Ermittlung der anisotropen brown'schen rotation monosubstituierter diphenyle in flüssiger phase durch 13CTfl-messungen

Measurements of spin lattice ¹³C-relaxation times of protonated carbon atoms in monosubstituted diphenyls are described. It was possible to obtain the various T₁-times as a function of the anisotropic Brownian rotation by application of Woessner's theory. Two diffusion rates for the “overall” motion were derived from the T₁-values. It was ascertained that the anisotropy of rotation is fundamentally greater than the theoretical value, owing to the mass moments of inertia. This is caused by the very high “frictional effect” on the C_xy-rotation. The intramolecular rotation of the phenyl group was determined by two models of motion. The barrier of rotation was obtained from quadrupole T₁-data. These barriers are nearly the same as the values obtained using quantum-mechanics. The dependence of the barrier of rotation upon Hammett's σ_m-parameter is evident.