Crystal structures of three β-halolactic acids: hydrogen bonding resulting in differing Z'

The crystal structures of three β-halolactic acids have been determined, namely, β-chlorolactic acid (systematic name: 3-chloro-2-hydroxypropanoic acid, C₃H₅ClO₃) (I), β-bromolactic acid (systematic name: 3-bromo-2-hydroxypropanoic acid, C₃H₅BrO₃) (II), and β-iodolactic acid (systematic name: 2-hydroxy-3-iodopropanoic acid, C₃H₅IO₃) (III). The number of molecules in the asymmetric unit of each crystal structure (Z') was found to be two for I and II, and one for III, making I and II isostructural and III unique. The difference between the molecules in the asymmetric units of I and II is due to the direction of the hydrogen bond of the alcohol group to a neighboring molecule. Molecular packing shows that each structure has alternating layers of intermolecular hydrogen bonding and halogen-halogen interactions. Hirshfeld surfaces and two-dimensional fingerprint plots were analyzed to further explore the intermolecular interactions of these structures. In I and II, energy minimization is achieved by lowering of the symmetry to adopt two independent molecular conformations in the asymmetric unit.