Carboxylic acids are carbonyl compounds in which one of the atoms or groups attached to the carbonyl C-atom is a hydroxyl group. The other group usually is a hydrocarbon group. The general formula of a carboxylic acid is R-CO-OH. The simplest carboxylic acid is formic acid, H-COOH. Note that formic acid also could be seen as an aldehyde but its chemistry is that of an acid. Acetic acid is shown. Note the position of the hydroxyl hydrogen atom. The COOH groups is planar and the hydroxyl H-atom is oriented toward the other O-atom.