A NOVEL SUBSTITUENT EFFECT ON 31P NMR CHEMICAL SHIFTS IN THE ARYL DIPHENYLPHOSPHINATE SERIES

The 31 P NMR chemical shifts of a series of meta- and para-substituted phenyl diphenylphosphinates, Ph 2 P(O)OC 6 H 4 -X. have been determined. The δ 31 P values exhibit an increasing downfield trend as the electron-withdrawing properties of the substituent X become greater and a reasonable correlation between δ 31 P and Hammett-Taft substituent constants is obtained. This trend is opposite to that exhibited in several families of compounds of the type ArP(O)Y 2 , where δ 31 P values show an increasing upfield trend as the electron-withdrawing ability of the substituent in Ar is increased. The results are explained by proposing varying degrees of d-orbital occupancy in the phosphorus-oxygen bonds (P-OAr and P˭O) in the series of compounds as a factor influencing 31 P chemical shifts.