The qualitative and quantitative accuracy of DFT methods in computing 1J(C-F), 1J(C-N) and nJ(F-F) spin-spin coupling of fluorobenzene and fluoropyridine molecules

- DFT methods were used to compute the J-coupling of the molecules.
- Right combination of DFT functional with basis set can reproduce high level EOM-CCSD.
- All the methods reproduced the qualitative order of the experimental J-coupling.
- Best quantitative results obtained from PBEPBE combined with aug-cc-pVDZ.

The qualitative and quantitative quality of DFT methods combined with different basis sets in computing the J-coupling of the types 1J(C-F) and nJ(F-F) are investigated for the fluorobenzene and fluoropyridine derivatives. Interestingly, all of the computational methods perfectly reproduced the experimental order for nJ(F-F) but many failed to reproduce the experimental order for 1J(C-F) coupling. The functional PBEPBE gives the best quantitative values that are closer to the experimental spin-spin coupling when combined with the basis sets aug-cc-pVDZ and DGDZVP but is also part of the methods that fail to perfectly reproduce the experimental order for the 1J(C-F) coupling. The basis set DGDZVP combined with all the methods except with PBEPBE perfectly reproduces the 1J(C-F) experimental order. All the methods reproduce either the positive or the negative sign of the experimental spin-spin coupling except for the basis set 6-31+G(d,p) which fails to reproduce the experimental positive value of 3J(F-F) regardless of what type of DFT methods was used. The values of the FC term is far higher than all other Ramsey terms in the one bond 1J(C-F) coupling but in the two, three and four bonds nJ(F-F) the values of PSO and SD are higher.

DFT methods were used to compute the J-coupling of molecules benf, benf2, benf2c, benf2c2, pyrf, pyrfc and pyrfc2, and are presented. Right combination of DFT functional with basis set can reproduce high level EOM-CCSD and experimental J-coupling results. All the methods can reproduce the qualitative order of the experimental J-coupling but not all reproduce the quantitative. The best quantitative results were obtained from PBEPBE combined with the high basis set aug-cc-pVDZ Also, PBEPBE combines with lower basis set DGDZVP to give a highly similar value.355