Improving the Accuracy of Computed 13C NMR Shift Predictions by Specific Environment Error Correction: Fragment Referencing

Andrews, Keith G.; Spivey, Alan C.

Abstract

The accuracy of both Gauge-including atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) 13C NMR spectra prediction by Density Functional Theory (DFT) at the B3LYP/6-31G** level is shown to be usefully enhanced by employing a ‘fragment referencing’ method for predicting chemical shifts without recourse to empirical scaling. Fragment referencing refers to a process of reducing the error in calculating a particular NMR shift by consulting a similar molecule for which the error in the calculation is easily deduced. The absolute accuracy of the chemical shifts predicted when employing fragment referencing relative to conventional techniques (e.g., using TMS or MeOH/benzene dual referencing) is demonstrated to be improved significantly for a range of substrates, which illustrates the superiority of the technique particularly for systems with similar chemical shifts arising from different chemical environments. The technique is particularly suited to molecules of relatively low molecular weight containing ‘non-standard’ magnetic environments, e.g., α to halogen atoms, which are poorly predicted by other methods. The simplicity and speed of the technique mean that it can be employed to resolve routine structural assignment problems that require a degree of accuracy not provided by standard incremental or hierarchically ordered spherical description of environment (HOSE) algorithms. The approach is also demonstrated to be applicable when employing the MP2 method at 6-31G**, cc-pVDZ, aug-cc-pVDZ, and cc-pVTZ levels, although none of these offer advantage in terms of accuracy of prediction over the B3LYP/6-31G** DFT method.

Citation

Andrews, K. G., & Spivey, A. C. (2013). Improving the Accuracy of Computed 13C NMR Shift Predictions by Specific Environment Error Correction: Fragment Referencing. Journal of Organic Chemistry, 78(22), 11302-11317. https://doi.org/10.1021/jo401833b

• Journal Article Type: Article
• Online Publication Date: Nov 6, 2013
• Publication Date: Nov 15, 2013
• Deposit Date: May 14, 2024
• Journal: The Journal of Organic Chemistry
• Print ISSN: 0022-3263
• Electronic ISSN: 1520-6904
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 78
• Issue: 22
• Pages: 11302-11317
• DOI: https://doi.org/10.1021/jo401833b
• Public URL: https://durham-repository.worktribe.com/output/2438831