Molecular reorientation in crystalline thiophene and furan

Molecular reorientation processes in crystalline thiophene and furan have been studied using pulse nmr techniques, over a range of temperature. The results obtained have been evaluated in the context of literature data on the heat capacities and crystal structures of these systems; this evaluation has been facilitated by the use of potential energy calculations for a molecule in the crystal lattice, based upon the empirical atom–atom approximation for the intermolecular interactions. In the case of furan, all available data can be reconciled in a self-consistent picture of the dynamic structure of the crystal. In the case of thiophene, however, various inconsistencies suggest that the published crystal structure determination should be repeated, and that further work on the pulse nmr at lower temperatures is necessary.