(a) L-Serine-II at 5.2 GPa and (b) L-serine-III at 8.1 GPa as viewed along c. A and B layers as referred to in the text are labelled. 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, CD⋯O interactions are shown in the top-left corner only. Note the formation of the O1D7⋯O1 interaction in L-serine-III at 8.1 GPa. The colour scheme is the same as in Fig. 3.