Acetyl isnt a type of functional group, it is a specific substutuent, the -C=O-CH3 substituent.
Acetylacetone is a molecule of acetone where one H is replaced by a an acetyl substituent.
Formic acid, acrolein and acroleic acid are compounds, you can look up the structures online. The acryl substituent derives from acrolein.
Acetyl isnt a type of functional group, it is a specific substutuent, the -C=O-CH3 substituent. Acetylacetone is a molecule of acetone where one H is replaced by a an acetyl substituent. Formic acid, acrolein and acroleic acid are compounds, you can look up the structures online. The acryl substituent derives from acrolein.
Unconventional conventions. IUPAC isn’t always used because the names are sometimes too long.
Try to go over some common iupac rules for naming organic compounds. It will help you understand better
They were the names for these groups before iupac existed I think, and it’s just never gone away completely