Mag. Res. Chem. 46, 1003-1006 (2008)

DOI: 10.1002/mrc.2304

Resolving an apparent discrepancy between theory and experiment: spin-spin coupling constants for FCCF

Ab initio equation of motion coupled cluster singles and doubles (EOM–CCSD) and second-order polarization propagator approximation (SOPPA) calculations have been performed to evaluate spin–spin coupling constants for FCCF (difluoroethyne). The computed EOM-CCSD value of 3J(F[BOND]F) obtained at the experimental geometry of this molecule supports the previously reported experimental value of 2.1 Hz, thereby resolving an apparent discrepancy between theory and experiment. This coupling constant exhibits a strong dependence on the C[BOND]C and C[BOND]F distances, and its small positive value results from a sensitive balance of paramagnetic spin-orbit (PSO) and spin-dipole (SD) terms. The three other unique FCCF coupling constants 1J(C[BOND]C), 1J(C[BOND]F), and 2J(C[BOND]F) have also been reported and compared with experimental data. While 1J(C[BOND]F) is in agreement with experiment, the computed value of 2J(C[BOND]F) is larger than our estimate of the experimental coupling constant.