Solid-state NMR studies on the orthorhombic-to-hexagonal phase transition for alpha ,omega -alkanediol crystals

Studies on the orthorhombic and hexagonal phases of alpha ,omega -alkanediols have been performed by solid-state NMR. In the cross-polarization/magic angle spinning 13C NMR spectrum for the orthorhombic phase of 1,23-tricosanediol (HO–(CH2)23–OH), the resonance line assigned to the inner CH2 is observed at 32.9 ppm and two resonance lines appear for the alpha -CH2 and gamma -CH2 carbons at chain ends. These doublets are due to the different chain ends with the all-trans and the gaucheincluded conformations. 13C spin-lattice relaxation time measurements reveal that the chain end including the gauche conformation is less mobile compared to another chain end consisting of the all-trans conformation. It is also found that the monoclinic–hexagonal phase transition behavior for the 1,20-eicosanediol (HO–(CH2)20–OH) crystallized from toluene solution by quenching is almost the same as the case of the 1,20-eicosanediol sample crystallized by slowly cooling from the toluene solution which was previously reported.