K. Kuwabara, F. Horii, Y. Ogawa
Jul 12, 2000
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Influential Citations
8
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Journal
Journal of Molecular Structure
Abstract
Abstract The structure and dynamics for the monoclinic and hexagonal crystals of 1,20-eicosanediol (HO–(CH 2 ) 20 –OH) have been investigated mainly by solid-state 13 C and 1 H NMR spectroscopies. In the heating process of DSC curve, a small endothermic peak, which is assigned to the phase transition from one monoclinic phase (M phase) to another monoclinic phase (M′ phase), is observed at 80°C. Moreover, another endothermic peak attributed to the phase transition from the M′ phase to the hexagonal phase (H phase) also appears at 95°C. CP/MAS 13 C NMR and 1 H CRAMPS spectra reveal that two magnetically different structures exist in chain ends associated with hydrogen bonding in the M and M′ phases. The evaluation of the 13 C chemical shift for the CH 2 resonance line by considering the γ- gauche effect indicates that about 3% gauche conformations are included in the inner CH 2 sequences in the H phase. FT-IR measurements also confirm the existence of the kink defects in the H phase. It is also found by T 1C and 1 H CRAMPS measurements that the two-site exchange motion for the hydroxyl groups, because of the jump rotation around the C–O bond, occurs in the H phase. To fulfill the cylindrical symmetry in the H phase, the overall random jump rotation around the chain axis may be induced for more than 80% molecular chains with the almost planar zigzag conformation. However, less than 20% chains will undergo the partial jump rotation by the introduction of kink defects probably as a result of the rather strong fixation of chain ends through intermolecular hydrogen bonding.