Longitudinal NMR relaxation studies of molecular structure and dynamics in PHO−23

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Abstract
The NMR longitudinal relaxation of a coupled two spin system has been investigated for the case where two relaxation mechanisms, namely, dipole–dipole and chemical shift anisotropy, are present. A method for determining correlation times, as well as bond distances and chemical shift anisotropies for molecules in solution is presented. This method requires that a set of experiments, including inversion of one nucleus and observation of the other as well as ordinary inversion–recovery experiments, be performed at a single temperature. For PHO2−3 in solution, the P–H internuclear distance as found to be 1.48 Å, the phosphorous chemical shift anisotropy was 123 ppm and the proton chemical shift anisotropy was −5.8 ppm.