Nuclear Magnetic Resonance Studies of Enantiomeric Internal Rotational Isomers of 1- and 3-Arylhydantoins in Achiral and Chiral Solvents

Abstract

1H and 13C n.m.r. spectra have been determined for a number of 1- and 3-arylhydantoins in achiral and chiral solvents. These compounds, which have enantiomeric rotational isomers, show restricted internal rotation about the aryl C—N bond at normal probe temperatures. Chemical shifts between corresponding protons on the pairs of rotamers, induced by diastereomeric solute–solvent interactions in the chiral solvent, are strongly dependent on the location of the protons in the solute molecules. In conjunction with 1H and 13C chemical shifts, these data provide information on the geometry of the solvated species. No splitting of signals resulting from the presence of diastereomeric solvates was observable in the 13C spectra. Activation parameters for hindered internal rotation, determined by complete p.m.r. line shape analysis using signals of the diastereotopic methyl groups in the 5-position, show some solvent dependence.