Determination of the order of the P=N bond in phosphazo derivatives by a P31 NMR method

Phosphorus-31 Chemical Shifts: Principles and Empirical Observations

“…rPCl 2 + II Supposedly, an increase in the d"-p n bond order was responsible for an increase in the d-orbital occupation on phosphorus and a shift of the 31 P signal to higher field (Grabiak et al, 1980;Tarasevich et al, 1971; see also Ionin, 1968). This common interpretation of the Letcher and Van Wazer theory, however, is much too simplistic because electron withdrawal from phosphorus can lead to shielding or deshielding.…”