NMR chemical shift prediction of carbonyl carbons in amides

The chemical shifts of carbonyl carbons in amides can be estimated using substituent chemical shifts (SCS) for the C and N substituents.
The SCS values used for the calculations are taken from [1].

Literature

[1] "Parameter set for the prediction of the 13C-NMR chemical shifts of sp2- and sp-hybridized carbon atoms in organic compounds"
Pretsch E, Fürst A, Robien W Anal. Chim. Acta 248 (1991) 415-428
picture of amide

R1=
R2=
R3=