**As of Feb 2020 IUPAC recognizes “oxo” as a prefix for aldehyde groups in polyfunctional compounds. Formyl- is still accepted. The differentiation is that formyl- is used if carbaldehyde would be used (like hanging off a ring) and oxo- is used if the aldehyde group is linear.
Aldehydes and Ketones: Nomenclature Answers
4-ethyl-5-methyloctanal
3-n-butyloctanal (or 3-butyloctanal)
6-isopropyl-7-decen-5-one
6-hydroxy-5-methyl-2-hexanone
2,7-octanedione
9-hydroxy-6-oxononanal
3-pentylcyclohexanone
7-hydroxy-3-octenal
4-[2,2-dimethylpropyl]cyclohexanone
1,3-cyclohexanedione
3-[3-hydroxypentyl]cyclohexanone
1-cyclopentyl-2-hexanone
2-[3-oxobutyl]cyclopentanone
2-[1-bromopropyl]hexanal