Aldehydes and Ketones
Aldehydes and ketones are the simplest and most important carbonyl compounds.
There are two systems of nomenclature of aldehydes and ketones.
Common names of aldehydes:
The common names of aldehydes are derived from the common names of the corresponding carboxylic acids in which the ending ‘-ic’ is replaced with ‘-aldehyde’of acid with the aldehyde. For example:
IUPAC names of aldehydes:
In IUPAC system, the suffix ‘e’ of the alkane is replaced by the ‘al’.
Common names of ketones:
The common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group.
Alkyl phenyl ketones are usually named by adding the acyl group as a prefix to phenone. For example:
IUPAC name of ketones:
In IUPAC system, the suffix ‘e’ of the alkane is replaced by the ‘one’. For example:
Structure of the Carbonyl Group
- The carbonyl carbon atom is sp2-hybridised and forms three sigma (σ) bonds. The fourth valence electron of carbon remains in its p-orbital and forms a π-bond with oxygen by overlap with p-orbital of an oxygen.
- In addition, the oxygen atom also has two non-bonding electron pairs. Thus, the carbonyl carbon and the three atoms attached to it lie in the same plane and the π-electron cloud is above and below this plane.
- The high polarity of the carbonyl group is explained on the basis of resonance involving a neutral (A) and a dipolar (B) structures.
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