Oxygen or sulfur atoms

Full Title

Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom > with only hydrogen or carbon atoms directly attached to the ring nitrogen atom > having no double bonds between ring members or between ring members and non-ring members > with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms > Oxygen or sulfur atoms