The structure of dl-histidine, C 6 H 9 N 3 O 2 , has been determined from three-dimensional X-ray diffraction data and refined until R = 0.13 and standard deviations in bond lengths are ∼ 0.005 Å. The crystals are monoclinic, P 2 1 / c , with a = 8.983, b = 8.087, c = 9.415 Å, β = 97.65°. The histidine molecule is nearly fully extended but the conformation is not the same as that of the chemically identical histidine molecules in crystalline L-histidine.
