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

We have investigated the H-1 and C-13 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 H-1 match ratio > C-13 match ratio, mathematically demonstrating that the H-1 nucleus is more discriminating than the C-13 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 H-1 chemical shifts are more discriminating than C-13 chemical shifts in stereochemical assignments by quantum chemical calculations.