Crystallographic rationalization of the reactivity and spectroscopic properties of (2R)-S-(2,5-dihydroxyphenyl)cysteine

At 150 K, the title compound, C9H11NO4S, crystallizes in the orthorhombic form as a zwitterion and has a low gauche conformation [chi = -46.23 (16)degrees] for an acyclic cysteine derivative. A difference in bond length is observed for the alkyl C-S bond [1.8299 (15) angstrom] and the aryl C-S bond [1.7760 (15) angstrom]. The -NH3+ group is involved in four hydrogen bonds, two of which are intermolecular and two intramolecular. The compound forms an infinite three-dimensional network constructed from four intermolecular hydrogen bonds. Characterization data (C-13 NMR, IR and optical rotation) are reported to supplement the incomplete data disclosed previously in the literature.