DEUTERIUM NMR-STUDY OF THE ADAMANTANE THIOUREA AND BICYCLO[2.2.2]OCTANE THIOUREA INCLUSION-COMPOUNDS

Motionally narrowed isotropic H-2 NMR line shapes are observed for the adamantane-d16-thiourea inclusion compound, 1, at temperatures between 333 and 119 K. The H-2 NMR spin-lattice relaxation times indicate that reorientational motion of the guest is taking place on the picosecond time scale at 300 K. The 2H NMR data suggest that there is only one solid phase for 1 over the temperature range studied and that the effective barrier to overall reorientation of the guest is small, 11.1 +/- 1.1 kJ mol-1. Isotropic H-2 NMR line shapes are also observed for the guest in the bicyclo[2.2.2]octane-d2-thiourea inclusion compound, 2, between 333 and almost-equal-to 183 K. At temperatures less than 183 K a small quadrupolar splitting develops in the H-2 NMR line shape, suggesting that a phase transition has taken place. Below 164 K a second splitting in the line shape is apparent, implying that there are at least two different pest sites. While the magnitude of the first observed quadrupolar splitting remains essentially independent of temperature, the second splitting increases as the temperature is decreased. The H-2 NMR spin-lattice relaxation times of the pest in 2 appear to be continuous over the complete temperature region investigated, 333-123 K. The correlation time for overall reorientations of bicyclo[2.2.2]octane-d2 in 2 is less than 3 X 10(-9) s at temperatures above 123 K, and the E(A) for this motion is 9.4 +/- 0.9 kJ mol-1.