High field solid state 13C NMR spectroscopy of cucurbituril materials

Solid state C-13 NMR spectra of several cucurbituril materials, CB[n] where n = 5, 6, 7 and 8, have been analysed in detail. Where crystal structures are known the complex splitting patterns for the C=O, CH and CH2 resonances can be directly related to the different site symmetries imposed on the CB molecule by the crystal. Conversely, where the structure is not known the NMR splitting patterns can be used to suggest possible symmetries for the CB, and these could conceivably aid in solving crystal structures. The fact that each structure produces a uniquely different C-13 NMR splitting pattern makes it a useful fingerprinting tool which can be used to detect new phases.