PHASE-TRANSITION IN CYCLOHEXATRIACONTANE AS STUDIED BY VARIABLE-TEMPERATURE C-13 CP MAS NMR-SPECTROSCOPY

Variable-temperature C-13 CP/MAS spectra of cyclohexatriacontane (C36H72) in the solid state over a wide range of temperatures were measured, in order to study the phase transition and conformational change of the molecule with temperature. The signals associated with the constrained gauche conformations clearly appear in the spectra at temperatures below 0-degrees-C. A new peak at about 30.3 ppm is observed in the C-13 CP/MAS spectrum at 0-degrees-C. The relative intensity of this peak increases gradually and the other signals become broad with an increase in temperature. This indicates the existence of the "pseudorotator phase" in which C36H72 is undergoing fast conformational interconversion before the melting transition.