What functional group does a carboxylic acid contain?
Carboxylic acids are organic molecules that contain a carbon atom that is double bonded to an oxygen atom. This group is called a carbonyl. In a carboxylic acid, the carbon of the carbonyl group is also single bonded to a hydroxy group and an R group, which may be either a hydrogen atom, an alkyl group, or an aryl group. There are several other types of organic molecules that contain either a carbonyl group or a hydroxy group. But in order to be classified as a carboxylic acid, a hydroxy group must be bonded to the carbon atom of a carbonyl group.
The combination of a carbonyl group and a hydroxy group forms the functional group, a carboxyl, which is the primary functional group of a carboxylic acid. We can represent a carboxyl group using a structural formula like the one shown here, but we can also represent this group using a displayed formula. In the displayed formula of a carboxyl group COOH, both the carbonyl portion and the hydroxy portion are represented. We may even include a dash in front of the displayed formula. The dash indicates that the carbon atom of the carboxyl group connects to or bonds to an R group.
So the functional group that a carboxylic acid contains is a carboxyl group, which can be represented by dash COOH.