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.