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

• Published in: Canadian journal of chemistry Vol. 74; no. 8; pp. 1437 - 1446
• Main Authors: Buchanan, G.W, Moghimi, A, Ratcliffe, C.I
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.08.1996
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v96-161

Large-amplitude solid phase molecular motion has been detected in the macrocyclic ring of the title crown either via 13 C CPMAS NMR. To study the details of the dynamic processes, two selectively deuterated d 4 derivatives have been prepared and examined via 2 H 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 CD 2 groups. The amplitude of the CD 2 motions apparently decreases the closer the group is to the aromatic ring. The influence of KNCS complexation on the 13 C CPMAS spectrum and on 13 C spin lattice relaxation times in solution has been explored. Key words: macrocyclic ethers, solid phase dynamics.