Anisotropic rotational motion and internal rotation in liquid methylbenzenes

摘要: The usual semiquantitative evaluations of temperature-dependent dipolar 13C spin-lattice relaxation times liquid methylbenzenes (toluene, xylenes, tri- and tetramethylbenzenes), which assume isotropic molecular motion, do not allow any reliable statements to be made about the various hindered rotations methyl groups, preferred rotation axes. quantitative evaluation experimental data using a new formalism (complete anisotropic motion with arbitrary position internally rotating groups) gave following: physically meaningless results were obtained in all cases for optimizations one three possible axially symmetrical ellipsoidal motions, most complete motion. A takes into account is—at least methylbenzenes—only promising if present 10 per cent level error can red...