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

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Nuclear Magnetic Resonance (NMR) spectroscopy is crucial for biaryl structure elucidation.
• Accurate prediction of NMR chemical shifts aids in spectral assignment and conformational analysis.
• Density functional theory (DFT) is a widely used computational method for predicting molecular properties.

Purpose of the Study:

• To evaluate the accuracy of various density functional methods and basis sets for calculating 1H and 13C NMR chemical shifts in biaryls.
• To determine the influence of geometry optimization methods (gas phase vs. in-solution) on NMR chemical shift prediction accuracy.
• To identify optimal computational strategies for reliable biaryl structure determination using NMR.

Main Methods:

• Systematic evaluation of twelve density functional methods and seven basis sets for geometry optimization.
• Calculation of 1H and 13C NMR chemical shifts for optimized biaryl structures.
• Comparison of calculated shifts with experimental data to assess accuracy.
• Validation of selected methods on additional biaryl systems.

Main Results:

• In-solution optimized geometries yielded significantly more accurate 1H NMR chemical shifts compared to gas-phase optimizations.
• 13C NMR chemical shift calculations were less sensitive to geometry optimization methods and solvent effects.
• B3LYP, B3PW91, mPW1PW91, and ωB97XD functionals, combined with DGDZVP2 or 6-31G(d,p) basis sets, demonstrated the highest accuracy.
• Recommended computational protocols achieved minimal average errors of 0.0327 ppm for 1H and 0.888 ppm for 13C.

Conclusions:

• The study recommends specific DFT functionals (B3LYP, B3PW91, mPW1PW91, ωB97XD) and basis sets (DGDZVP2, 6-31G(d,p)) for accurate 1H/13C NMR chemical shift calculations of biaryls.
• Incorporating solvent effects during geometry optimization is crucial for high-accuracy 1H NMR predictions.
• The findings will aid in the structural assignment of biaryls and provide insights into their in-solution conformations.