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GIAO NMR shift calculation has been applied to the challenging task of reliably assigning stereochemistry with quantifiable confidence when only one set of experimental data are available. We have compared several approaches for assigning a probability to each candidate structure and have tested the ability of these methods to distinguish up to 64 possible diastereoisomers of 117 different molecules, using NMR shifts obtained in rapid and computationally inexpensive single-point calculations on molecular mechanics geometries without time-consuming ab initio geometry optimization. We show that a probability analysis based on the errors in each (13)C or (1)H shift is significantly more successful at making correct assignments with high confidence than are probabilities based on the correlation coefficient and mean absolute error parameters. Our new probability measure, which we have termed DP4, complements the probabilities obtained from our previously developed CP3 parameter, which applies to the case of assigning a pair of diastereoisomers when one has both experimental data sets. We illustrate the application of DP4 to assigning the stereochemistry or structure of 21 natural products that were originally misassigned in the literature or that required extensive synthesis of diastereoisomers to establish their stereochemistry.

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Ermanis, K.; Parkes, K. E. B.; Agback, T.; Goodman, J. M. Org. Biomol. Chem., 2016, 14, 3943-3949Contributed by Steven BacharachReposted from Computational Organic Chemistry with permissionComputational chemistry has had a remarkable impact on the field of...
Computational chemistry has had a remarkable impact on the field of structure determination by NMR spectroscopy. The ability to efficiently compute 13C and 1H chemical shifts allows for comparison of the computed chemical shifts of potential structures against...
Grimblat, N.; Zanardi, M. M.; Sarotti, A. M. J. Org. Chem. 2015, 80, 12526-12534Contributed by Steven BachrachReposted from Computational Organic Chemistry with permissionStructure determination has been greatly facilitated by the use of computed NMR spectra...
Structure determination has been greatly facilitated by the use of computed NMR spectra to compare with experimental spectra. Perhaps the best method for doing this is the DP4 procedure developed by Smith and Goodman.1 (I have a previous post on their paper.)...
Willoughby, P. H.; Jansma, M. J.; Hoye, T. R. Nat. Protocols 2014, 9, 643-660Contributed by Steven Bachrach.Reposted from Computational Organic Chemistry with permissionI have posted on the use of computed NMR chemical shifts and coupling constants to...
I have posted on the use of computed NMR chemical shifts and coupling constants to help aid in structure identification. The second edition of my book Computational Organic Chemistry has a largely all-new chapter on structure identification aided by computed...
What procedure should one employ when trying to determine a chemical structure from an NMR spectrum? I have discussed a number of such examples in the past, most recently the procedure by Goodman for dealing with the situation where one has the experimental...
K. W. Quasdorf, A. D. Huters, M. W. Lodewyk, D. J. Tantillo, N. K. Garg, Journal of the American Chemical Society 2011, 134, 1396 (Paywall)Contributed by Steven Bachrach.Reposted from Computational Organic Chemistry with permissionA quick note...
A quick note here on the use of computed NMR to determine stereochemical structure. The Garg group synthesized two oxidized welwitindolines, compounds 1 and 2.1 The relative stereochemistry at the C3 position (the carbon with the hydroxy group) was unknown.12Low...
Nobilisitine A was isolated by Evidente and coworkers, who proposed the structure 1.1 Banwell and co-workers then synthesized the enantiomer of 1, but its NMR did not correspond to that of reported for Nobilisitine A.; the largest differences are 4.7 ppm for...
Here is a nice example of an interesting synthesis, mechanistic explication using computation (with a bit of an unanswered question), and corroboration of the stereochemistry of the product using computed NMR shifts. Gil and Mischne1 reacted dimedone 1 with...