Kinetic Studies of Fast Equilibrium by Means of High-performance Liquid Chromatography. X. Separation of Rotamers of Acetanilides

Abstract
The restricted rotation about the carbonyl–nitrogen bonds of acetanilides has been investigated by means of high-performance liquid chromatography. The separation of two rotamers (E- and Z-forms) of acetanilides has been achieved at low temperatures. The presence of a very small amount of the E-form has been confirmed for 3-, 4-, and non-substituted acetanilides. The ratios of the E- and Z-forms in different solvents have also been determined. By combining the HPLC and NMR results, it has been elucidated that the molecular structure of acetanilide in solution can be described in terms of an equilibrium between a large amount of the nearly planar Z-form and a small amount of the twisted E-form.

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