Physical Properties of Aldehydes and Ketones

Physical Properties of Aldehydes and Ketones

Carbonyl Compounds

The compounds containing carbon-oxygen double bond in them are termed carbonyl compounds.

Aldehydes and ketones are the class of organic compounds that have a carbonyl group i.e. carbon-oxygen double bond (-C=O). As they do not have any other reactive groups like –OH or -Cl attached to the carbon atom in the carbonyl group they are very simple compounds.  The chemistry of aldehydes and ketones is greatly influenced by the presence of the carbonyl group.

Table of Contents

Physical Properties of Aldehydes and Ketones:

Boiling point: The boiling point of methanal is -19 o C and for ethanal it is +21 o C. From this, we can say that the boiling point of ethanal is close to room temperature. Generally, the boiling point of aldehydes and ketones increases with an increase in molecular weight. This is because the boiling point depends upon the strength of the intermolecular forces.

  • Vander Waals dispersion forces:As the molecules get longer and the number of electrons increases, which results in the increase in the magnitude of van der Waal forces. Therefore, for this reason, the boiling point of both aldehydes and ketones increases with the increase in the number of carbon atoms.
  • Vander Waals dipole-dipole attraction:Because of the presence of carbon-oxygen double bond both aldehydes and ketones are polar in nature. Thus, there will be an attraction between permanent dipoles present in aldehydes and ketones as well as the molecules which are near them. This is the reason for aldehydes and ketones having boiling points higher than similar-sized hydrocarbons.

Solubility: Aldehydes and ketones are soluble in water but their solubility decreases with an increase in the length of the chain. Methanal, ethanal and propanone are those aldehydes and ketones which are of small size and are miscible with water in almost all proportions.

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Aldehydes and ketones cannot form hydrogen bonds with themselves, but they can have hydrogen bonds with  water molecules and this forms the basis for good solubility of aldehydes and ketones in water.

Uses of aldehydes and ketones

Aldehydes and ketones find many applications in different industries. They are extensively used in the manufacturing of polymers, blending of perfumes and also as flavouring agents.

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