Nomenclature


(i) Aldehydes:

In aldehydes C of carbonyl group is attached to one alkyl group and one H.

  • In IUPAC system of nomenclature C of aldehyde is given in number if it is included in the longest continuous chain.
  • The suffix –e of the parent hydrocarbon is replaced by –al.

  • If —CHO group is attached to a cyclic chain, carbaldehyde is written as a suffix to the parent hydrocarbon.

  • If —CHO group is attached to benzene ring it is written as benzaldehyde.

(ii) Ketones:

  • In Ketones C of carbonyl group is given lowest number in the longest C-chain.
  • The suffix ‘e’ of the parent hydrocarbon is replaced by ‘one’.

If more than one carbonyl groups are present, the nomenclature of the compound is done in following way:

Structure of the Carbonyl Group

The carbonyl C is sp2 hybridised and forms three σ-bonds. Fourth electron of carbon atom remains in unhybridised p-orbital and form π bond with oxygen by overlapping with p-orbital of oxygen. Carbon and three atoms attached to it lie in the same plane and form a trigonal coplanar structure.

  • Carbonyl group is polar due to high electronegativity of oxygen atom.

  • Carbonyl compounds have higher polarity than ethers due to the presence of above structures.