NMR chemical shift prediction of carbonyl carbons in carboxylic acids and esters

The chemical shifts of carbonyl carbons in carboxylic acids and esters can be estimated using substituent chemical shifts (SCS) for the 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

R1= none Alkyl Chloromethyl Dichloromethyl Trichloromethyl Alkene Phenyl 2-Furyl 3-Furyl 2-Thienyl 3-Thienyl 2-Pyrryl Alkyne Ketone/Aldehyde Carboxylic acid Alkoxy R2= none (acid) Alkyl Alkene Phenyl Anhydride