl group at carbon three: "E-three-phenyl two-propenal" or "E-three-phenyl prop-two-en-al."
  • Common name: Cinnamaldehyde (gives cinnamon smell).

Common Aldehydes

• Benzaldehyde:
  • Incorporated into IUPAC nomenclature.
  • Smells like almonds.
  • Used in compounds like vanillin.

Additional Aldehyde Examples

• Cyclohexane carbaldehyde:
  • For molecules without a benzene ring.
• Pentanedial (dial):
  • Two aldehydes in the same molecule, e.g., "one-five-pentanedial."

Ketones

• Structure: Carbonyl (C=O) bonded to two alkyl groups (same or different).
• Naming Ketones:
  • Drop the "e" and add "-one."
  • Example: Four-carbon ketone = "Butanone."

Ketone Naming Methods

• Old vs New Methods:
  • Old: Name by alkyl groups (e.g., "methylethylketone").
  • Examples: "Three-hexanone" for longer ketones.
  • New: "Hexan-three-one."
• Double Bonds:
  • Example: "E-four-hexene-two-one."
  • Specify stereochemistry (trans or E).

Cyclic Ketones

• Example: Cyclohexanone:
  • With a methyl group = "Three-methylcyclohexanone."
• Multiple Ketones:
  • Two ketones: "Two-four-hexanedione" or "Hexane-two-four-dione."

Summary

• Aldehydes and ketones have specific nomenclature rules focusing on the carbonyl placement and substituents.
• Priority is given to carbonyl in numbering.
• Modern IUPAC nomenclature has updated some traditional naming methods.

This concludes the overview of naming aldehydes and ketones.