Ketone

Ketones have a carbonyl group (C=O) which is not at the end of a carbon chain. This means that they have the general formula, RCOR' (where R and R' represents any group of carbon and hydrogen atoms).

The simplest ketone is propanone (old name acetone). This is a useful solvent and is sometimes used as a nail varnish remover. Other ketones include cyclohexanone, and butane-2,3-dione which is a spoiling flavour in beer. Ketones are excreted in the urine of diabetics when fats are broken down for energy.

Ketone test tablets for diabetes

Ketones can be prepared by the oxidation of a secondary alcohol. They are not readily oxidized, so do not react with Fehling's solution or Benedict's solution.

Nomenclature

Ketones are given the suffix -ONE (pronounced "own"), giving names of the type alkanone . A number is usually needed here to identify the position of the group (unless there is only one possible position to place the C=O other than on the end).

Examples

The structural formula is CH₃COCH₃.

It is called propanone. There is no need for a number as the carbonyl group can only be in this place. If it were on the end it would be an aldehyde called propanal. However, you will probably not lose any credit if you do describe it as propan-2-one.

This time a number is needed as the carbonyl group could be in either positions 2 or 3. With 5 carbons, and counting to give the smallest number, this molecule is pentan-2-one.

This is a cyclic ketone with five carbon atoms in it. It is called cyclopentanone. Unless there is another side group, there is no need for a number as all the positions are equivalent.

The structural formula is CH₃COCH₂COCH(CH₃)₂

This has two ketone functional groups and one methyl side chain. All need to be numbered correctly. Its name is 2-methylhexane-3,5-dione. As the d prevents a vowel clash we don't need to lose the e on the end of hexane.

Reactions

See the practical of Unit 4.