“…Dy(dpm) 3 and Tb(dpm) 3 (dpm: 2,2,6,6-tetramethylheptane-3,5-dionate) and Eu(fod) 3 (fod: 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) have been shown to be the most effective shift reagents in 17 O NMR [167][168][169][170]; the mechanism is essentially due to the contact and pseudo-contact shift (see Section 8.5). The shift effect for carbonyl oxygen, extrapolated to [Dy(dpm) 3 ]:[substrate] = 1, is several thousand ppm to low frequency.…”