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

The carbon-13 NMR spectra have been investigated in the solid state fo r a number of fundamental five-membered rings and some analogous six-m embered rings. Several of these rings freeze into a plastic phase, who se NMR spectrum retains the symmetry of the liquid-phase spectrum. At the plastic-to-nonplastic transition, these spectra can undergo decoal escence to spectra characteristic of the symmetry and structure within the solid. Motion within the solid also broadens peaks when the motio nal frequency is comparable to the spin-lock precessional frequency. I n the nonplastic phase, cyclopentanol exists in at least two sites, an d possibly more, which probably result from hydrogen-bonded aggregatio n. Cyclohexanol may exist in two such sites. Cyclopentanone exists in two equally populated sites. 1-Methylcyclopentanol and trans-1,2-cyclo hexanediol exist either in two equally populated sites or as a single, unsymmetrical form. Cyclohexanone, trans-1,2-cyclohexanediol, and tet rahydrothiophene 1-oxide appear to exist in single forms. Sulfolane ex ists in two, unequally populated sites.