TY - JOUR

T1 - On the unexpected accuracy of the M06L functional in the calculation of 1JFC spin-spin coupling constants

AU - de Giovanetti, Marinella

AU - Bitencourt, Luis Felipe Ferraz

AU - Cormanich, Rodrigo

AU - Sauer, Stephan P. A.

PY - 2021/12/14

Y1 - 2021/12/14

N2 - 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. Despite 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 five times larger for PBE0 (MAD=60.0 Hz). In the context of SSCCs in the order of three hundreds Hertz, this is particularly remarkable. We find that the accuracy of M06L/pcJ-1 in predicting 1JFC 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 1JFC constants are highly dependent on the amount of exact exchange included in the expression of the functional, with large fractions being critically important to achieve satisfactory results. Studying the effects of the geometry on 1JFC, 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 1JFC constants best reproduces the experimental data for organofluorine compounds (with the exception of fluoroalkenes).

AB - 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. Despite 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 five times larger for PBE0 (MAD=60.0 Hz). In the context of SSCCs in the order of three hundreds Hertz, this is particularly remarkable. We find that the accuracy of M06L/pcJ-1 in predicting 1JFC 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 1JFC constants are highly dependent on the amount of exact exchange included in the expression of the functional, with large fractions being critically important to achieve satisfactory results. Studying the effects of the geometry on 1JFC, 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 1JFC constants best reproduces the experimental data for organofluorine compounds (with the exception of fluoroalkenes).

KW - Faculty of Science

KW - NMR

KW - Spin-spin coupling constant

KW - density functional theory (DFT)

KW - fluorine chemistry

U2 - 10.1021/acs.jctc.1c00287

DO - 10.1021/acs.jctc.1c00287

M3 - Journal article

C2 - 34751577

VL - 17

SP - 7712

EP - 7723

JO - Journal of Chemical Theory and Computation

JF - Journal of Chemical Theory and Computation

SN - 1549-9618

IS - 12

ER -