Dynamic Polarization of 31P Nuclei: Some Evidence for Stereospecific Hyperfine Interactions in Liquids

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Abstract
Dynamic nuclear polarization parameters were compared for all combinations of three free radicals and eight representative phosphorus compounds. The chemical nature of the phosphorus compound is shown to be much more significant than that of the radical in determining the degree of scalar coupling. This contrasts sharply with fluorine, where the radical was equally important, and reflects the more complex geometry and bonding associated with phosphorus compounds. The degree of scalar coupling can be correlated with stereospecific interactions between phosphorus substituents and sites of high spin density on the radical, suggesting the formation of virtual transient bonds.