title: Theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis-, and trans-1,2-difluoroethylenes.
abstract: A theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis- and trans-1,2-difluoroethylenes is reported. The results obtained using density functional theory (DFT) combined with large basis sets and gauge-independent atomic orbital calculations were critically compared with experiment and conventional, higher level correlated electronic structure methods. Accurate structural, vibrational, and NMR parameters of difluoroethylenes were obtained using several density functionals combined with dedicated basis sets. B3LYP/6-311++G(3df,2pd) optimized structures of difluoroethylenes closely reproduced experimental geometries and earlier reported benchmark coupled cluster results, while BLYP/6-311++G(3df,2pd) produced accurate harmonic vibrational frequencies. The most accurate vibrations were obtained using B3LYP/6-311++G(3df,2pd) with correction for anharmonicity. Becke half and half (BHandH) density functional predicted more accurate (19)F isotropic shieldings and van Voorhis and Scuseria's τ-dependent gradient-corrected correlation functional yielded better carbon shieldings than B3LYP. A surprisingly good performance of Hartree-Fock (HF) method in predicting nuclear shieldings in these molecules was observed. Inclusion of zero-point vibrational correction markedly improved agreement with experiment for nuclear shieldings calculated by HF, MP2, CCSD, and CCSD(T) methods but worsened the DFT results. The threefold improvement in accuracy when predicting (2)J(FF) in 1,1-difluoroethylene for BHandH density functional compared to B3LYP was observed (the deviations from experiment were -46 vs. -115 Hz).
authors.affiliation: Department of Physics, 4513 Manhattan College Parkway Riverdale, New York 10471, USA.
authors.forename: Farhod
authors.initials: F
authors.lastname: Nozirov
authors.affiliation: Department of Physics, 4513 Manhattan College Parkway Riverdale, New York 10471, USAFaculty of Chemistry, Opole University, 48, Oleska Street, 45-052 Opole, Poland.
authors.forename: Teobald
authors.initials: T
authors.lastname: Kupka
authors.affiliation: Faculty of Chemistry, Opole University, 48, Oleska Street, 45-052 Opole, Poland.
authors.forename: Michał
authors.initials: M
authors.lastname: Stachów