Organic Families - Carbonyls (DP IB Chemistry: SL)

• Carbonyl is the collective name for compounds containing the functional group C=O
• The general formula of a carbonyl is C_nH_2nO
• The two sub-families of carbonyls are aldehyde and ketone (known in some countries as alkanals and alkanones)

Aldehydes

• If the carbonyl group is on the end of a chain then it is an aldehyde and has the functional group formula, RCHO
  • the H is written before the O so as not to confuse it with an alcohol

• The nomenclature of carbonyls follows the pattern alkan + al
• There is no need to use numbers in the name as aldehyde will always be on the number 1 carbon atom

Ketones

• Ketones have a minimum of three carbons and have the general functional group formula, RCOR
• The nomenclature of ketones follows the pattern alkan + one
• After butanone, the carbonyl group can have positional isomers, so numbering must be used
  • For example pentan-2-one and pentan-3-one

Aldehyde and Ketone Examples Table

• As they have a very similar functional group arrangement, aldehydes and ketones show similar chemical reactions
• Differences in their chemistry are due to the reactions that involve the H on the aldehyde or the nature of the R group
• The difference in electronegativity between oxygen and carbon means the C=O is polar, leading to dipole-dipole attractions between the molecules which results in:
  • higher than expected boiling points for small molecules
  • solubility in water for the lower members of the families
• Aldehydes and ketones with the same number of carbons are functional group isomers