Structures of Racemic Halogen-Substituted 3-Hydroxy-3-phenylpropionic Acids; Relations Between Spontaneously Resolved and Racemic Compounds

Article abstract of DOI:10.1107/S0108768194011663

Low-temperature <122.0(5) K> X-ray diffraction data <λ(Cu Kα) = 1.54184 Angstroem> showed that racemic 3-hydroxy-3-(3'-chlorophenyl)propionic acid and its bromo-substituted analogue are isostructural. 3-Hydroxy-3-(3'-chlorophenyl)propionic acid: C9H9ClO3, M_r = 200.61, monoclinic, P2₁/c, a = 15.301 (2), b = 5.7117 (8), c = 11.2462 (13) Angstroem, β = 110.873 (10) deg, V = 918.4 (2) Angstroem³, Z = 4, D_x = 1.451 g cm^-3, μ = 35.15 cm^-1, F(000) = 416, wR₂ = 0.0775 for 1880 contributing reflections 4?(F)>, m.p. 342.7(5) K. 3-Hydroxy-3-(3'-bromophenyl)propionic acid: C9H9BrO3, M_r = 245.07, monoclinic, P2₁/c, a = 15.498 (3), b = 5.7513 (12), c = 11.298 (2) Angstroem, β = 111.280 (14) deg, V = 938.4 (3) Angstroem³, Z = 4, D_x = 1.735 g cm^-3, μ = 58.07 cm^-1, F(000) = 488, wR₂ = 0.0769 for 1926 contributing reflections 4?(F)>, m.p. 348.7(5) K.The results from these structure determinations were combined with results from crystal structure determinations of other halogen-substituted 3-hydroxy-3-phenylpropionic acids in an analysis performed to obtain insight into their conglomerate versus racemic compound formation.In all the structures studied, the O-H...O hydrogen bonds are formed between identical donor and acceptor atoms leading to two distinct motifs.The crystallization of the racemates as either racemic compounds or mechanical mixtures of enantiomers can only be rationalized if weaker intermolecular interactions are taken into account.