The 1H and 13C chemical shifts of 5-5 lignin model dimers: An evaluation of DFT functionals

The calculations of H-1 and C-13 NMR chemical shifts were performed on three 5-5 lignin dimers, prominent substructures in softwood lignins, to compare with experimental data. Initially, 10 DFT functionals (B3LYP, B3PW91, BPV86, CAM-B3LYP, HCTH, HSEH1PBE, mPW1PW91, PBEPBE, TPSSTPSS, and omega B97XD) combined with the gage-including atomic orbital (GIAO) method and basic set 6-31G(d,p) were tested on 3,3'-(6,6'-dihydroxy-5,5'-dimethoxy-[1,1'-biphenyl]-3,3'-diyl)dipropionic acid (1), efficiently synthesized from ferulic acid. HSEH1PBE, mPW1PW91, and omega B97XD were found to be the three best performing functionals with strong correlations (r(2) >= 0.9988) and low errors (CMAEs <= 0.0611 ppm for H-1 and CMAEs <= 1.19 ppm for C-13). These functionals were also well-performed for the H-1 and C-13 shift calculations of dimers 3,3'-dimethoxy-5,5'-dimethyl-[1,1'-biphenyl]-2,2'-diol (2) and 5,5'-diallyl-3,3'-dimethoxy-[1,1'-biphenyl]-2,2'-diol (3). Overall, the omega B97XD functional consistently provided the calculated H-1 and C-13 chemical shifts with a high level of accuracy. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study focused on calculating the H-1 and C-13 NMR chemical shifts of three lignin dimers, revealing that the omega B97XD functional consistently provided accurate results.