31P NMR chemical shielding tensors of diethyl [5,6-dichloro-1,3-benzodioxol-(2)] phosphonate

Abstract

The 31P NMR chemical-shift tensors of diethyl [5,6-dicholoro-1,3-benzodioxol-(2)] phosphonate were measured in a single crystal. A crystal symmetry of P1 in contrast to P 1 − claimed by earlier X-ray studies was found. The principal values of the 31P NMR shielding tensors δ(A) and δ(B), or relative to 85% H 3PO 4, are (A) δ 11 = −90.6, δ 22 = −37.8 and δ 33 = 106.2 ppm, and (B) δ 11 = −89.6, δ 22 = 38.3 and δ 33 = 104.3 ppm. The principal directions corresponding to δ 22 and δ 33 lie in the pseudo-mirror planes spanned by the OPC7 molecular fragments. The most shielded directions are almost parallel to the PO bonds. The centrosymmetry of the two molecules in the unit cells is violated by a small rotation about the α axis of one molecule with respect to the other.