ams ▁are ▁class ified ▁according ▁to ▁their ▁core ▁ring ▁structures . ▁ β - la ct ams ▁f used ▁to ▁s atur ated ▁five - member ed ▁rings : ▁ β - la ct ams ▁containing ▁th ia z olid ine ▁rings ▁are ▁named ▁pen ams . ▁ β - la ct ams ▁containing ▁p yr rol id ine ▁rings ▁are ▁named ▁car b ap en ams . ▁ β - la ct ams ▁f used ▁to ▁ox az olid ine ▁rings ▁are ▁named ▁ox ap en ams ▁or ▁cla v ams . ▁ β - la ct ams ▁f used ▁to ▁uns atur ated ▁five - member ed ▁rings : ▁ β - la ct ams ▁containing ▁ 2 , 3 - d ih ydro th ia z ole ▁rings ▁are ▁named ▁pen ems . ▁ β - la ct ams ▁containing ▁ 2 , 3 - d ih ydro - 1 H - py r role ▁rings ▁are ▁named ▁car b ap en ems . ▁ β - la ct ams ▁f used ▁to ▁uns atur ated ▁six - member ed ▁rings : ▁ β - la ct ams ▁containing ▁ 3 , 6 - d ih ydro - 2 H - 1 , 3 - th ia z ine ▁rings ▁are ▁named ▁ce ph ems . ▁ β - la ct ams ▁containing ▁ 1 , 2 , 3 , 4 - t et rah yd ropy rid ine ▁rings ▁are ▁named ▁car b ace ph ems . ▁ β