The self-assembly and spontaneous resolution of a hydrogen-bonded helix

Although geometrically similar at the single-molecule level, the crystal structures of 2,2′-dipyrrolyl ketone and its synthetic precursor, 2,2′-dipyrrolyl thioketone, vary greatly at the supramolecular level: the ketone self-assembles via hydrogen bonding into supramolecular helices accompanied by a spontaneous resolution process to generate homochiral crystals, whereas the thioketone assembles into non-helical and racemic crystals composed of layers of alternating enantiomers held together by weak interactions.