A DEUTERIUM NMR-STUDY OF GUEST MOLECULAR-DYNAMICS OF ACETONE IN 2 ORGANIC INCLUSION-COMPOUNDS

Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice re laxation times (T-1) are used to investigate the dynamics of the guest molecule, acetone, in tris(5-acetyl-3-thienyl)methane (TATM) and cycl otriveratrylene (CTV) inclusion compounds. C-13 CPMAS powder NMR spect ra were obtained for each clathrate, to verify inclusion. In acetone: TATM, the guest molecule is undergoing twofold reorientation about the CO bond, exchanging the two methyl groups. An activation energy of 20 .8 (+/- 1.4) kJ/mol, for the two-site jump motion, was found, independ ently, from deuterium NMR spectra and T-1 measurements. Acetone in CTV performs the same type of motion as acetone in TATM. Activation energ ies of 25.0 (+/- 3.2) kJ/mol and 24.1 (+/- 0.5) kJ/mol were determined using the same two techniques. In both inclusion compounds, the rate of methyl rotation within the acetone molecule is greater than 10(8) H z even at the lowest temperature measured (84 K). Analytical expressio ns for the spin-lattice relaxation time (T-1), for a twofold jump, wer e derived. Calculated values of the effective quadrupolar coupling con stant and T-1min for the guests agree very well with the experimental data. The 84 K spectrum of acetone:TATM unexpectedly shows some asymme try, the origin of which is discussed. Finally, these two clathrates a re compared to the recently examined acetone:tri-ortho-thymotide inclu sion compound.