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Computational NMR coupling constants: shifting and scaling factors for evaluating 1JCH
J San Fabián1, J M García de la Vega, R Suardíaz
1Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
Magnetic Resonance in Chemistry : MRC
|October 15, 2013
Summary
Optimized factors significantly improve calculations of one-bond carbon-hydrogen spin-spin coupling constants ((1)JCH). Applying shifting constants reduces errors, making various computational models more accurate for organic molecules.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Spectroscopy
Background:
- Accurate calculation of one-bond carbon-hydrogen spin-spin coupling constants ((1)JCH) is crucial in molecular characterization.
- Density Functional Theory (DFT) is a common method, but its accuracy for (1)JCH can be improved.
Purpose of the Study:
- To optimize shifting and/or scaling factors for DFT calculations of (1)JCH.
- To assess the performance of various DFT functionals and basis sets for predicting (1)JCH.
Main Methods:
- Evaluated 35 functional/basis set combinations for 68 organic molecules.
- Compared computed (1)JCH values with experimental data.
- Investigated the impact of shifting constants and rovibrational contributions.
Main Results:
- Optimized shifting constants substantially improved the accuracy of calculated (1)JCH.
- Root-mean-square deviations decreased from 4.7-16.4 Hz to 4-6.5 Hz with shifting constants.
- Specific functional/basis set combinations (e.g., PBE/HIII-su3) showed good agreement after accounting for rovibrational effects.
Conclusions:
- Shifting constants are effective for enhancing DFT accuracy in (1)JCH calculations.
- The choice of functional and basis set impacts predictive power.
- DFT methods, when optimized, provide reliable (1)JCH values for organic systems.
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