The symmetric part of the31P NMR chemical shielding tensor was determined in a single crystal of 2hyphen;aminoethylphosphonic acid (AEP). The principal values, relative to 85percnt; H3PO4, are sgr;11=87.1, sgr;22=15.6, and sgr;33=minus;47.5 ppm. Four orientations of the chemical shielding tensor on the molecule are possible, but only one of them shows correlation with the bond directions. The two most shielded components of the tensor lie almost in the plane containing the two P=O bonds, with sgr;22approximately bisecting the Ondash;Pndash;O angle and sgr;33roughly along the Ondash;O connecting vector, leaving the phosphorus relatively deshielded in the perpendicular sgr;11direction. The results can be correlated with the electron density distribution around the phosphorus atom, as determined by the bonding pattern of the phosphonate. A comparison is made with31P NMR chemical shielding tensors in analogous phosphorushyphen;containing compounds.
展开▼
