Density functional study of the one-bond CF coupling constant in α-fluorocarbonyl and α-fluorosulfonyl compounds

1JCF coupling constants of α-fluorocarbonyl and α-fluorosulfonyl model compounds are analyzed at the BHandH/EPR-III level of density functional theory. For fluoroethanal, 1JCF follows the electrostatic-based behavior exhibited by 1,2-difluoroethane, whereas for (fluoromethyl)sulfone, hyperconjugation is indicated to be important as well. The variation of 1JCF during rotation about the CS bond parallels that of the nF → σ*CS donor–acceptor interaction, which is a result of the better electron acceptor ability of the σ*CS(O2) orbital when compared to the corresponding σ*CC(O) orbital of α-fluorocarbonyl compounds. Because the rotational profile of 1JCF is non-monotonic in (fluoromethyl)sulfone, this coupling constant is indicated to be of limited diagnostic value to probe the conformations of α-fluorosulfones.

DFT calculations were used to study the angular dependence of 1JCF in α-fluorocarbonyl and α-fluorosulfonyl compounds; while 1JCF in the former is dependent on dipolar interaction, hyperconjugation also plays an important role for the latter.Figure optionsDownload as PowerPoint slideHighlights
► DFT calculations were used to study the angular dependence of 1JCF in model compounds.
► 1JCF in α-fluorocarbonyl compounds is described by dipolar interactions.
► 1JCF is also dependent on hyperconjugation in α-fluorosulfonyl models.