The digraphs below confirm the assignments to the enantiomer 3 ( 4), (1 S,2 R,4 S)-2-bromo-2-methylbicyclooctane. Now that you are versed in the method, the priorities around non-duplicate C 4 are C 3>C 8>C 5 because C 3-chain>SS>RS>H. Locate these atoms in structure 2 and convince yourself that C 1 does indeed have the R-configuration! Since RR/SS>RS/SR, the order of carbon atoms attached to non-duplicate C 1 is C 2>C 6>C 7. Now the left hand chain is designated as RS and the right hand chain as SS. In the right hand chain C 4 has the S-configuration because C 3>C 5>C 8. Locate these atoms in structure 2 and convince yourself. It has the R-configuration because C 3>C 8>C 5. In these chains C 2 has been predetermined as having the S-configuration. The two horizontal chains are mirror images and they must be assigned to the second and third priorities. The vertical chain has the top priority while the hydrogen (not shown) at C 1 has the lowest priority. In the "Digraph of C 1" one starts at the non-duplicate atom C 1 and traces the six possible paths back to duplicate atoms C (1) that are each attached to three phantom atoms of atomic number zero. However, NUS spectra must be acquired in NUS mode. Linear Prediction (optional) NUS is superior to Linear Prediction and is now recommended. Under Processing, phase correction, select automatic along F2 and then automatic along F1. To determine the configurations of the bridgehead carbons, C 1 and C 4, a digraph is the method of choice. NOTE to MestreNova users: Automatic phasing usually works. Structure 2 is structure 1 from a different perspective to which we will refer during the ensuing discussion. The shortcoming lay in not applying, in a heirarchical sense, CIP rule 4b (RR/SS>RS/SR) over rule 5 (R>S).įocusing on bromide 1, the configuration of C 2 is "S" with Br>C 1>C 3>C 9. During the middle of the night I realized that the method was faulty because the solution would not accommodate the (1 S,2 R,4 S) enantiomer 3 but would rather predict (1 R,2 R,4 R) which clearly is a non-existent diastereomer. Several days ago I offered a solution to the R/S assignment of the bridgehead carbons of (1 R,2 S,4 R)-2-bromo-2-methylbicyclooctane 1.