Chemical Shifts

Abstract

A perusal of the ³¹P NNR literature involving metal complexes reveals that the discussion, offen, centers around the coupling of phosphorus to another nuclei. This statement does not imply a lack of interest in the ³¹P chemical shift but rather that additional effort has been expended in the direction of coupling constants since these seemed more readily understood. Like most nuclei other than ¹H, the normal ³¹P chemical shift range is large (> 200 ppm) with the screening for a given phosphorus generally thought to be determined by the expressions shown in equation (3.1) [183]:

$${{\sigma }_{t}}={{\sigma }_{P}}+{{\sigma }_{D}}+{{\sigma }_{X}}$$

(3.1)

in which the total screening, σ_t, consists primarily of contributions from the paramagnetic term, σ_P (which has nothing to do with paramagnetism) and the diamagnetic term, σ_D. Included in the contribution σ_X, are electric field effects, anisotropic effects and the changes in δ³¹P resulting from ring currents, solvents, temperature etc.