SummaryThe I7O and 13C chemical shifts (6) of 14 a,p-unsaturated aldehydes and ketones and 33 acyl derivatives RXC= 0 (X= C1, OH, OMe, OEt, NH2 and R = H or alkyl) have been measured. In the unsaturated carbonyl series, a correlation exists between 6 I7O and the n electron density at thep-carbon atom. From this correlation, an6 1 7 0 of 530 ppm was extrapolated for the loss of one electron at the oxygen atom. In the acyl series, the 6 I7O were also sensitive to changes in the polarity of the carbon-oxygen bond. A partial correlation between "0-NMR. chemical shifts and the nuclear quadrupole coupling constants exists for aldehydes, ketones, esters and amides but not for acyl chlorides.Introduction. -The oxygen-17 chemical shifts (6 1 7 0 ) of saturated carbonyl compounds previously studied [ 11 are sensitive to modifications of the electronic density on the oxygen atom through changes in the carbon-oxygen n bond polarity. To verify the validity of this relation in a more diversified series of compounds, we now explore the