17O and 31P NMR of aroylphosphanes, aroylsilanes and aroylphosphonates: Absence of resonance in —COPR2 groups (NMR of terminal oxygen, part 5)

The 17O NMR spectra for aryl‐substituted P,P‐diphenylbenzoylphosphanes (p‐YC6H4COPPh2, 1), trimethylbenzoylsilanes (p‐YC6H4COSiMe3, 2) and dialkyl benzoylphosphonates (p‐YC6H4COPO(OR)2, 3) were recorded. Compounds 1, 2 and 3 show a similar high substituent sensitivity (p+), indicating a strong electron demand of the carbonyl group; as resonance stabilization is not possible in 2 and 3 it is concluded that electron donation from P to carbonyl is equally negligible in 1. The carbonyl oxygen signals of 1, 3 and, in particular, 2 appear at low field. The 31P NMR shifts of 1 were also measured; they are less sensitive to the ring substituents.