On the Unexpected Accuracy of the M06L Functional in the Calculation of ¹J_FC Spin–Spin Coupling Constants

Abstract

One-bond spin−spin coupling constants (SSCCs) between F and C are computed with density functional theory (DFT). Surprisingly, M06L stands out for its striking accuracy, outperforming any other investigated functional, including PBE0, otherwise considered one of the most reliable for couplings involving F. Although the computation of nuclear magnetic resonance (NMR) parameters involving F is known to be a challenging task, even with a rather small basis set as pcJ-1, M06L provides results with a MAD = 11.7 Hz, whereas the average deviation gets as much as 5 times larger for PBE0 (MAD = 60.0 Hz). In the context of SSCCs on the order of 300 Hz, this is particularly remarkable. We find that the accuracy of M06L/pcJ-1 in predicting 1 J FC constants does not stem from a well-suited exchange or correlation part of the functional. Instead, it is believed to arise from a fortuitous cancellation of errors, as revealed by investigating the convergence of the basis set. Our findings also indicate that 1 J FC constants are highly dependent on the amount of exact exchange included in the expression of the functional, with large fractions being critically important to achieving satisfactory results. Studying the effects of the geometry on 1 J FC , we find that optimizing the geometry at the level of theory used to calculate SSCCs generally improves the quality of the results, although the combination of a M06-2X/aug-cc-pVTZ geometry with M06L/ pcJ-1 1 J FC constants best reproduces the experimental data for organofluorine compounds (with the exception of fluoroalkenes).

Four-Component Relativistic Calculations of NMR Shielding Constants of the Transition Metal Complexes—Part 2: Nitrogen-Coordinated Complexes of Cobalt

“…As a result, we carried out geometry optimizations of all nitrogen-coordinated complexes of cobalt using this functional. This was done in line with the recent findings by Giovanetti et al [ 92 ], who studied the effects of the geometry on fluorine spin–spin coupling constants and reached the conclusion that geometry optimization at the same level of theory as that used for the calculation of spin–spin coupling constants generally improves the quality of the final results.…”

Unexpected triaxial preferences in some all-syn 1,3,5-trifluorocyclohexanes

“…The vicinal coupling constants are significantly smaller and measured at 3 J HF =11.5 Hz and 3 J HF = 4.5 Hz only, indicative of predominant gauche relationships in 5 eq . 9,10 It is interesting also to observe the change in the 1 J CF coupling constants in the 13 C-NMR spectra of 5 in solvents of varying polarity. The axial and equatorial conformers are not resolved due to rapid ring interconversion, thus the 1 J CF coupling constant is an average of the triaxial 5 and tri-equatorial 5 populations.…”

Computational 199Hg NMR

“…[70,71,291,292] Examination of the performance of various XC functionals implied for the calculations of NMR chemical shifts and spin–spin coupling constants can be found in a number of related publications. [ 125–132 ]…”

“…[70,71,291,292] Examination of the performance of various XC functionals implied for the calculations of NMR chemical shifts and spin-spin coupling constants can be found in a number of related publications. [125][126][127][128][129][130][131][132] Incorporating relativistic effects into the DFT theory applied for the calculation of NMR properties of compounds containing heavy elements (those like mercury) has become a top priority at present. In this sense, the DFT method is likely to be the best candidate for the extension to the relativistic domain given that DFT provides a reliable description of the electron correlation effects in the calculations of NMR parameters with a very small computational computational cost similar to that of the Hartee-Fock method.…”