(a) L-Serine-I at 4.6 GPa, (b) L-serine-II at 5.2 GPa and (c) L-serine-III at 8.1 GPa as viewed along b. ring motifs are shown. ND⋯O and OD⋯O hydrogen bonds are drawn as black dotted lines, while CD⋯O interactions are drawn as orange dotted lines. For clarity, the bifurcated interaction N1D5⋯O1/O2 and CD⋯O interactions are shown in the top-left corner only. These layers are referred to as the B layers in the text. The colour scheme is the same as in Fig. 3.