Penicillins structure consists of a side chain (a benzyl group and an amide carbonyl) and a 6-Aminopenicillanic acid nucleus (a b-Lactam ring and a Thiazolidone ring). The b-Lactam ring is not found in any other natural product and is highly strained and thus readily hydrolyzed, this makes penicillin very reactive towards acid and alkali conditions. The diagram shows penicillin G or benzylpenicillin because of the benzyl side chain. Yet penicillin's can differ by the changing of the side chain which is attached to the amide carbonyl.

      3D model of penicillin