IUPAC Nomenclature of Aldehydes and Ketones

The IUPAC names of open chain aliphatic aldehydes and ketones are derived from the names of the corresponding alkanes by replacing the ending -e with -al and -one respectively.

The following steps are followed:

a) The longest carbon chain containing the carbonyl carbon is taken to decide the name of the parent alkane.

b) The carbon chain is numbered from the end nearer to the carbonyl group and the substituents are prefixed in alphabetical order along with Arabic numerals including their positions in the carbon chain. The carbon of the aldehydic group and the carbonyl carbon in cyclic ketones always get the number 1.

c) When the aldehyde group is attached to a ring, the numbering of the ring carbon atoms starts from the carbon atom attached to the aldehyde group. The suffix carbaldehyde is added after the full name of the hydrocarbon.

The simplest aromatic aldehyde carrying the aldehyde group on a benzene ring is benzaldehyde.

Other ring substituted aromatic aldehydes are derivatives of benzaldehyde is ortho-hydroxy benzaldehyde.

The trivial names of aldehydes are derived from the trivial names of the corresponding carboxylic acids by replacing the ending ic, for acid with aldehyde. The positions of the substituents in the carbon chain are indicated by Greek letters a, b, g, d etc, the a-carbon being the one directly linked to the aldehyde group, the b-carbon the next and on.

Example:

The common names of ketones are derived by adding the names of the alkyl or aryl groups directly linked to the carbonyl group before the word ketone. The simplest ketone is acetone.

The positions of the substituents are indicated by the Greek letters a, a', b',b' and so on. a, a' carbons being the ones directly attached to the carbonyl group.

Examples:

Ketones with a carbonyl group attached to a benzene ring are named as phenones in the IUPAC.

Other examples of ketones

                                                                Common Name                                IUPAC Name

CH₃ — COCOCH₃                               Diacetyl                                                Butane-2, 3-dione

(CH₃)₂ — C = CH COCH₃                 Mesityl Oxide                    4-Methylpent-3-ene-2-one