C-13 NMR chemical shifts for some alpha -heterosubstituted acetic acids are reported. Me alpha -methylene carbon presents high ICS (Intramolecular Interaction Chemical Shifts') values, which are very similar to those of other series of carbonyl compounds. Neither the ICS or the SCS ("Substituent induced Chemical Shifts") correlate with the usual substituent electronic and/or steric parameters. Those experimental chemical shifts are very close to the ones obtained by theoretical calculations (MP2). Me carbonyl carbon chemical shifts also deviate from the empirically calculated values, but are similar to the theoretically estimated shifts (DFT). These observations indicate that, while the theoretically calculated values match the experimental values, the same does not occur with the ones obtained by empirical methods, which can be valuable tools for checking the occurrence of significant intramolecular interactions between two substituents attached to the same methylene carbon atom.4541795148153