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The crystal structure of the orthorhombic phase I of L-cysteine, C3H7NO2S, has been determined at 30 K. The molecule adopts a gauche+ conformation and the structure consists of zwitterions connected into sinusoidal layers by N—H
O hydrogen bonds. Further N—HO hydrogen bonds connect the structure into a three-dimensional array. Under ambient conditions, the thiol H atom is disordered in such a way as to form intermolecular S—HS and S—HO hydrogen bonds. At 30 K the structure is ordered with retention of the S—HS contacts [SS = 3.8489 (4) Å, S—HS = 2.66 (3) Å and S—HS = 150.8 (16)°].
O hydrogen bonds. Further N—HO hydrogen bonds connect the structure into a three-dimensional array. Under ambient conditions, the thiol H atom is disordered in such a way as to form intermolecular S—HS and S—HO hydrogen bonds. At 30 K the structure is ordered with retention of the S—HS contacts [SS = 3.8489 (4) Å, S—HS = 2.66 (3) Å and S—HS = 150.8 (16)°].
