DYNAMICS OF 5-MEMBERED RINGS IN THE SOLID-STATE BY NMR-SPECTROSCOPY

The carbon-13 NMR spectra have been investigated in the solid state for a number of fundamental five-membered rings and some analogous six-membered rings. Several of these rings freeze into a plastic phase, whose NMR spectrum retains the symmetry of the liquid-phase spectrum. At the plastic-to-nonplastic transition, these spectra can undergo decoalescence to spectra characteristic of the symmetry and structure within the solid. Motion within the solid also broadens peaks when the motional frequency is comparable to the spin-lock precessional frequency. In the nonplastic phase, cyclopentanol exists in at least two sites, and possibly more, which probably result from hydrogen-bonded aggregation. Cyclohexanol may exist in two such sites. Cyclopentanone exists in two equally populated sites. 1-Methylcyclopentanol and trans-1,2-cyclohexanediol exist either in two equally populated sites or as a single, unsymmetrical form. Cyclohexanone, trans-1,2-cyclohexanediol, and tetrahydrothiophene 1-oxide appear to exist in single forms. Sulfolane exists in two, unequally populated sites.