Carbonyl compounds are named using IUPAC rules, based on the longest carbon chain that contains the C=O group.Aldehydes use the suffix -al. The carbonyl carbon is always at the end of the chain, so it is always carbon 1 and no number is needed.
• HCHO: methanal
• CH3CHO: ethanal
• CH3CH2CHO: propanal
• CH3CH2CH2CHO: butanalKetones use the suffix -one. The chain is numbered from the end that gives the carbonyl carbon the lowest number, and this number goes before -one when it is needed.
• CH3COCH3: propanone (the C=O can only be on carbon 2)
• CH3COCH2CH3: butanone (again only one possible position)
• CH3COCH2CH2CH3: pentan-2-one
• CH3CH2COCH2CH3: pentan-3-oneBranches are named as prefixes, numbered from the end that gives the C=O the lowest number (for aldehydes, from the CHO carbon).Worked example 1: (CH3)2CHCHO. The longest chain containing the CHO has 3 carbons, with a methyl group on carbon 2. Name: 2-methylpropanal.Worked example 2: CH3COCH(CH3)CH3. The longest chain has 4 carbons; numbering from the left puts the C=O on carbon 2 and the methyl on carbon 3. Name: 3-methylbutan-2-one.In structural formulae, write an aldehyde group as CHO, never COH, which could be confused with an alcohol. A ketone group within a chain is written CO.
• HCHO: methanal
• CH3CHO: ethanal
• CH3CH2CHO: propanal
• CH3CH2CH2CHO: butanalKetones use the suffix -one. The chain is numbered from the end that gives the carbonyl carbon the lowest number, and this number goes before -one when it is needed.
• CH3COCH3: propanone (the C=O can only be on carbon 2)
• CH3COCH2CH3: butanone (again only one possible position)
• CH3COCH2CH2CH3: pentan-2-one
• CH3CH2COCH2CH3: pentan-3-oneBranches are named as prefixes, numbered from the end that gives the C=O the lowest number (for aldehydes, from the CHO carbon).Worked example 1: (CH3)2CHCHO. The longest chain containing the CHO has 3 carbons, with a methyl group on carbon 2. Name: 2-methylpropanal.Worked example 2: CH3COCH(CH3)CH3. The longest chain has 4 carbons; numbering from the left puts the C=O on carbon 2 and the methyl on carbon 3. Name: 3-methylbutan-2-one.In structural formulae, write an aldehyde group as CHO, never COH, which could be confused with an alcohol. A ketone group within a chain is written CO.