(2S,4R)-4-Ammonio-5-oxopyrrolidine-2-carboxylate

In the crystal structure of the title compound, C(5)H(8)N(2)O(3), the mol-ecules exist in the zwitterionic form. The pyrrolidine ring adopts an envelope conformation with the unsubstituted endocyclic C atom situated at the flap. The other four endocyclic atoms are coplanar with the exocyclic carbonyl O atom, with an r.m.s. deviation from the mean plane of 0.06 Å. The carboxyl-ate substituent is located axially, while the ammonium group occupies an equatorial position. In the crystal structure, the mol-ecules are linked through N-H⋯O hydrogen bonds, forming a three-dimensional network.