Planar Carbon: Ketones

What are Ketones?

Ketones are organic compounds that contain a carbonyl group ($C=O$) bonded to two carbon atoms. Unlike aldehydes, where the carbonyl group is at the end of a carbon chain, in ketones, the carbonyl group is always located within the carbon chain.

Structure and Nomenclature of Ketones (Up to $C-4$)

• General Formula: Ketones have the formula $CₙH₂ₙO$. The simplest ketone is propanone.
• Naming Rules: In ketones, the carbonyl group ($C=O$) is not at the end of the chain, so the chain length and position of the carbonyl group must be indicated.
  • Propanone (acetone, $C₃H₆O$): The simplest ketone, with the carbonyl group on the second carbon.
  • Butan-2-one ($C₄H₈O$): A four-carbon chain with the carbonyl group on the second carbon.

Physical Properties of Ketones

• State: Lower ketones, such as propanone and butan-2-one, are liquids at room temperature.
• Solubility:
  • In water: Ketones are soluble in water due to their ability to form hydrogen bonds between the oxygen in the carbonyl group and water molecules.
  • In non-polar solvents: Ketones are also soluble in non-polar solvents like cyclohexane, due to interactions between their non-polar hydrocarbon chains and non-polar solvents.

Solubility of Propanone

• In water: Propanone (acetone) is highly soluble in water because of its ability to form hydrogen bonds with water molecules. This is due to the polar nature of the carbonyl group.
• In cyclohexane: Propanone is also soluble in cyclohexane, a non-polar solvent, because its non-polar carbon chain can interact with cyclohexane via van der Waals forces.

Use of Propanone as a Solvent

Propanone (acetone) is a widely used solvent in both industrial and household applications:

• Nail varnish remover: Propanone is an effective solvent for dissolving nail varnish and many types of plastics.
• Cleaning: It is also used for degreasing and cleaning purposes due to its ability to dissolve oils and other organic compounds.

Carboxylic Acids

Carboxylic acids are organic compounds containing a carboxyl group ($-COOH$). The carboxyl group consists of a carbonyl group ($C=O$) attached to a hydroxyl group ($-OH$). This structure makes carboxylic acids polar and capable of forming hydrogen bonds.

Structure Nomenclature of Carboxylic Acids (Up to $C-4$)

• Methanoic acid (formic acid, $HCOOH$): The simplest carboxylic acid with one carbon atom.
• Ethanoic acid (acetic acid, $CH₃COOH$): A two-carbon acid commonly found in vinegar.
• Propanoic acid ($C₃H₆O₂$): A three-carbon acid.
• Butanoic acid ($C₄H₈O₂$): A four-carbon acid with a strong, unpleasant smell.

Physical Properties of Carboxylic Acids

• State: Lower carboxylic acids like methanoic and ethanoic acid are liquids at room temperature, while higher acids may be solids.
• Solubility:
  • In water: Carboxylic acids are highly soluble in water because they can form strong hydrogen bonds due to their $-COOH$ group. Solubility decreases with increasing carbon chain length.
  • In non-polar solvents**:** Carboxylic acids are less soluble in non-polar solvents like cyclohexane, but still dissolve to some extent due to the non-polar hydrocarbon portion of the molecule.

Solubility of Ethanoic Acid

• In water: Ethanoic acid (acetic acid) is highly soluble in water, allowing it to form hydrogen bonds through its polar $-COOH$ group.
• In cyclohexane: Ethanoic acid is partially soluble in cyclohexane due to its non-polar carbon chain, though less soluble than in water.

Natural Sources and Uses of Carboxylic Acids

• Methanoic acid: Found in nettles and ants, where it acts as an irritant.
• Ethanoic acid (vinegar): Ethanoic acid is a key component of vinegar and is used in the manufacture of cellulose acetate, an important plastic material.
• Propanoic acid and benzoic acid: These acids, and their salts, are used as food preservatives to prevent bacterial growth.