You need to know the chemical structure of amoxicillin. You can do a google search for the strucure and from the structure you can determine the functional groups present. The result from my goole search yields:
1. phenol (OH attached to benzene ring)
2. amine (primary: -NH2)
3. ketone (C=O)
4. carboxyclic acid (COOH)
5. amide
6. thioether (C-S-C)