The Dipole-dipole Relaxation Time and Internal Motions of the Cyclic Oligoethers. Part. III The Activation Energies of Pseudorotation of 1,4,7,10-tetraoxacyclododecane and its Li,+ Ca2+ Mg2+ Complexes

The ¹³C Dipole-dipole relaxation time and the activation energies of internal motion of cyclic ether backbone were obtained for the 1,4,7,10-tetraoxacyclododecane(12. crown. 4) and its cationic complexes. ¹³C dipolar relaxation time,T^DD ₁ of free tetraoxacyclododecane molecule and its Li,⁺ Ca²⁺ and Mg²⁺ complexes were determined at various temperatures in DHO and CH₃OD solutions at 15.0 MHz. The pseudorotation barriers of oxyethylene bridges were investigated throughout the temperature dependence of dipole-dipole relaxation times which verified that the T^DD ₁ values closely depend on the energy requirements of the particular dynamic processes of molecular systems as well as ion-dipole interactions of cation-cyclic ether. Namely, we concluded a simple analogy between the correlation times of the ¹³C spins and the observed T^DD ₁ values in the vicinity of free and complexing systems. On the other hand our experimental results were correlated with the strain energy minimization calculations previously published, which have strongly proved our presented results.