Refinements of the crystal structures of DL-serine and anhydrous L-serine

The crystal structure of DL-serine has been refined on the basis of 964 independent reflections measured on an X-ray diffractometer. The refinement has converged to an R index of 0.032, with anisotropic temperature factors for all atoms including hydrogens. The resulting coordinates of the heavy atoms are in good agreement with those reported from an earlier neutron-diffraction study, and there is no indication of systematic differences in the C-C, C-N or C-O bond lengths. The structure of L-serine was refined to an R index of 0.059 for 953 reflections; the absolute configuration was confirmed from the anomalous scattering effects of C, N, and O. The final parameters include isotropic temperature factors for the H atoms. The conformations of the L-serine molecule in three different crystal structures are compared; differences in conformation are directly related to differences in the hydrogen-bond arrangements.