Two conformations of each of the title molecules have been detected by 100 MHz I3C NMR at 210 K. For the dicyclohexyl systems, the conformations are related via a single ring inversion. In each case the equatorial-axial conformer is 4.7 ? 0.4 kJ/mol less stable than the diequatorially substituted form in CD2CI2 solution. For monosubstituted models, the conformational free energy (-AGO) values of the -0-CH,-CH2-0CH3, -OCH,-CH2-0-CH,-CH,, and -0-CH2-CH2-0-CH-(CH,), groups have been determined to be 5.4.6.1, and 6.1 + 0.2 kJ/mol, respectively. In methanol, the latter equilibria are slightly more biased towards the axially substituted conformers.Key words: substituted ethylene glycols, conformational equilibria.

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The structures of the title systems have been determined by X-ray crystallography. The sodium iodide complex has 2 : 2 stoichiometry and Ci symmetry. Each sodium cation coordinates to four oxygen atoms of one macrocyclic unit and one oxygen of the other 15-membered ring of the dimer. The 400 MHz 'H NMR spectra have been analysed and assignments made on the basis of NOESY and COSY experiments. Solution ' 3C NMR spectra have been assigned using HETCOR methods. Solid-phase 13C NMR spectra are included and the results of sodium complexation on the solid-phase 13C chemical shifts are discussed. [4-2H,] Dibenzo-15-crown-4 has been synthesized and employed as an aid in spectral assignments.Paper 4/058 1 3E

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