Conformational Preference of 2'-Fluoro-Substituted Acetophenone Derivatives Revealed by Through-Space ¹H-¹⁹F and ¹³C-¹⁹F Spin-Spin Couplings.

ABSTRACT: The conformational properties of 2'-fluoro-substituted acetophenone derivatives were elucidated based on H^α-F and C^α-F through-space spin-spin couplings (TS-couplings), which occur between two atoms constrained at a distance smaller than the sum of their van der Waals radii. This study revealed that 2'-fluoro-substituted acetophenone derivatives in solutions form exclusively s-trans conformers by analyzing their NMR spectra focused on the TS-couplings. The magnitudes of the coupling constants ⁵J (H^α, F) and ⁴J (C^α, F) correlate linearly with the value of the dielectric constant of the solvents. Furthermore, s-trans conformations of the two derivatives were confirmed by X-ray crystallographic analysis. These conformational preferences were consistent with the DFT calculations. The s-cis conformer, in which fluorine and oxygen atoms lie in a syn-periplanar mode, may be subject to strong repulsion between the two polar atoms and become unstable. The s-trans preference of the 2'-fluoro-substituted acetophenone derivatives may be utilized in drug design.

SUBMITTER: Otake C 

PROVIDER: S-EPMC8154564 | biostudies-literature | 2021 Mar

REPOSITORIES: biostudies-literature