Carbonyl Compounds

Carbonyl Compounds

Introduction to Carbonyl Compounds

  • Carbonyl compounds contain the carbonyl functional group (-C=O), which consists of a carbon atom double-bonded to an oxygen atom.
  • The group includes aldehydes (R-CHO), ketones (R-CO-R’), carboxylic acids (R-COOH), esters (R-COOR’), and amides (R-CONR2).

Properties and Reactions of Carbonyl Compounds

  • Carbonyl compounds have high polarity due to the carbonyl group, leading to relatively high boiling points compared to hydrocarbons of similar size.
  • The polarity also means they are generally soluble in water and other polar solvents.
  • They act as nucleophiles and electrophiles, which make them highly reactive and able to undergo a variety of chemical reactions such as addition, reduction, and condensation.

Colour and Carbonyl Compounds

  • Carbonyl compounds typically absorb light in the UV region, but ones with extended systems of conjugated double bonds can absorb light in the visible region and therefore appear coloured.
  • This property is utilised in the creation of synthetic dyestuffs such as azo dyes and phthalocyanine dyes.

Tests for Carbonyl Compounds

  • The Brady’s test, also known as 2,4-dinitrophenylhydrazine test, can be used to detect the presence of a carbonyl group in a compound. A positive test results in a yellow-orange precipitate.
  • Tollens’ reagent, a clear, colourless solution of silver nitrate in ammonia, can be used to distinguish between aldehydes and ketones. Aldehydes are oxidised, forming a silver mirror on the test tube, whereas ketones do not react.
  • The Fehling’s test is another method to differentiate between aldehydes and ketones. Aldehydes reduce the blue Fehling’s solution to a red-brown precipitate, while ketones give no reaction.

Applications of Carbonyl Compounds

  • Carbonyl compounds are vital in the synthesis of many pharmaceuticals such as anti-inflammatory drugs, cholesterol-lowering statins, and β-lactam antibiotics.
  • They are also essential in the production of polymers such as polyesters and polyamides, as well as in the manufacture of adhesives, paints, and coatings.