A proton magnetic resonance study of the influence of the solvent on the rotation about the carbamate amide bond in N‐(benzyloxycarbonyl)‐L‐proline t‐butyl ester

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Abstract
The NMR spectrum of N‐(benzyloxycarbonyl)‐L‐proline t‐butyl ester shows two t‐butyl signals of slowly interconverting syn and anti rotamers. The t‐butyl signals have been assigned to the syn and the anti form by using Eu(fod), as a shift reagent. The thermodynamic parameters ΔG≠, ΔH≠ and ΔS≠ for rotation about the amide bond have been determined by the method of Shanan — Atidi and Bar‐Eli and by complete line shape analysis, in four solvents of different polarity. The results are discussed.