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Any of a class of organic compounds having a five-member ring composed of four carbon atoms and one nitrogen atom. The pyrrole ring structure is a component of many biologically important compounds, including porphyrins, alkaloids, and certain amino acids.

The simplest of this class of compounds, in which a single hydrogen atom is attached to each atom in the ring. It has a pleasant odor similar to that of chloroform. Chemical formula: C ₄ H ₅ N.