In compounds which contain a carbonyl group, the parent is the longest chain containing the carbonyl carbon.

For an aldehydethe parent alkane -> alkanal; the chain is numbered beginning with the carbonyl carbon as #1.

If the carbonyl carbon of an aldehyde is attached to a ring, the compound is a cycloalkane carbaldehyde, and the carbon of the ring to which the aldehyde is attached is #1.

For a ketone the parent alkane -> alkanone; the chain is numbered beginning from the end closest to the carbonyl carbon.If the carbonyl carbon is the same distance from each end, number from the end closest to the first substituent.

If the carbonyl carbon of a ketone is part of a ring, the compound is a cycloalkanone, and the carbonyl carbon is #1.

If the carbonyl carbon of a ketone is attached to a ring, the compound may be named as an alkyl alkyl ketone; list the two alkyl groups attached to the carbonyl carbon in alphabetical order.

If two ketone groups are present, it’s a dione:

If a C=C is present, the compound is an alkenal or alkenone, and the position of the carbonyl still determines how the compound is numbered.

Priorities: an aldehyde or ketone takes priority over an -OH (a hydroxy group), etc.A carbonyl as a substituent is an oxo group.Hence: