Aldehydes and Ketones: Structure, Properties, and Reactions
Expert reviewed •23 November 2024• 5 minute read
The carbonyl group (C=O) is a key feature in organic chemistry, appearing in several important functional groups. This article explores two major carbonyl-containing compounds: aldehydes and ketones.
Structure and Bonding
Aldehydes and ketones both contain a carbonyl group (C=O), where the carbon atom is sp² hybridized. The main difference between these compounds lies in their molecular structure:
Aldehydes: The carbonyl carbon is bonded to at least one hydrogen atom
Ketones: The carbonyl carbon is bonded to two carbon groups
The C=O bond consists of:
One σ bond (strong and unreactive)
One π bond (weaker and responsible for reactivity)
Nomenclature
Aldehydes
Suffix: -al
Prefix: formyl-
Example: CH₃CH₂CHO (propanal)
Ketones
Suffix: -one
Prefix: oxo-
Example: CH₃COCH₃ (propanone)
When naming compounds with multiple functional groups, priority follows this order:
Aldehydes
Ketones
Alcohols
Alkenes
Alkynes
Alkanes
Physical Properties
Intermolecular Forces
Both aldehydes and ketones are polar molecules due to the electronegative oxygen atom. They can form:
Dipole-dipole interactions
Van der Waals forces (dispersion forces)
Hydrogen bonds with water (but not with themselves)
Boiling and Melting Points
Higher than equivalent hydrocarbons due to stronger intermolecular forces
Lower than equivalent alcohols (which can form hydrogen bonds)
Increase with molecular mass within each homologous series
Water Solubility
Small molecules are water-soluble due to hydrogen bonding with water
Solubility decreases as carbon chain length increases
More polar than hydrocarbons but less polar than alcohols
Oxidation Reactions
Aldehydes
Can be oxidized to carboxylic acids
Common oxidizing agents include:
Acidified potassium permanganate (H⁺/KMnO₄)
Tollens' reagent (Ag(NH₃)₂⁺)
Jones reagent (CrO₃/H⁺)
Ketones
Cannot be oxidized under normal conditions
The carbon adjacent to the carbonyl group has no hydrogen atoms