Molecular motion in crown ethers. Application of 13C and 2H NMR to the study of 4-carboxybenzo-24-crown-8 ether and its KNCS complex in solution and in the solid phase

Article abstract of DOI:10.1139/v96-161

Large-amplitude solid phase molecular motion has been detected in the macrocyclic ring of the title crown either via ¹³C CPMAS NMR. To study the details of the dynamic processes, two selectively deuterated d₄ derivatives have been prepared and examined via ²H NMR as a function of temperature. A phase change occurring around 277 K has been verified by differential scanning calorimetry (DSC) and a model for the motional processes has been developed involving equivalent two-site flips of the CD₂ groups. The amplitude of the CD₂ motions apparently decreases the closer the group is to the aromatic ring. The influence of KNCS complexation on the ¹³C CPMAS spectrum and on ¹³C spin lattice relaxation times in solution has been explored.