Computational NMR Methods in the Stereochemical Analysis of Organic Compounds: Are Proton or Carbon NMR Chemical Shift Data More Discriminating?

• Published in: European journal of organic chemistry 2015-02, Vol.2015 (6), p.1320-1324
• Main Authors: Chini, Maria Giovanna, Riccio, Raffaele, Bifulco, Giuseppe
• Format: Article
• Language: English
• Subjects: Ab initio calculations; Configuration determination; Natural products; NMR; NMR spectroscopy; Nuclear magnetic resonance
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201403569

We have investigated the 1H and 13C NMR chemical shift data of a large set of stereoisomeric organic compounds to determine whether it is possible to identify the nucleus that is more discriminating in stereochemical analyses conducted by quantum mechanical methods. By estimating the intrinsic deviation of the experimental chemical shifts of 219 pairs of diastereoisomers, we have reconsidered the concept of the match ratio as an inequality, namely 1H match ratio > 13C match ratio, mathematically demonstrating that the 1H nucleus is more discriminating than the 13C nucleus for all the investigated cases. Moreover, we have also verified that this inequality is satisfied by the most often used quantum chemical methods, which suggests that 1H chemical shifts are more discriminating than 13C chemical shifts in stereochemical assignments by quantum chemical calculations. The use of 1H NMR DFT calculations is a better choice than the corresponding 13C NMR calculations for assigning the relative configurations of organic compounds.