Introduction to Alkanones
Alkanones are also commonly referred to as ketones.
For example, propan-2-ol can be oxidised to propanone (an alkanone also known as acetone) by heating it with a few drops of acidified sodium dichromate(VI) solution until the colour of the solution changes from orange to green.
Structure of Alkanones
Alkanones are similar in structure to alkanes. However, on one of the carbons, two of the hydrogens have been replaced by an oxygen. For examle, the alkanone containing three carbon atoms is shown below.H O H | || | H - C - C - C - H | | H H
Alkanones are named as follows:
- The number of carbon atoms in the longest carbon chain is noted
- The corresponding alkane is then named
- Finally, the name of this alkane is modified by removing the ane and replacing it with anone
- If there are more than four carbon atoms in the longest carbon chain of the alkanone, then the anone is replaced with an-n-one where n is the number of the carbon atom to which the oxygen is bonded
Therefore, the alkanone shown above contains three atoms in the longest carbon atom chain. The corresponding alkane is propane. The ane is replaced by anone to give the alkanone its name: propanone.
Reactions of Alkanones
Alkanones, unlike alkanals, cannot be further oxidised. Therefore, they do not react with Benedict's solution. An alkanone can be distinguished from an alkanal by trying to react the unknown compound with Benedict's solution. If it reacts; it is an alkanal, if not it is an alkanone.