1H/13C chemical shift calculations for biaryls: DFT approaches to geometry optimization.

Thien T Nguyen

doi:10.1098/rsos.210954

Abstract

Twelve common density functional methods and seven basis sets for geometry optimization were evaluated on the accuracy of 1H/13C NMR chemical shift calculations for biaryls. For these functionals, 1H shifts calculations for gas phase optimized geometries were significantly less accurate than those for in-solution optimized structures, while 13C results were not strongly influenced by geometry optimization methods and solvent effects. B3LYP, B3PW91, mPW1PW91 and ωB97XD were the best-performing functionals with lowest errors; among seven basis sets, DGDZVP2 and 6-31G(d,p) outperformed the others. The combination of these functionals and basis sets resulted in high accuracy with CMAEmin = 0.0327 ppm (0.76%) and 0.888 ppm (0.58%) for 1H and 13C, respectively. The selected functionals and basis set were validated when consistently producing optimized structures with high accuracy results for 1H and 13C chemical shift calculations of two other biaryls. This study highly recommends the IEFPCM/B3LYP, B3PW91, mPW1PW91 or ωB97XD/DGDZVP2 or 6-31G(d,p) level of theory for the geometry optimization step, especially the solvent incorporation, which would lead to high accuracy 1H/13C calculation. This work would assist in the fully structural assignments of biaryls and provide insights into in-solution biaryl conformations.

Highlights

Biaryls are prominent substructures found in important, chiral ligands and organocatalysts, which are useful for asymmetric transformations [1,2]
Optimized geometries of biaryl 1 in gas phase and in DMSO using 12 functionals coupled with 6-31G(d,p) basis set were tested on compound 1, which was previously prepared by a two-stepped synthesis from ferulic acid [10]
In-solution structures were about 19 kcal/mol more stable than gas phase ones. These structures were subjected to the 1H and 13C chemical shift calculations and the results are shown in table 2 and figure 2

Summary

Introduction

Biaryls (figure 1) are prominent substructures found in important, chiral ligands and organocatalysts, which are useful for asymmetric transformations [1,2]. They are present in biologically active natural products and biopolymer lignins [3,4]. Biaryls are used for sequencing lignin oligomers [5], oxidative C–C cleavage [6] and pyrolysis behaviour studies [7] and are found to be anti-oxidant and anti-inflammatory agents [8].

Methods

Results

Conclusion