Carbonyl compounds (Aldehydes and ketones) physical and chemical properties

Carbonyl compounds Definition

• Carbonyl compounds are organic compounds that contain a carbonyl group (C=O) as their functional group.
• The two major classes are:

Physical Properties

1. Molecular Structure:

   • The carbonyl group consists of a carbon atom double-bonded to an oxygen atom, creating a site of high electron density.
   • In aldehydes, the carbonyl group is bonded to a hydrogen atom and an alkyl or aryl group. In ketones, it is bonded to two alkyl or aryl groups.

2. Polarity:

   • The carbon-oxygen bond is highly polar due to the electronegativity difference between the atoms, resulting in a significant dipole moment.

3. Boiling Points:

   • Aldehydes and ketones have higher boiling points than hydrocarbons of similar molecular weight due to dipole-dipole interactions.
   • Their boiling points are lower than alcohols and carboxylic acids, as they cannot form hydrogen bonds as effectively.

4. Solubility:

   • They are generally soluble in organic solvents and somewhat soluble in water.
   • Lower molecular weight aldehydes and ketones are more water-soluble because they can form hydrogen bonds with water molecules.

Chemical Properties

1. Nucleophilic Addition:

   • The electrophilic carbon in the carbonyl group is susceptible to attack by nucleophiles.
   • This forms the basis of many reactions, such as with amines, hydrides, and cyanides.

2. Oxidation and Reduction:

   • Aldehydes are easily oxidized to carboxylic acids by oxidizing agents like KMnO₄ or K₂Cr₂O₇.
   • Ketones are more resistant to oxidation but can be reduced to alcohols using reducing agents like NaBH₄ or LiAlH₄.

3. Formation of Hemiacetals and Acetals:

   • Aldehydes and ketones can react with alcohols to form hemiacetals and acetals under acid catalysis.

4. Aldol Condensation:

   • Aldehydes and ketones can undergo aldol condensation in the presence of a base or acid, forming β-hydroxy aldehydes or ketones.

5. Cannizzaro Reaction:

   • Aldehydes without an α-hydrogen undergo the Cannizzaro reaction with strong bases, producing a mixture of a carboxylic acid and an alcohol.

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