THE HYDROXONIUM PERCHLORATE COMPLEX OF CIS-SYN-CIS-DICYCLOHEXANO 18-CROWN-6 ETHER - CONFORMATIONAL-ANALYSIS IN THE SOLID-STATE AND IN SOLUTION AT LOW-TEMPERATURE AS STUDIED VIA C-13 NMR METHODS

From 100.6-MHz C-13 NMR coalescence temperature measurements, the title complex is shown to undergo a single degenerate ring inversion process with a free energy barrier of 49.4 -/+ 1.6 kJ/mol. This is ca. 5 kJ/mol higher than the barrier in the free crown. The solid state C-13 CPMAS spectrum is indicative of a totally unsymmetrical conformation and the shift trends in the solid are analyzed in terms of local torsional angle variations. Comparisons of experimental vs. calculated (GIAO) C-13 chemical shift ranges for the CH2O carbons in the solid are made and satisfactory agreement with respect to the overall range and magnitude of the C-13 shielding differences is obtained.