CROSS-CORRELATION EFFECTS IN 2-SPIN XH SYSTEMS IN (C6H5)(3)XH AND CHEMICAL-SHIFT ANISOTROPY FOR H-1 AND X=C-13, SI-29, AND SN-119

Longitudinal nuclear spin relaxation studies in heteronuclear two-spin XH systems in triphenyl derivatives, (C6H5)(3)XH, with X = C-13, Si-2 9, and Sn-119 are reported. Spin-lattice relaxation times and nuclear Overhauser enhancement factors for the X nuclei have been measured usi ng conventional, one-dimensional NMR experiments characterizing the re orientational dynamics of the three systems in solution. Two-dimension al exchange spectroscopy has been applied to the same systems to measu re the interference effects between the dipole-dipole and chemical shi ft anisotropy (the cross-correlation rates) for both the X nuclei and the protons bonded to them. The results of the one- and two-dimensiona l experiments are compared and combined in order to estimate the aniso tropies of the shielding tensors for the X nuclei and protons. For X = C-13 and Si-29, the shielding anisotropies from the liquid-state rela xation experiments are compared with the measurements on the solid pow ders.