Phosphonitrilic derivatives. Part XIV. Fragmentation patterns of the phosphonitrilic fluorides

Abstract

Like the phosphonitrilic chlorides (NPCl₂)_n, the phosphonitrilic fluorides (NPF₂)_n(n= 3–16) break down in the mass spectrometer into a mixture of cyclic and linear species. The parent ions, and more generally the parent series P_nN_nF_x⁺, are always important products, and for (NPF₂)₅ this series forms over 70% of the total fragments. The larger fluorides tend to break down, possibly through transannular interaction, into cyclic fragments, when these are otherwise known to be stable; thus, fluorine atoms being neglected, P₆N₆→P₃N₃+ P₃N₃ and P₇N₇→ P₃N₃+ P₄N₄. The preferred mode of decomposition of the octameric fluoride is into P₄N₄ fragments, though P₃N₃+ P₃N₅ is also important. A comparatively high proportion of P₃N₃ fragments is obtained from (NPF₂)₉. In the larger rings, from (NPF₂)₁₀ upwards, the product specificity tends to be lost, because of the increased variety of possible stable cyclic fragments. More important, for n > 6, the variation in the yields of the smaller cyclic fragments is overshadowed by the increasing and exceptionally high yields, not only of the parent series, but of the parent ion within it, an effect attributed, by analogy with the behaviour of benzene and its homologues, to extensive electronic delocalisation. In addition to the main series of limiting compositions P_nN_nF_2n⁺ and P_nN_{n– 1}F_{2n+ 2}⁺, small amounts of ions of the type P_nN_{n+ 2}F_{2n+ 6}⁺(n= 4–12) have been detected.