Ball-and-stick model of an amoxicillin molecule, C₁₆H₁₉N₃O₅S, as found in the crystal structure of the trihydrate, reported in Acta Cryst. B (1978) 34, 461-466 (CSD entry AMOXCT10). The COOH and NH₂ groups have reacted to form a zwitterion, i.e. COO⁻ and NH₃⁺. The phenol OH hydrogen is not located in the crystal structure determination but is assumed to be present. It is omitted in this diagram.

Colour code:

  Carbon, C: grey

  Hydrogen, H: white

  Nitrogen, N: blue

  Oxygen, O: red

  Sulfur, S: yellow