NMR OF TERMINAL OXYGEN .9. O-17 NMR OF THE P-O DOUBLE-BOND - PHOSPHINE OXIDES, PHOSPHINATES, PHOSPHONATES, ACYLPHOSPHONATES AND RELATED-COMPOUNDS

The O-17 NMR spectra of phosphorus-bound oxygen atoms in secondary phosphine oxides (R2HPO, 1), alkyl phosphinates [RHP(O)OR', 2 and R2P(O)OR', 3], dialkyl phosphonates [RP(O)(OR')2, 4], dialkyl acylphosphonates [RCOP(O)(OR')2, 5] and some related compounds were measured. The signals of terminal O appear at high field, only slightly downfield from those of bridge O. Compared with carbonyl O, terminal P-O shows lower sensitivity to structural variations, notably to geminal groups (with the exception of Cl and Br), and a very low sensitivity to arene ring substituents. The difference is discussed in terms of pi-bond character; the carbonyl oxygen of RCOP(O)(OR'), is sensitive to variations in structure.