Abstract
Halogenated carboxylic acids have been important compounds in chemical synthesis and indispensable research tools in biochemical studies for decades. Nevertheless, the number of structurally characterized simple α-brominated monocarboxylic acids is still limited. We herein report the crystallization and structural elucidation of (R)- and rac-2-bromo-3-methylbutyric acid (2-bromo-3-methylbutanoic acid, 1) to shed light on intermolecular interactions, in particular hydrogen bonding motifs, packing modes and preferred conformations in the solid-state. The crystal structures of (R)- and rac-1 are revealed by X-ray crystallography. Both compounds crystallize in the triclinic crystal system with Z = 2; (R)-1 exhibits two crystallographically distinct molecules. In the crystal, (R)-1 forms homochiral O–H···O hydrogen-bonded carboxylic acid dimers with approximate non-crystallographic C2 symmetry. In contrast, rac-1 features centrosymmetric heterochiral dimers with the same carboxy syn···syn homosynthon. The crystal packing of centrosymmetric rac-1 is denser than that of its enantiopure counterpart (R)-1. The molecules in both crystal structures adopt a virtually identical staggered conformation, despite different crystal environments, which indicates a preferred molecular structure of 1. Intermolecular interactions apart from classical O–H···O hydrogen bonds do not appear to have a crucial bearing on the solid-state structures of (R)- and rac-1.
Highlights
Halogenated organic compounds have received considerable research interest for decades, in the field of chemical synthesis [1,2,3] and because of their biological properties [4,5]
The crystal structures of (R)- and rac-1 are revealed by X-ray crystallography
The absolute configuration of (R)-1 was confirmed by means of anomalous dispersion effects in the diffraction intensity measurements
Summary
Halogenated organic compounds have received considerable research interest for decades, in the field of chemical synthesis [1,2,3] and because of their biological properties [4,5]. A vast number of halogenated carboxylic acids have been synthesized and biochemically studied. Since mono-, di- and tricarboxylic acids are important intermediates in many biochemical pathways, their halogenated analogues have become an important research tool for the study of a wide range of biological processes owing to their ability to imitate the properties of the respective carboxylic acids or to inhibit crucial enzymes [6,7]. Despite tremendous research interest in halogenated carboxylic acids, the number of crystal structures of simple α-brominated monocarboxylic acids in the Cambridge Structural Database (CSD) is limited (13 as of June 2020) [8]. An example is bromoacetic acid, which forms a common syn···syn hydrogen-bonded carboxy dimer (Scheme 1) in the crystal (CSD refcode: BRMACA) [9].
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.