Configurational assignment of β‐phenylaspartic acids in solution by 1 H and 13 C nuclear magnetic resonance

Vicinal 3 J (HH) and 3 J ( 13 CH) coupling constants are reported for the two diastereoisomers of β‐phenylaspartic acid at various pH values. A comparison between these coupling constants and those expected from the possible conformations of these molecules allows configurational assignments to be made. In strong acidic medium we observed intermediate values for 3 J (HH) for both isomers, for one isomer two intermediate values for 3 J (Co‐α, H‐β) and 3 J (Co‐β, H‐α), and for the other isomer a very small value for 3 J (CO‐α, H‐β) and an intermediate value for 3 J (Co‐β, H‐α). The discussion shows that the former has the RR/SS configuration and the latter the RS/SR configuration.