Methyl group rotation and the low temperature transition in hexamethylbenzene. A neutron diffraction study

摘要: Neutron diffraction studies of single crystals hexamethylbenzene at 298 K and 130 indicate that the molecule in phase II has approximate D3d symmetry. The amplitudes libration methyl group rigid body motions are consistent with earlier data, except barrier to rotation appears be lower by about 0.5 kcal/mol (2100 J/mol).Consideration intra- inter-molecular hydrogen atom contact distances calculated potential energy curves using a 6-exp function suggest intermolecular forces important determining groups substantial changes packing must responsible for lambda-point transition 116 consequent profound change internal which been previously observed.