Fig. 5. Comparison of the experimental vs. DFT-calculated RDC (red) and RCSA (blue) values for caulamidine A (1), the CASE-generated alternative structure 3, and configurational isomers 4 and 5. The Q-value is a quantitative similarity measurement for the DFT-calculated RDC and RCSA values for the structure compared to the experimentally measured data. RDC values define the orientation of the C–H bond vectors for protonated carbons, whereas RCSAs describe the chemical shift tensors for all carbons in the molecule's skeleton.17 For proton-deficient molecules, RCSA data can provide a better assessment of global structural correctness than sparsely available RDCs.
