Ketone (thing)

Structure

A ketone is an organic (carbon-based) compound, that can generally be written in the form R₁-CO-R₂. A ketone is essentially an alkane of length greater than two, that contains an oxygen atom bonded to a carbon atom that is not on one of the ends of the chain.

Consider the shortest ketone, propanone (acetone). The root is propane, C₃H₈.

  H
  |
H-C-H
  |
H-C-H
  |
H-C-H
  |
  H

To form a ketone from this, remove two hydrogen atoms bonded to the middle carbon (recall, the carbon-oxygen bond must not be at the end of the chain) and replace it with an oxygen (the combining capacity of oxygen is two, so it must be double bonded with the carbon to be stable). This forms the carbonyl bond that defines a ketone.

  H
  |
H-C-H
  |
  C=O
  |
H-C-H
  |
  H

It is now a ketone, with the IUPAC name propanone, or 2-propanone.

Naming a Ketone

1. Name the longest chain of carbons as if it were an alkane. Use this as the root.
2. Determine which carbon the oxygen is double bonded to (count so that the bonded atom has the lowest number possible). Prepend this number to the root.
3. Replace the ending of the root "-e" with the ending "-one"

Properties of Ketones

The properties of ketones are similar to the properties of aldehydes. Due to the polar nature of the carbonyl bond, ketones are polar molecules, decreasing in polarity as the size of the root chain increases. Due to the polar nature of the molecule, ketones may participate in hydrogen bonding, especially with water. They will not, however, hydrogen bond with themselves, as they lack a polar bond with hydrogen. Due to the hydrogen bonding with water, ketones are highly soluble. Ketones generally have a strong scent, often pleasant and sweet, and may be used in perfumes. Like aldehydes, ketones are highly flammable, although they are generally both less reactive and less toxic than aldehydes.

Formation of Ketones

Ketones are generally formed via the oxidation of secondary alcohols, in the presence of a strong oxidising agent.

See Also

A guide to naming organic compounds : Functional Groups, ketosis