Carbonyl compounds are named from the longest carbon chain containing the C=O group.Aldehydes use the suffix -al. The CHO carbon is always carbon 1, so no position number is needed for the carbonyl group:
• HCHO methanal
• CH3CHO ethanal
• CH3CH2CHO propanal
• CH3CH2CH2CHO butanalSide chains are numbered from the CHO carbon, so (CH3)2CHCHO is 2-methylpropanal.Ketones use the suffix -one. The chain is numbered to give the carbonyl carbon the lowest possible number, and the number goes before -one when it is needed:
• CH3COCH3 propanone (the simplest ketone, three carbons)
• CH3COCH2CH3 butanone (no number needed, the C=O can only be on carbon 2)
• CH3COCH2CH2CH3 pentan-2-one
• CH3CH2COCH2CH3 pentan-3-oneA ketone must have at least three carbons, because the carbonyl carbon needs a carbon on each side.Worked example: name CH3CH2COCH2CH2CH3. The chain has six carbons (hexan-). Numbering from the left puts the C=O on carbon 3; from the right it would be carbon 4, so use 3. The name is hexan-3-one.
• HCHO methanal
• CH3CHO ethanal
• CH3CH2CHO propanal
• CH3CH2CH2CHO butanalSide chains are numbered from the CHO carbon, so (CH3)2CHCHO is 2-methylpropanal.Ketones use the suffix -one. The chain is numbered to give the carbonyl carbon the lowest possible number, and the number goes before -one when it is needed:
• CH3COCH3 propanone (the simplest ketone, three carbons)
• CH3COCH2CH3 butanone (no number needed, the C=O can only be on carbon 2)
• CH3COCH2CH2CH3 pentan-2-one
• CH3CH2COCH2CH3 pentan-3-oneA ketone must have at least three carbons, because the carbonyl carbon needs a carbon on each side.Worked example: name CH3CH2COCH2CH2CH3. The chain has six carbons (hexan-). Numbering from the left puts the C=O on carbon 3; from the right it would be carbon 4, so use 3. The name is hexan-3-one.