When multiple functional groups are present, the one with the highest priority (lowest number in this table) determines the suffix. All lower-priority groups are expressed as prefixes.

Priority	Functional Group	Suffix	Prefix (when not principal)
1	Carboxylic acid	-oic acid	carboxy-
2	Ester	-oate	(alkoxy-carbonyl-)
3	Amide	-amide	carbamoyl-
4	Aldehyde	-al	oxo- (on terminal carbon)
5	Ketone	-one	oxo-
6	Alcohol	-ol	hydroxy-
7	Amine	-amine	amino-
8	Alkyne	-yne	—
9	Alkene	-ene	—
10	Alkane	-ane	—

Note on aldehydes: The carbonyl carbon of an aldehyde is always C-1, so no locant is needed in the name (e.g., propanal, not propan-1-al).

Note on carboxylic acids: Similarly, the carboxyl carbon is always C-1.

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