Ketone: Meaning (information, definition, explanation, facts)

A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a compound that contains this functional group. A ketone can be generally represented by the formula:

R₁(CO)R₂.

Among the other oxygen-containing compounds, the fact that ketones feature a carbonyl carbon bonded to two carbon atoms distinguishes them from carboxylic acids, aldehydes, esters, and amides. The double-bonded nature of the carbonyl group distinguishes ketones from alcohols and ethers. The smallest ketone is acetone:

Structure

The ketone functional group is a carbonyl group bonded to two carbon atoms.

Carbonyl group

A carbonyl group consists of a carbon atom doubly bonded to an oxygen atom.

A carbon atom adjacent to a carbonyl group is called an α carbon. Hydrogens attached to this carbon are called α hydrogens.

The carbonyl group is also found in:

• Aldehydes.
• Carboxylic acids.

IUPAC

Ketones are named using IUPAC nomenclature by changing the suffix -e of the parent alkane to -one.

A carbonyl group is polar. This makes ketones polar compounds. The carbonyl groups interact with water by hydrogen bonding.

Spectroscopic properties

Spectroscopy is an important means for identifying ketones.

Synthesis

Ketones can be created by oxidation of secondary alcohols. The process requires a strong oxidising agent such as potassium dichromate or other reageant containing Cr(VI). The alcohol is oxidised by heating under reflux in acidified solution. For example 2-propanol is oxidised to propanone (acetone):

H₃C-CH(OH)-CH₃ → H₃C-CO-CH₃

Two atoms of hydrogen are removed, leaving a single oxygen atom double bonded to a carbon atom.

Reactions

Nucleophilic addition

ketone + nucleophile → tetrahedral carbonyl addition compound

1. ketone + anion of terminal alkyne → tetrahedral carbonyl addition compound (alkoxide)
   • alkoxide + aqueous acid → hydroxyalkyne
2. ketone + ammonia or primary amine ↔ tetrahedral carbonyl addition compound
   • tetrahedral carbonyl addition compound + acid catalyst → imine + water
3. ketone + secondary amine ↔ tetrahedral carbonyl addition compound
   • tetrahedral carbonyl addition compound + acid catalyst → enamine + water
4. ketone + Grignard reagent → magnesium alkoxide
   • magnesium alkoxide + aqueous acid → tertiary alcohol
5. ketone + organolithium reagent → lithium alkoxide
   • lithium alkoxide + aqueous acid → tertiary alcohol
6. ketone + alcohol + acid or base ↔ hemiacetal + water
   • hemiacetal + alcohol + acid catalyst ↔ acetal + water
   • This is a carbonyl-protecting reaction.

Electrophilic addition

1. ketone + electrophile → resonance stabilized cation

Wittig reaction

1. • ketone + phosphonium ylide → oxphosphetane
     • oxphosphetane → phosphine oxide + alkene

Other

1. ketone + water ↔ geminal diol
2. ketone + thiol + acid catalyst ↔ thioacetal + water
3. ketone + hydrazine or derivative of hydrazine → hydrazone
4. ketone + metal hydride → metal alkoxide salt
   • metal alkoxide salt + water → alcohol

Keto-enol tautomerism

1. ketone + acid catalyst ↔ enol
   • enol + halogen → α-haloketone

Reactions at an α-carbon

1. ketone + aqueous deuterium + D⁺ or OD^- catalyst → ketone-d + HOD

Ketones (or ketone bodies) are a breakdown product of fatty acids and are elevated (in blood or urine samples) in starvation and some acute cases of diabetes mellitus (type I). These ketones are acetone, acetoacetate and beta-hydroxybutyrate.

Ketones are often used in perfumes and paints to stabilize the other ingredients so that they don't degrade over time as quickly.

• Acetophenone
• Butanone (methyl ethyl ketone)
• Acetone (propanone)