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Regression formulae for ab initio and density functional calculated chemical shifts
N J R van Eikema Hommes1, Timothy Clark
1Computer-Chemie-Centrum, Universität Erlangen-Nürnberg, Nägelsbachstrasse 25, 91052, Erlangen, Germany.
Journal of Molecular Modeling
|March 25, 2005
Summary
This study provides linear regression formulas to convert calculated magnetic shielding constants into chemical shifts for 1H and 13C. These accurate conversion methods are useful for computational chemistry, even with standard calculations.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Spectroscopy
Background:
- Accurate prediction of nuclear magnetic resonance (NMR) chemical shifts is crucial in chemistry.
- Ab initio and density functional theory (DFT) methods are widely used for calculating molecular properties.
- Converting calculated magnetic shielding constants to chemical shifts can be challenging.
Purpose of the Study:
- To develop reliable linear regression formulae for converting 1H and 13C magnetic shielding constants to chemical shifts.
- To assess the accuracy of these formulae across various computational levels.
- To compare the performance of high-level versus economical computational methods.
Main Methods:
- Calculated 1H and 13C magnetic shielding constants using common ab initio and DFT methods.
- Developed linear regression models to correlate shielding constants with experimental chemical shifts relative to tetramethylsilane (TMS).
- Evaluated the accuracy of the developed formulae on a training set.
Main Results:
- Linear regression formulae were established for converting magnetic shielding constants to chemical shifts.
- Achieved accuracies of approximately +/-2.2 ppm for 13C and +/-0.15 ppm for 1H.
- Found that higher-level calculations do not consistently yield superior results compared to standard, economical methods.
Conclusions:
- The developed linear regression formulae provide accurate conversions of calculated shielding constants to NMR chemical shifts.
- Economical computational methods can be sufficient for obtaining reliable chemical shift predictions.
- These findings offer a practical approach for NMR chemical shift prediction in computational studies.