15N NMR spectroscopy 24—chemical shifts and coupling constants of α-amino acid N-carboxyanhydrides and related heterocycles†

The chemical shifts of amino acid N-carboxyanhydrides (NCAs) and cyclic or linear urethanes are less sensitive to solvent effects than those of amides and lactams. The values of the one-bond 15N1H coupling constants depend on the solvent and are 5-8 Hz larger than those of ureas and amides. The 15N13C coupling constant of the NCO group is also unusually high, while that of the N—CH group lies within the range known for N-acylated aliphatic amines. The one-bond 15N13C coupling constant was found to be insensitive to conformational changes.

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