COUPLED-SPIN RELAXATION OF AX(2) SPIN SYSTEMS IN THE PRESENCE OF NEIGHBORING SPINS

In order to assess the influence of neighboring intramolecular spins o n the use of coupled-spin relaxation as a probe of chain motion, the s pin relaxation of the central (CH2)-C-13 group in [5-C-13]nonane and i ts deuterated isotopomer, C4D9-(CH2)-C-13-C4D9, is compared. Modeling interactions with neighboring spins as random fields is sufficient to allow reliable evaluation of three of four dipolar spectral densities of the central methylene (J(CH), J(HCH), and J(CHH)) If the Cartesian correlation times tau(xx) and tau(yy), are assumed to be equal (tau(pe rpendicular to)), these three dipolar spectral densities can be transf ormed into three correlation times (tau(perpendicular to) , tau(zz), a nd tau(xy)). These techniques should be useful in applying coupled-spi n-relaxation methods in the absence of rigorously isolated spin system s. (C) 1994 Academic Press,Inc.