Structural studies of cyclohexane IV

We report an extensive neutron powder diffraction study of the high-pressure phase IV of cyclohexaned 12 . Using constrained Rietveld refinement we deduce approximate atomic positions for this phase which are found to be in close accord with the predictions of energy-minimization calculations. The likely relationship between the unit cell of phase IV and that of the ambient-pressure phase II is also presented. We further demonstrate, by means of an X-ray powder diffraction study of cyclohexane-h 12 , that phase IV can be produced in a metastable state at ambient pressure by rapid quenching to 77 K from the liquid. This finding contradicts a previous report [Burns & Dacol (1984). Solid State Commun. 51, 773-775] claiming that the ambient-pressure metastable phase is an orientational glass