MOLECULAR-REORIENTATION IN P-FLUORANIL AS STUDIED BY F-19 NMR AND POTENTIAL PROFILE CALCULATIONS

The temperature dependence of the 19F NMR second moments and spin-lattice relaxation times studied between 200 and 440 K reveal the presence of large amplitude molecular reorientation in solid p-fluoranil. The lack of disorder in the crystal structure and the apparent motion invariance of the 19F chemical shielding tensor require the motion to be a 180° flip. The reasonableness of such a motional model was confirmed by potential profile calculations using a Lennard-Jones potential function with parameters adjusted to give approximate agreement with the experimentally derived value for the reorientational activation energy of 8.5±0.4 kcal/mole. © 1979 American Institute of Physics.