Relaxation-allowed cross-peaks in two-dimensional NMR correlation spectroscopy

An anal. was made of the effects of nonexponential transverse relaxation during the free precession periods of 2-dimensional NMR expts. The presence of cross-correlation between various interactions that cause relaxation, such as chem. shift anisotropy and dipole-dipole interactions, may lead to the creation of spin-ordered states that make coherence transfer processes possible in spite of the absence of scalar, dipolar or quadrupolar splittings. The principal example discussed in the context of 2-dimensional correlation expts. is the occurrence of cross-peaks between 2 spins which are not scalar coupled to one another. The misinterpretation of these novel effects can represent a pitfall to the NMR spectroscopist, while their correct interpretation may provide useful evidence about the spatial arrangement of the nuclei. [on SciFinder (R)]