Mesomorphic State of Cyclotetradecane

Article abstract of DOI:10.1021/ja00259a031

Cyclotetradecane shows a thermal transition 7 K below the melting point.The high-temperature crystal phase is characterized by high molecular mobility and easy deformation.Thermal analysis, MAS 13C NMR with high-power proton decoupling, X-ray diffraction, and birefringence experiments have been performed and are discussed with respect to the onset of molecular motion and molecular disorder.The NMR experiments clearly show the onset of a conformational interconversion process well below the transition, while the positional, orientational, and conformational order are largly preserved.The same applies to some extent even within the high-temperature crystal phase.It is thus shown that molecular dynamics must be strictly differentiated from molecular and crystal disorder.Disordering of molecules with low symmetry such as cyclotetradecane is shown to result in rather large transition entropies, even when the molecular motins are jumplike and involve only minor disorder in the crystal.The concepts of liquid crystal, plastic crystal, and condis-crystal are discussed with regard to the classification of the mesomorphic character of the high-temperature crystal phase of cyclotetradecane.It is classified as a molecule that shows a mesophase with partial orientational disorder and high conformational mobility.