INTRAMOLECULAR MOTIONS IN CRYSTALLINE PHOSPHONIUM SALTS STUDIED BY P-31 AND C-13 CP-MAS NMR-SPECTROSCOPY

Three homologous trimethylphosphonium bromides with benzyl (1), 2-phen ylethyl (2) and 3-phenylpropyl (3) groups were synthesised and their i nternal conformational motions were examined by solid-state NMR techni ques. For compounds 2 and 3 a Combination of dynamic line shape change s and T-1 beta measurements of C-13 and P-31 nuclei allow the activati on parameters for trimethylphosphonium group rotation in the crystalli ne solid to be determined, There is excellent agreement between the th ree independent but complementary NMR methods on the rates of rotation and the activation parameters for the rotation processes. In 1 the ra te of rotation of the trimethylphosphonium group is too rapid to be me asured.