DYNAMIC NMR-STUDY OF 1,3,5,7-TETRAOXACYCLOOCTANE IN LIQUID AND LIQUID-CRYSTALLINE SOLUTIONS AND IN THE SOLID-STATE

Deuterium, proton, and carbon-13 NMR spectra of 1,3,5,7-tetraoxacycloo ctane (tetroxocane) were recorded in liquid crystalline and isotropic solutions. as well as in the solid state. In solution, tetroxocane exi sts as a mixture of the boat-chair (BC) and crown (Cr) conformers. Pse udorotation and inversion is extremely fast in the BC form, while inve rsion in the crown conformer is relatively slow (on the NMR time scale ). Analysis of the NMR line shape and 2D exchange experiments shows th at the ring inversion in the Cr form occurs via the BC form. Interconv ersion rate constants and equilibrium constants between the two forms over a wide temperature range were determined in several normal and li quid crystalline solvents. In the solid state tetroxocane crystallizes in a (slightly distorted) crown form. Deuterium NMR in a powder sampl e of solid tetroxocane-d(g) exhibits dynamic spectra consistent with m olecular 4-fold jumps about their pseudo-C-4 axes. Quantitative analys is of the dynamic line shape is consistent with a small Ct deformation of the molecule, as found previously by X-ray analysis, and yields th e following kinetic equation for the jump rate, k(J) (s(-1)) = 5.9 x 1 0(16) exp (-15.9/RT), where R is in kcal mol(-1) K-1.