The proton magnetic resonance spectrum of β-propiolactone in two thermotropic nematic solvents

The molecule β-propiolactone has been studied in two thermotropic nematic solvents at 30·5°C. The proton magnetic resonance spectrum shows that the four protons are arranged in a plane with C 2v rather than D 2h symmetry. The interproton distance ratios are in reasonable agreement with the structure previously reported from a study of the rotational spectrum. These ratios are the same within experimental error in both thermotropic solvents reported here. Differences in line width and spectral quality are noted between the two solvents and this suggests that studies in more than one solvent are desirable to obtain the best analysis. The N.M.R. method is especially sensitive to extremely small changes in geometry reflected by the symmetry change D 2h to C 2v .