Measurements of fluorine and phosphorus chemical shift anisotropies

Abstract

The 31P chemical shift anisotropy in the pyrophosphate group has been investigated by measuring the field dependence of the second moment of the N.M.R. absorption lineshape in sodium and potassium pyrophosphates. Assuming axial symmetry the value of σ∥ - σ⊥ was found to be 200 ± 100 p.p.m. A study of the 31P chemical shift in a crystal of sodium pyrophosphate decahydrate gave values of -50, +30, +50 and -10 p.p.m., for the tensor components σ xx , σ yy , σ zz and σ zx , but the crystal symmetry was such that the elements σ xy and σ yz were indeterminate. Investigations of the field dependence of 19F second moments yielded a value of 280 p.p.m. for σ∥ - σ⊥ in both tetrafluorohydroquinone and trifluoroacetanilide, whilst the 19F second moment in trifluoroacetamide showed little if any field dependence.