Carbonyl as Substituent -On a molecule with a higher priority functional group,a ketone is an oxo and an aldehyde is a formyl group. Aldehydes have a higher priority than ketones. COOH 9 CH3 CH3-C-CH-CH2-C-H 43 CHO 3-methyl-4-oxopentanal 3-formylbenzoic acid Chapter 18 Chapter 18 7 Carbonyl as Substituent ▪ On a molecule with a higher priority functional group, a ketone is an oxo and an aldehyde is a formyl group. ▪ Aldehydes have a higher priority than ketones. 3-methyl-4-oxopentanal 3-formylbenzoic acid 4 3 1 1 3 CH3 C CH CH3 CH2 C H O O COOH CHO