The 13C Dipole-Dipole Relaxation and Pseudorotation of Some Macrocyclic Ethers and a Polyoxalactone

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Abstract
The 13C dipole-dipole relaxation times of tetraoxa-, pentaoxa-, hexaoxa-cyclooctadecane, and dioxohexaoxacyclooctadecane were obtained in acetone-d6 by the aid of the inversion recovery method at 15.0 MHz. The dependence of dipolar relaxation time on the molecular size and the conformational aspects of cyclopolyoxa molecules, n, are discussed from the point of view of the cation-binding properties of such compounds. It is concluded that the T1DD values reflect the rate of pseudorotation and therefore the flexible nature of the ring which causes the preference of the cation binding; accordingly, the rigidity determines the degree of stability of ion-molecule complexes.