Nomenclature of Aldehydes and Ketones

What are Aldehydes and Ketones?

The chemistry of aldehydes and ketones is influenced by the presence of a carbonyl group in them. In aldehydes, the carbonyl group is attached to a carbon and hydrogen, whereas in ketones it is bonded to two carbon atoms.

Nomenclature of Aldehydes and Ketones

In other words, the two remaining bonds of the carbon atom in the carbonyl group are taken by hydrogen, alkyl or aryl substituents. If one of the substituents is hydrogen then the compound is called aldehyde and if none of them is hydrogen then it is a ketone.

Naming Aldehydes

• According to the IUPAC system of nomenclature -al is attached as a suffix to parent alkane for the naming of aldehydes.
• For example, H2C=O is named as per the IUPAC system as methanal, commonly known as formaldehyde.
• The aldehyde group is always attached at the end of the main carbon chain, and hence the 1st  position in the numbering is always assigned to it. It is not always necessary to include numbering in the naming.
• Instead of IUPAC name aldehydes and ketones are also called by their common names.
• For aldehydes and ketones, the names are reflected in Greek and Latin term. Greek letters such as α, β etc. are used for the location of the substituents in the carbon chain.
• The α-carbon is directly attached to the aldehyde group, β-carbon is attached to the carbon adjacent to the aldehyde group and so on.

Naming Ketones

• Now let’s discuss the naming of ketones, according to IUPAC guidelines, the suffix –one is assigned for the ketones.
• The carbonyl group can be located anywhere within the main chain and the position is decided by the location number.
• The numbering of the chain usually starts from the end such that the carbonyl carbon gets the lowest number.
• But there are some ketones such as propanone and phenylethanoid which do not require any number locator as there is only one possible site for ketone carbon.

If there are more than one functional groups in a molecule then the functional group with the higher priority is named first and the other ones are considered as a substituent. If there is both a ketone and aldehyde group in a molecule then the aldehyde group is given priority over ketone while naming.