In organic chemistry, functional groups are specific groups of atoms within molecules that have distinct chemical properties and reactivity. Understanding functional groups is crucial for predicting the behavior of organic compounds. Consider the following compounds:
1. CH3-COOH
2. CH3-CH2-NH2
3. CH3-C(C2H5)=O
4. CH3-C2H4-Br
Which of these compounds contains a carboxylic acid functional group?