Basic forms of supramolecular self-assembly organized by parallel and antiparallel hydrogen bonds in the racemic crystal structures of six disubstituted and trisubstituted cyclopentane derivatives

A selection of stereoisomeric 2-hydroxy-1-cyclopentanecarboxamides, a 4-ter t-butyl derivative and three tert-butyl derivatives of the respective carbo xylic acid were subjected to X-ray crystallography. The optically active mo lecules (I)(VI) form racemic crystals. Each racemic structure is basically determined by two intermolecular hydrogen bonds of O-H . . .O=C-XH and O=C- X-H . . . OH types (X = O, NH). The partially similar patterns of close pac king observed reflect five basic forms of supramolecular self-assembly. In the racemic crystals of chiral molecules, there are homo- and heterochiral chains of molecules formed by the principal (O-H . . .O=C) hydrogen bonds. These chains assemble either in a parallel or antiparallel mode. The parall el homochiral chains (hop) observed in structure (II), (1R*,2R*)-2-hydroxy- 1-cyclopentanecarboxamide, demand the polar space group Pca2(1), while the parallel heterochiral chains (hep) are organized in antiparallel layers wit h space group P2(1)/n in structure (VI), (1R*,2S*,5R*-5-tert-butyl-2-hydrox y-1-cyclopentanecarboxylic acid). Heterochiral chains in an antiparallel ar ray (hea) are found in (I), (1R*,2S*)-2-hydroxy-1-cyclopentanecarboxamide, and (V) [(1R*,2S*4S*)-4-tert-butyl-2-hydroxy-1-cyclopentanecarboxylic acid, space group P2(1)/c]. Structures (IV), (1R*,2S*,4R*)-4-tert-butyl-2-hydrox y-1-cyclopentanecarboxylic acid, and (III), (1R*,2R*,4S*)-4-tertbutyl-2-hyd roxy-1-cyclopentanecarboxamide reveal that homochiral chains in an antipara llel array (hoa; cross-linked by heterochiral dimers held together by the s econd hydrogen bonds) can be formed by either translation (space group Pi) or a screw axis (space group P2(1)/c). These alternatives are denoted hoa1 and hoa2. Similarly, within each pattern (hea. hep and hop) two slightly di fferent alternatives can be expected. The partial similarities in the ident ified five patterns of hydrogen bonding are described by graph-set notation s. Structures (I), (IV) and (V) can be characterized by a common supramolec ular synthon, while the highest degree of similarity is shown by the isostr ucturality of (I) and (V).