Molecular Characterization of Hexaoctyloxy-Rufigallol in the Solid and Columnar Phases:  A Local Field NMR Study

Separated local field NMR spectroscopy was used to obtain 1H−13C dipolar interactions in the solid and columnar phases of the discotic compound 1,2,3,5,6,7-hexaoctyloxy-rufigallol (RufH8O). The couplings were measured and assigned by a variety of advanced NMR techniques performed under both static and magic-angle spinning conditions. The analysis of the dipolar couplings shows that the three nonequivalent aliphatic chains in RufH8O exhibit vastly different structural and dynamical characteristics. It was also found that one of the α methylene signals exhibits two 1H−13C dipolar splittings at low temperatures in the columnar phase. Similar pairs of doublets have previously been observed in a 2H NMR study of RufH8O−2Hα and were there interpreted in terms of dynamic packing fluctuations along the columns. We will present an alternative explanation and show that these two doublets most likely originate from nonequivalent protons (or deuterons) in the α methylene group and not from density modulations.