Aldehydes and Ketones

Overview

Description

Aldehydes and ketones are carbonyls. Carbonyls (C=O\rm{C{=}O}) have a carbon atom that double bonds to an oxygen, which is a highly electronegative atom. Aldehydes (RC(=O)H {\rm{RC({=}O)H}}) have an R group and a hydrogen attached to the carbonyl carbon. Ketones (RC(=O)R{\rm{RC({=}O)R'}}) have two R groups attached to the carbonyl carbon. Aldehydes are indicated by changing the suffix from -ane to -anal. Ketones are indicated by changing the suffix from -ane to -anone. Aldehydes are generally more reactive than ketones because of steric and electronic factors.

Hydrogen atoms attached to the carbonyl carbon of an aldehyde appear near 10 ppm in 1H NMR spectra. The hydrogen atoms attached to carbon atoms adjacent to the carbonyl groups of aldehydes or ketones appear near 2–3 ppm in 1H NMR spectra. Aldehydes are prepared with the oxidation of primary alcohols, ozonolysis of monosubstituted alkenes, and hydroboration-oxidation of terminal alkynes. Ketones are prepared by oxidation of secondary alcohols, ozonolysis of disubstituted alkenes, oxymercuration-demercuration hydration of terminal alkynes, and Friedel-Crafts acylation of benzene and aromatic compounds.

At A Glance

  • Aldehydes and ketones are carbonyls. In IUPAC nomenclature, aldehydes are indicated by changing the suffix from -ane to -anal. Ketones are indicated by changing the suffix from -ane to -anone. In general, aldehydes are more reactive than ketones.
  • Aldehydes are prepared by oxidation of primary alcohols with PCC, Swern oxidation, or Dess-Martin periodinane. Aldehydes are also prepared via the ozonolysis of alkenes that have one or more vinylic hydrogens (hydrogens attached to the double bond). In addition, aldehydes are prepared via hydroboration-oxidation hydration of terminal alkynes.
  • Ketones are prepared by oxidation of secondary alcohols with all oxidizing reagents. Ketones are also prepared via the ozonolysis of alkenes that are disubstituted. In addition, ketones are prepared via oxymercuration-demercuration hydration of terminal alkynes or by Friedel-Crafts acylation of benzene.